Diet-Induced Weight Loss: The Effect of Dietary Protein on Bone

RESEARCH Review

Diet-Induced Weight Loss: The Effect of Dietary Protein on Bone Minghua Tang, PhD; Lauren E. O’Connor; Wayne W. Campbell, PhD ARTICLE INFORMATION Article history: Accepted 6 August 2013 Available online 30 October 2013

Keywords: Dietary protein High-protein diet Bone Weight loss Adults

ABSTRACT

High-protein (>30% of energy from protein or >1.2 g/kg/day) and moderately highprotein (22% to 29% of energy from protein or 1.0 to 1.2 g/kg/day) diets are popular for weight loss, but the effect of dietary protein on bone during weight loss is not well understood. Protein may help preserve bone mass during weight loss by stimulating insulin-like growth factor 1, a potent bone anabolism stimulator, and increasing intestinal calcium absorption. Protein-induced acidity is considered to have minimal effect on bone resorption in adults with normal kidney function. Both the quantity and predominant source of protein influence changes in bone with diet-induced weight loss. Higher-protein, high-dairy diets may help attenuate bone loss during weight loss. J Acad Nutr Diet. 2014;114:72-85.

Copyright ª 2014 by the Academy of Nutrition and Dietetics. 2212-2672/$36.00 http://dx.doi.org/10.1016/j.jand.2013.08.021

T

WO THIRDS OF US ADULTS ARE CONSIDERED overweight or obese (body mass index
25) and it is a serious public health concern.1 Weight reduction is recommended for overweight and obese adults to reduce the risks of coronary heart disease and type 2 diabetes. 2 However, body weight is directly associated with bone mass and obese adults usually have higher bone mineral density (BMD) and decreased occurrence of osteoporosis. 3 Weight loss, especially via energy restriction, has been observed in numerous studies to be associated with bone loss.4-6 Therefore, maintenance of BMD after weight loss is extremely important to maintain bone integrity and avoid fracture. Among weight-loss diets, moderately high-protein (1.0 to 1.2 g protein/kg/day or 22% to 29% of total energy consumed) or high-protein (>1.2 g protein/kg/day or >30% of total energy consumed) intake is recommended and promoted because it may help preserve lean body mass7-10 and reduce insulin resistance11 compared with a normal or low-protein intake (at or below the Recommended Dietary Allowance of 0.8 g protein/kg/day). Protein is an important component of bone tissue that by volume contains 50% protein12 and synthesis of bone structure requires a continuous supply of amino acid precursors.13 Multiple studies have evaluated the effects of dietary protein on bone under weight stable conditions. Although dietary protein increases urinary calcium excretion,14-16 it also stimulates intestinal calcium absorption17 and increases the circulating concentration of insulinlike growth factor 1 (IGF-1).18-20 Both intervention21 and observational22 studies have found that a higher dietary protein intake has beneficial effects on bone and inadequate protein intake is associated with increased risk of fractures.23

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A recent meta-analysis also supports a positive association between protein intake and bone health in weight-stable adults.24 However, the potential influence of consuming a higher-protein (ie, moderately high and high) diet as part of a weight loss strategy on bone remains unclear and multiple factors could affect the interpretation of results. Although literature on the influences of dietary protein on bone in weight-stable adults provide important scientific and clinically relevant information, caution is warranted before applying findings from these studies to weight loss conditions because weight loss influences bone metabolism and negatively affects bone. The aim of our review is to analyze and evaluate the effects of dietary protein on bone in conjunction with weight loss by overweight and obese adults and to discuss related dietary and experimental factors. It is recognized that exercise has also been shown to affect bone during weight loss, but this topic is beyond the scope of this particular review article.25 The Figure provides a list of terms, their abbreviations, and their definitions that are used in this review. Protein intake can be expressed as percent of total energy intake or relative to body weight (grams per kilogram body weight per day). Protein intake in percent total energy can be used to compare protein intake with fat and carbohydrate intakes, which are usually presented as percent total energy. Because protein need is closely related to body/lean mass, protein intake is described more often as grams per kilogram body weight per day. In our review, both percent and grams per kilogram body weight per day are presented when information is available. We used a traditional model of literature review as opposed to the more systematic approach recommended

ª 2014 by the Academy of Nutrition and Dietetics.

RESEARCH

High

>30% of energy from protein or >1.2 g/kg/d

Moderately high

22%-29% of energy from protein or 1.0-1.2 g/kg/d

Normal

15%-21% of energy from protein or 0.8-1.0 g/kg/d

Low

<15% of energy from protein or 0.8 g/kg/d, the Recommended Dietary Allowance

Potential renal acid load (PRAL)

PRAL¼[0.49protein (g)]þ[0.037phosphorus (mg)]e [0.021potassium (mg)]e [0.02magnesium (mg)]e [0.013calcium (mg)]a

dietary protein affects bone during weight loss. The Table provides a summary of literature addressing the relation between dietary protein and bone health during weight loss. Listed studies are clinical trials targeting weight loss via energy restriction and reported bone-related parameters (ie, BMD, bone mineral content, bone mass, and bone resorption/formation markers). Protein intake is described as percent total energy intake and relative to body weight (grams per kilogram body weight per day). BMD reductions among the nine studies presented range from 0% to e3.3%. Findings of the effect of dietary protein on bone are not consistent. Some studies32,33,36 found high-protein diets help attenuate BMD loss or bone markers, whereas others found no effect or a detrimental effect of dietary protein on bone during energy-restriction-induced weight loss.29-31,34,35 Different study designs, including the length of intervention, predominant protein sources of the diet, and calcium content, as well as discrepancies in data reporting, can all lead to inconsistency of the results. The following sections will discuss each of these factors and evaluate available evidence in more detail.

Insulin-like growth factor 1 (IGF-1)

An anabolic factor to stimulate calcium accumulation in bone

SULFUR-CONTAINING PROTEIN AND ACID LOAD

Dual-energy x-ray absorptiometry (DXA)

Directly measures bone mineral content (g) and bone area (cm2)

Bone mineral density (BMD)

BMD (g/cm2)¼BMC (g)/bone area (cm2)

Bone mineral content (BMC)

The quantity of bone mineral in the body

Term

Definition

Protein intake

Weight reduction is closely associated with bone loss. Specifically, a 10% weight loss can lead to 0% to 2% BMD loss in adults.27,28 Multiple studies29-36 have assessed the ways

Bone contains 99% of the calcium in the body and serves as a buffer in response to acid stress to release calcium and magnesium.37 A prolonged exposure to an acidic environment could lead to bone resorption and decreased bone mass. Dietary protein is a source of metabolic acid and is reported to decrease urinary pH levels.13 Protein high in methionine and cysteine is believed to be more harmful because these sulfur-containing amino acids are substrates for sulfuric acid synthesis in the body.38 Animal-based protein is reported to be more detrimental than plant-based protein in some studies39,40 because of its higher sulfur content, but not others.22 This could partially be due to the various contents of methionine and cysteine from different protein sources that cannot be simply categorized as animal vs plant protein. Wheat protein, for example, has high sulfur content and could contribute to increased acid load even though it is a plant-based protein source. Some researchers argue that sulfur-containing proteins consumed in the diet cannot lead to metabolic acidosis because the acid yielded is not strong enough for a prolonged effect41 and would not require bone tissue mobilization to release buffer equivalents such as calcium and magnesium.41,42 However, when kidney function, including regulating acid/base homeostasis, is impaired (ie, with aging), a dietary acid load may have a negative effect on calcium balance39,43 because the kidneys are no longer capable of filtering acid efficiently. Thus, a healthy adult consuming protein from the diet should not be at risk for bone loss due to increased acidity. Evidence from weight-stable subjects is also inconclusive. A 7-year follow-up of postmenopausal women39 showed that a higher ratio of animal/vegetable protein intake was associated with a greater risk of hip fracture, but not low BMD. In the Nurses’ Health Study,40 higher animal protein consumption was associated with an increased risk of forearm fracture, but not hip fracture. Moreover, women who consumed five or more servings of beef, pork, or lamb per week had an increased forearm fracture risk than women who consumed less than one serving of red meat per week.40 On the other

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a

Remer T, Manz F. Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc. 1995;95(7):791-797. Figure. Terms used in a review designed to analyze and evaluate the effects of dietary protein on bone in conjunction with weight loss by overweight and obese adults and to discuss related dietary and experimental factors. by the Academy of Nutrition and Dietetics.26 This approach was taken because we describe multiple important topics regarding dietary protein, weight loss, and bone, rather than one or two feasibly done for a systematic review. Also, we did not conduct a specific systemic review because the mechanistic data and scientific perspectives imbedded in many publications are not readily or comprehensively obtained and gleaned from the publications based on key words or medical subject heading terms. As such, this article should not be considered a comprehensive review of the topic-specific literature. A PubMed search using key words protein, weight loss, and bone was used to filter literature, followed by a customized search of research article bibliographies.

DIETARY PROTEIN’S EFFECT ON BONE DURING WEIGHT LOSS

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RESEARCH hand, the Framingham Osteoporosis Study22 found that lower animal protein intake was associated with BMD loss of the femur and spine. Soy protein has shown no differences in BMD compared with control protein sources in short- and long-term studies.44,45 To quantify the acid stress potential of proteins from difference sources, the potential renal acid load (PRAL) based on the amino acid compositions of various animal and vegetable protein sources was calculated.46 The results showed that oatmeal, whole wheat, and white rice all have higher PRAL than pork, beef, and milk, indicating grouping protein as animal or vegetable origins does not correctly represent a PRAL difference.41 In addition, because protein is most likely to be consumed in a meal rather than purified protein alone, the potential acid load of other food items consumed together with protein also needs to be considered. In fact, when protein with high PRAL is accompanied by fruits and vegetables, which are low in protein but high in potassium (a base mineral), the overall acid load of the diet is minimized.47 Under conditions of weight loss, data of acid load induced by dietary protein on bone are very limited (Table). Only Campbell and Tang29 reported PRAL of the diets with regard to bone health. Both studies showed that postmenopausal women lost more BMD when consuming a moderately high (26% protein, 1.0 g protein/kg/day, Campbell and Tang Study 829) or high-protein (30% protein, 1.4 g protein/kg/day, Campbell and Tang Study 729) diet mainly from animal sources. PRAL was calculated based on the diet, not just dietary protein, and this approach should give a more accurate assessment of diet-induced acidity, as discussed before. Although BMD losses were comparable between Campbell and Tang’s Study 7 and 8,29 the PRAL of the higher-protein diet was fivefold higher in one study than in the other. The authors speculated that in human beings with normal kidney function, PRAL was not a significant factor with regard to BMD changes during weight loss. Based on the limited evidence available, it appears that acidity induced by dietary protein is negligible in terms of bone health during weight loss.

PROTEIN AND CALCIUM BALANCE Approximately half of the volume of bone structure is protein and the other half is calcium and phosphorus crystal.48 Calcium is lost daily from the body and if calcium intake from the diet does not offset the loss, a calcium imbalance will occur and calcium will be released from bone, the calcium reservoir.49 Thus, it is evident that chronic low calcium consumption would eventually lead to bone loss. Numerous intervention50-52 and observational53,54 studies have demonstrated a beneficial effect of calcium consumption on bone mass accretion. For example, fracture risks can be significantly reduced by 60% with a lifetime of high (1,300 to 1,700 mg/day) calcium intake.55 It is well documented that dietary protein increases urinary calcium excretion14-16 despite varied experimental designs, protein sources and lengths of study with weight-stable subjects.56 An increase of protein intake from 75 to 125 g/ day can lead to a 64 mg/day increase in calcium excretion, which could result in up to 2% annual bone loss.57 Indeed, a long-standing belief existed that a higher-protein (>22% energy from protein) diet was detrimental to bone due to a 74

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greater calcium excretion.16 However, with the use of calcium isotopes and the ability to evaluate intestinal calcium absorption, this notion was revisited56 and the observation was made that the main source of the excreted calcium seems to be from the intestine because dietary protein increases intestinal calcium absorption.20,58-60 Thus, increased protein consumption increases calcium turnover rather than absolute calcium loss if enough dietary calcium is consumed. Two more recent studies have looked at the effect of increasing dietary protein intake approximately from 0.85 to 1.70 g/kg/day for 7 weeks on intestinal calcium absorption and urinary calcium excretion in postmenopausal women.61,62 Consistent results were found in these two studies that a higher calciuria was accompanied by higher calcium absorption. There was no net loss of calcium61,62 and the influence of protein on calciuria was independent of calcium intake.61 In addition, the concentration of serum IGF1 (a potent bone anabolism stimulator63) significantly increased with a higher protein intake in both studies. Researchers have assessed urinary calcium excretion with higher-protein diets during weight loss30,32,34,35 (Table) and results are mixed. Bowen and colleagues30 found that urinary calcium excretion decreased (e1.090.3 mmol/day) over time independent of dietary protein intake. This finding is consistent with Noakes and colleagues35 in which urinary calcium excretion decreased by 0.8 mmol/day. Li and colleagues34 found no effect of time or diet on urinary calcium excretion among subjects. Thorpe and colleagues35 reported a decrease of urinary calcium excretion in the normal-protein group only, not in the high-protein group, although changes were not quantified. The median daily urinary calcium excretion was 167 mg for high-protein group subjects and 98 mg for normal-protein group subjects during the intervention. Because the high-protein group consumed 300 to 400 mg/day more calcium than the normal-protein group, the authors speculated that the additional calcium absorbed would compensate for the urinary calcium loss in the highprotein group.32 Calcium absorption was not measured in any of the above studies. Although data are limited and study designs varied, it appears that compared with a normal protein diet, a high-protein diet either has no effect or a negative effect on calcium homeostasis by not preserving or increasing calcium excretion. The influence of protein on calcium balance during weight loss still needs to be investigated with measurement of both calcium absorption and excretion.

PROTEIN AND IGF-1 IGF-1, one of the most copious growth factors in human bone, plays an important role in maintaining bone homeostasis, including increasing osteoblast activity64 and stimulating renal phosphate reabsorption.65 Refer to Giustina and colleagues66 for more mechanistic details of IGF-1. In studies in human beings, a persuasive body of evidence exists on the positive effect of IGF-1 on bone health such as attenuating proximal femur BMD loss in elderly men and women with recent hip fracture,18 decreasing urinary bone resorption markers deoxypyridinoline67 and N-telopeptide,19,20 and being positively associated with BMD at five different skeletal sites.68 A potential mechanism by which protein exerts a beneficial effect on bone is via IGF-1.69 Free amino acids, January 2014 Volume 114 Number 1

RESEARCH especially arginine, are shown in vitro to increase IGF-1 production.70 It was found that higher protein consumption is associated with a higher serum IGF-1 concentration.18,19 Protein source as well as protein quantity may influence serum IGF-1 regulation because serum IGF-1 concentration was higher in subjects who consumed protein from milk sources.19,71 A comparison of total, meat, and dairy protein consumption in healthy, prepubertal boys showed that IGF-1 concentration was positively associated with dairy, but not meat protein,72 although results from another observational study showed that consumption of red meat, fish, and seafood were all modestly correlated with IGF-1 in middle-aged and elderly men.73 A difference in subjects’ age from these two studies may contribute to the difference of the results because there is a higher calcium turnover and positive calcium balance during growth. In addition, compared with dairy protein, soy protein was found to have a more pronounced effect on serum IGF-1 in postmenopausal women.67 The effect of IGF-1 on bone is well documented, but the association between dietary protein and IGF-1 during weight loss is not as clear. Only two of nine studies presented measured IGF-1 (Table). Sukumar and colleagues33 reported an increase in serum IGF-1 concentration (20%37%) in the higher-protein group compared with no change (3%18%) in the normal-protein group, and an attenuated BMD loss at the ultradistal radius (e0.9%3.2% vs e3.34.2%), lumbar spine (0.2%3.4% vs e1.4%3.6%), and total hip (e0.4%1.3% vs 0.2%3.4%) compared with the normal-protein group. Weight losses were not different between groups. In Campbell and Tang’s Study 8,29 weight losses were not different among the three weight-loss groups, but only subjects consuming higher protein significantly decreased total body BMD from baseline (CHICKEN: e1.1%0.3%, BEEF: e1.4% 0.2%). Serum IGF-1 concentration did not change over time in any groups. The study done by Sukumar and colleagues33 was 12 months and Campbell and Tang’s Study 829 was 9 weeks. There is a possibility that the length of Campbell and Tang’s Study 829 was too short to observe an increase in IGF-1 concentration that can contribute to BMD preservation as seen by Sukumar and colleagues,33 but evidence is too limited to draw conclusions. In addition, IGF-1 secretion can be affected by energy status. A negative energy balance (ie, during weight loss) can reduce the sensitivity of growth hormone receptor and decrease circulating IGF-1 concentration,74 which may partially explain the results in Campbell and Tang’s Study 8.29 Overall, it appears that IGF-1 has a positive effect on bone during weight loss, but findings of the effect of dietary protein on IGF-1 during weight loss are inconclusive.

Dairy products are excellent sources of calcium, compared with most other typically consumed food items.12 The vast majority of both controlled trials and observational studies with weight-stable conditions showed a positive association between dairy foods and bone health and there were no negative reports, according to The 2010 Dietary Guidelines for Americans.75 In postmenopausal women, milk products suppress bone resorption to a greater extent than calcium carbonate.76 A 2-year randomized control trial found school girls

(aged 10 to 12 years) who consumed 1,000 mg/day calcium from cheese had a greater positive change in tibia thickness compared with the groups consuming calcium phosphate and vitamin D supplements.77 However, the effect of dietary protein was not addressed in these studies. The difference in protein intakes between groups due to different dairy consumption might be a confounding factor of the observed differential responses in bone. As suggested by Cheng and colleagues77 there might be additional possible mechanisms with dairy products. For example, caseinphosphopeptide or lactose in dairy foods can facilitate intestinal calcium absorption78 and compared with calcium supplement, calcium consumption via dairy foods is more evenly distributed and could result in greater absorption.77 In addition, milk’s basic protein contains stimulating factors such as high mobility group-like protein, kininogen fragment 1.2, and cystatin C, could increase bone formation and decrease bone resorption.79,80 Collectively, dairy products appear to stimulate bone anabolism with a weight-stable state.12 The effect of dairy products on bone during weight loss has also been studied (Table). In the study by Skov and colleagues31 the high-protein diet contained protein mainly from dairy and meat, although sources were not quantified. After 6 months of weight loss, bone mineral content was lost in all subjects independent of protein intake (low protein e6213 g, high protein e11113 g). The high-protein group lost more weight (8.9 vs 5.1 kg) and fat (7.6 vs 4.3 kg) and consumed more calcium (317 mg difference) compared with the low-protein group. The authors further adjusted bone mineral content for fat loss between groups and found that high dietary-protein intake was associated with less bone mineral content loss, although it cannot be assumed that bone mineral content is lost proportionally with fat mass loss. In addition, adjusting for body composition changes may not be practical because the differences of body composition changes between groups could be caused by different protein intakes. Thorpe and colleagues32 found that consuming a high-protein, high-dairy diet (1.4 g/kg/day) with three servings of dairy per day was associated with higher BMD at total body, lumbar spine, and total hip compared with a normalprotein diet (0.8 g/kg/day) with two servings of dairy per day over 12 months. Measurements were taken at baseline and Intervention Month 4, 8, and 12. However, BMD data at baseline were not reported and the effect of time on BMD was also not reported so the changes of BMD over time at different bone sites are not known. No difference in weight loss (8.9% to 12% loss in all subjects) was found between groups and the calcium content of the high-protein, highdairy diet was higher than the control group (Table). The authors stated, “our data do not permit the resolution of independent or interactive effects of protein and other dairy components such as calcium and vitamin D but support the effectiveness of a high-protein, high-dairy diet for protecting bone health during weight loss in free-living patients.”32 In the study done by Bowen and colleagues,30 obese adults consuming a higher-protein (1.2 g/kg/day), weight-loss diet for 16 weeks had a lower bone turnover rate when protein was predominantly from dairy vs meat and no changes in BMD was observed. The authors suggested a modest advantage of the high-dairy protein diet by minimizing overall bone turnover. One limitation of the study was the huge difference in calcium intake (2,400 mg/day in the dairy group

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Study Reference 1

2

Subjects

Overweight men Thorpe and and women colleagues32

Design

Body composition results

12-mo weight loss trial with counseling to reduce energy intake

Bone results Calcium intake: normal-protein group 670-1,150 mg/d; high-protein group 820-1,380 mg/d. High-protein group consumed more calcium than normal-protein group

n¼66 Men 39-53 y; Women 41-52 y

Normal-protein group: w0.8 g protein/kg/d; 15% protein, 55% carbohydrate, 30% fat; 2 servings of dairy daily

n/ab

Total body BMDc, lumbar spine, and total hip BMD levels in normal-protein group were lower than in high-protein group over the course of the intervention

n¼64 Men 39-55 y; Women 35-51 y

High-protein group: w1.4 g protein/kg/d; 30% protein, 40% carbohydrate, 30% fat; 3 servings of dairy daily

n/a

Urinary calcium excretion decreased by Month 8 in the normal-protein group, and was maintained in the high-protein group

Sukumar and Overweight and obese 12-mo weight loss trial using colleagues33 energy-restricted (w500-600 kcal postmenopausal [2,092-2,510 kJ] energy deficit) women diet plan and counseling

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n¼21 575 y

Normal-protein group: w18% protein (w0.8 g protein/kg/d)

n¼26 594 y

High-protein group: w30% protein (w1.0 g protein/kg/d); whey protein supplements were provided

Calcium intake was maintained at 1,200 mg/d for all subjects. Normal protein group lost more BMD at the ultradistal radius, lumbar spine, and total hip than high-protein group. Total body, hip, and radius BMCd were lost over time independent of diet Subjects lost 11.7%10.1% fat mass and 2.7%4.0% lean mass with no difference between groups

BMD lost at ultradistal radius (e3.3%4.2%), lumbar spine (e1.4%3.6%), and total hip (e1.2%1.8%); Bone resorption marker (deoxypyridinoline) increased in the normal-protein group only BMD lost at ultradistal radius (e0.9%3.2%), lumbar spine (0.2%3.4%), and total hip (e0.4%1.3%); high-protein group had a greater intake of dairy and meat than the normal-protein group; IGF-1e level increased (20%37%) in the high-protein group only (continued on next page)

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Table. Published studies of dietary protein and bone during weight lossa

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Table. Published studies of dietary protein and bone during weight lossa (continued) Study Reference 3

4

Subjects

Design

Body composition results

Bone results 24-h urinary calcium excretion decreased in all subjects (e1.090.23 mmol/d)

Bowen and Overweight and obese 12-wk controlled feeding of energy colleagues30 men and women restricted 1,315 kcal/d (5,500 kJ/d), high-protein diet: 35% protein, 41% carbohydrate, 24% fat n¼25 Men: 493 y; Women: 472 y

High dairy-protein group: 1.2 g protein/kg/d; 62% dairy; calcium content was 2,400 mg/d

n/a

No change in BMD; smaller increase of deoxypridinoline than mixed-protein group; osteocalcin did not change

n¼25 Men: 494 y; Women: 463 y

High mixed-protein group: 1.2 g protein/kg/d; 5% dairy; calcium content was 500 mg/d

n/a

No change in BMD; deoxypyridinoline and osteocalcin both increased

Skov and Overweight men colleagues31 and women

n¼15 382 y

Control: habitual diet

No fat loss

n¼25 402 y

Low-protein group: 0.8 g protein/kg/d; 12% protein, 58% carbohydrate, 30% fat

Decrease of total body BMC (e8513 g) Low-protein group had 4.3 kg significantly different from fat loss; significantly different control group from high-protein group. Low-protein group lost 0.9 kg lean mass; no different from high-protein group

n¼25 402 y

High-protein group: 1.25 g protein/kg/d; 25% protein, 45% carbohydrate, 30% fat

High-protein group had 7.6 kg fat loss; significantly different from low-protein group. High-protein group lost 1.3 kg lean mass; no different from low-protein group

Decrease of total body BMC (e11113 g) significantly different from control group

(continued on next page)

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Calcium intake: control 991138 mg/d, low protein 65940 mg/d, high protein 93679 mg/d Total body BMD remained constant over time in all subjects Total body BMC didn’t change

6-mo, dietary weight-loss intervention controlled for macronutrient composition; protein sources for low-protein and high-protein groups are primarily dairy and meat

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Table. Published studies of dietary protein and bone during weight lossa (continued) Study Reference 5

6

Subjects

Design

Body composition results

Bone results

There was no effect of time or diet on total body BMD or urinary calcium excretion

Overweight and obese 12-mo controlled feeding using Li and men and women 500 kcal (2,092 kJ) energy colleagues34 deficit meal plans n¼41 509 y

Normal-protein group: 15% protein (1.1 g protein/kg lean body mass/d), 55% carbohydrate, 30% fat; carbohydrate powder added to the diet

Normal-protein group did not lose a significant amount of fat. Significantly decreased lean body mass; no differences between groups

n¼44 4912 y

High-protein group: 30% protein (2.2 g protein/kg lean body mass/d), 40% carbohydrate, 30% fat; protein powder added to the diet

High-protein group lost a significant amount of fat; high-protein group lost significantly more fat mass than normal-protein group. Significantly decreased lean body mass; no differences between groups

Noakes and Overweight and colleagues35 obese women

12-wk controlled feeding 1,338 kcal/d (5,600 kJ/d)

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n¼48 499 y

Normal-protein group: 17% protein (w0.7 g protein/kg/d), 64% carbohydrate, 20% fat

n¼52 5010 y

High-protein group: 34% protein (w1.3 g protein/kg/d), 46% carbohydrate, 20% fat. High protein was achieved by consuming dairy and lean meat

Diet had no overall effect on fat loss in either group

Bone turnover markers increased by 8%-12% and calcium excretion decreased by 0.8 mmol/d in all subjects

(continued on next page)

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Table. Published studies of dietary protein and bone during weight lossa (continued) Study Reference

Subjects

7

Overweight and obese 12-wk, 750 kcal (3,138 kJ) energy deficit diet controlled feeding; postmenopausal 800 mg/d calcium and women multivitamin supplements

Campbell and Tang29

Body composition results

Bone results PRALf of the diets: normal protein 6.4-13.7 mEq/d; high protein 29.1-42.2 mEq/d. Calcium intakes: normal protein 2,03046 mg/d; high protein 2,21055 mg/d

n¼15 603 y

Normal-protein group: 0.8 g protein/kg/d, 18% protein, 57% carbohydrate, 25% fat; lacto-ovo-vegetarian diet; 53% of protein came from dairy

Showed a significant loss over time in fat and lean mass but no difference between diet groups

Total body BMD did not change in normal protein group: e0.3%0.2%, e0.0030.003 mg/cm2, BMC or bone area did not change

n¼13 512 y

High-protein group: 1.4 g protein/kg/d, 30% protein, 45% carbohydrate, 25% fat; omnivorous diet; 36% of protein came from dairy

Showed a significant loss over time in fat and lean mass but no difference between diet groups

Total body BMD decreased in high-protein group: e1.4%0.4%, e0.0170.004 mg/cm2. BMC or bone area did not change

Overweight and obese 9-wk, controlled feeding; 1,000 kcal postmenopausal (4,184 kJ) lacto-ovo-vegetarian women basal diet plus 250 kcal/d (1,046 kJ/d) shortbread cookies or chicken breast or beef tenderloin. The control group consumed habitual diet

PRAL of the diets: shortbread cookies e5.5 mEq/d, chicken breast 6.9 mEq/d, beef tenderloin 5.4 mEq/d. Calcium intakes: control 928126 mg/d, shortbread cookies 89792 mg/d, chicken breast 78380 mg/d, beef tenderloin 63065 mg/d Hormones: IGF-1 concentration did not change

n¼11 545 y

Control: habitual diet

Total body BMD, BMC, or bone area did not change overtime

n¼14 592 y

Normal-protein group: 16% protein (0.7 g protein/kg/d), 58% carbohydrate, 26% fat; 20% of protein came from dairy

Lost 3.90.4 kg fat mass; significantly different from control Lost 1.70.3 kg lean mass; significantly different from control

Total body BMD, BMC, or bone area did not change overtime

(continued on next page)

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8

Campbell and Tang29

Design

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Table. Published studies of dietary protein and bone during weight lossa (continued) Study Reference

9

Subjects

Design

Body composition results

Bone results

n¼15 602 y

Moderately high-protein (chicken) group: 26% protein (1.0 g protein/kg/d), 48% carbohydrate, 26% fat; 20% of protein came from dairy

Total body BMD decreased in moderatelyehigh-protein (chicken) group: e1.1% 0.3%, e0.01230.003 mg/cm2. BMC or bone area did not change

n¼14 582 y

Moderatelyehigh-protein group (beef): 26% protein (1.0 g protein/kg/d), 48% carbohydrate, 26% fat; 20% of protein came from dairy

Lost 5.60.6 kg fat mass; significantly different from control Lost 2.30.3 kg lean mass; significantly different from control Lost 4.30.6 kg fat mass; significantly different from control Lost 2.20.3 kg lean mass; significantly different from control

Total body BMD decreased in moderatelyehigh-protein (beef) group: e1.4%0.2%, e0.01450.003 mg/cm2. BMC or bone area did not change

Calcium intake: normal protein, low dairy group 29922 mg/d; normal protein, moderate dairy group 1,20019 mg/d; high protein, high dairy group 1,84013 mg/d. No significant changes in BMD was observed in any group

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Josse and Overweight and colleagues36 obese women

16-wk weight loss trial using energy-restricted diet plan (500 kcal (2,092 kJ) energy deficit) and counseling/exercise protocol

n¼30 Women 281 y

Normal protein, low dairy group: 0.720.02 g protein/kg/d; 16% protein, 56% carbohydrate, 28% fat; 0-1 servings dairy daily

Significant fat loss over time Lean mass decreased (0.70.3 kg)

C-telopeptide, urinary deoxypyridinoline, and osteocalcin increased; P1NPg to CTXh ratio decreased

n¼30 Women 261 y

Normal protein, moderate dairy group: 0.84 g protein/kg/d; 18% protein, 58% carbohydrate, 24% fat; 3-4 servings dairy daily

Significant fat loss over time Lean mass unchanged (0.20.2 kg)

P1NP increased

(continued on next page)

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a The majority of the studies listed in the Table showed little to no differences between low protein (LP) and high protein (HP) groups for changes in fat mass, lean mass, and bone mass. Two studies (Skov and colleagues31 and Li and colleagues34) showed increases in fat mass in the HP groups, whereas the others showed no difference between groups. Campbell and Tang29 showed a larger decrease in bone mineral density (BMD) in HP group than compared with the LP group but Sukumar and colleagues33 showed the opposite. As far as lean mass is concerned, it was shown by Josse and colleagues36 that with increasing dairy consumption, lean body mass was preserved and increased; the other studies found no differences between groups. b n/a¼not available. c BMD¼bone mineral density. d BMC¼bone mineral content. e IGF-1¼insulin-like growth factor 1. f PRAL¼potential renal acid load. g P1NP¼procollagen type 1 N propeptide. h CTX¼C-terminal telopeptide of type 1 collagen.

High protein, high dairy group: 1.33 g Significant fat loss over time; Osteocalcin and P1NP increased; P1NP to CTX and osteoprotegerin to receptor significantly greater loss protein/kg/d; 28% protein, 41% activator of nuclear factor-kB ligand in latter half of study carbohydrate, 31% fat; 6-7 compared with other servings dairy daily ratios increased diet groups Lean mass increased (þ0.70.3 kg) n¼30 Women 301 y

Study Reference

Table. Published studies of dietary protein and bone during weight lossa (continued)

Body composition results

Bone results Design Subjects

RESEARCH and 500 mg/day in the meat group),30 which could confound the results. In addition, a high bone turnover rate does not necessarily mean a potential bone loss would occur if calcium intake is adequate. A recent 16-week study (Josse and colleagues36) assessed the effects of consuming different quantities of dairy during weight loss on markers of bone turnover in overweight and obese women. Results showed that consuming a high-protein diet (w1,800 mg calcium/day) with 7 to 8 servings of dairy per day had a more positive effect on bone turnover markers than consuming a normalprotein diet (w300 mg calcium/day) with 0 to 1 servings of dairy per day, although there was no change in BMD or bone mineral content among the subjects. All subjects underwent resistance and aerobic exercise throughout the intervention. Collectively, findings from these studies indicate that a higher-protein diet with dairy as the major protein source may be beneficial to bone health during weight loss,30-32 but this beneficial effect could be confounded by an inherent high calcium and vitamin D intake with dairy. With the amount of calcium intake controlled and kept high (>2,000 mg/day) for all subjects, Campbell and Tang’s Study 729 assessed the effects of a high-protein (1.2 g/kg/day) weight-loss diet on bone in postmenopausal women for 12 weeks with protein mainly from pork (40%) and dairy (36%) compared with the normal-protein (0.8 g/kg/day lactovegetarian, 53% dairy) group.29 Total body BMD was lost with the high-protein, high-calcium diet only (Table). In contrast, Sukumar and colleagues33 showed that the higherprotein diet with a greater content of meat and dairy attenuated loss of BMD at the ultradistal radius, lumbar spine, and total hip, with all subjects consuming 1,200 mg/day calcium. Studies indicated a greater relative intake of dairy protein in the higher-protein vs the lower-protein group all found a beneficial effect of higher-protein diet on bone,30,32,33 regardless of calcium intake,33 but dairy content was not quantified. Only Campbell and Tang’s Study 729 quantified dairy protein consumptions of the subjects as 42 and 36 g/ day in the higher- and normal-protein diets (based on a 1,550 kcal/day diet), respectively, and outcomes of total body BMD did not favor the higher-protein diet, even though calcium consumption was more than 2,000 mg/day in all subjects. Note that the higher-protein group in Campbell and Tang’s Study 729 also contained comparable quantities of meat protein (46 g/day based on a 1,550 kcal/day diet). Overall, it appears that besides protein quantity, protein source may be an important factor affecting bone during weight loss, although studies systematically comparing protein sources and quantity are needed. Most studies are not able to compare protein sources alone due to the design of the diets (different in both source and quantity between groups). Campbell and Tang’s Study 829 is the only study that allows comparison between two protein sources: chicken and beef (Table). The diets in Campbell and Tang’s Study 829 contained a vegetarian basal diet (1,000 kcal/ day) for all subjects and 250 additional calories of energy from shortbread cookies, chicken breast, or beef tenderloin. Thus, difference between the chicken breast and the beef tenderloin groups reflects the potential difference in these two protein sources. Results showed that total body BMD loss was not different between the two groups but were greater than the shortbread cookies group. Findings from Campbell and Tang’s studies29 indicated that consuming a JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS

81

RESEARCH higher-protein diet with protein predominantly from animal flesh sources promoted BMD loss, although more research is needed to verify these findings. To our knowledge, there is no direct comparison available to test any potential effects between animal flesh sources and plant-based sources of protein; thus, no conclusion can be drawn from this perspective. Among healthy prepubertal boys, high protein intakes from dairy vs meat differentially influenced serum markers of bone turnover, and serum IGF-1 was positively associated with dairy, but not meat protein.72 The authors suggested that dairy and meat proteins may have distinct regulatory effects on bone during growth. Although growth and weight loss have contrasting effects on bone (net retention vs net resorption), they both are periods of increased bone turnover and changes in bone mass that might be differentially influenced by the source of protein consumed to achieve quantitatively higher protein intakes. Collectively, it appears that calcium itself cannot preserve the loss of bone accompanied with weight loss,29 and dairy protein with additional nutrients in dairy products, compared with other protein sources, may have a positive influence on bone health.12,30,32,33 The optimal quantity of dairy one should consume during weight loss to attenuate bone loss remains to be established.29 Future studies are suggested to focus on differentiating the effects of protein quantity and sources on bone during weight loss, including dairy, meat, and plant sources and avoid confounding factors such as calcium intake. Measurements of IGF-1, calcium absorption, and bone resorption could greatly help us understand the dynamics of bone turnover during weight loss.

BONE REMODELING AND LENGTH OF INTERVENTION Bone, like other tissues in the body, is continuously turning over or remodeling81 to maintain integrity, replace old or damaged bone, and adapt to mechanical load changes.12 In adults, bone remodeling replaces 8% to 10% of bone per year.82 Interventions with bone parameters as outcomes need to be interpreted with caution due to the effect of bone remodeling. A long-term effect of calcium supplementation on bone loss in perimenopausal women is an example of how dietary interventions alter bone remodeling.82,83 In this study, perimenopausal women consumed supplements with 0 (control group), 1,000 mg, or 2,000 mg calcium daily for 3 years.83 BMD was measured at baseline and the end of Years 1, 2, and 3. There was no BMD loss in the 2,000 mg calcium group at Year 1, but this suppression diminished overtime and at the end of Year 3 all three groups of women had nearly the same degree of BMD loss.82,83 Clearly, calcium supplementation only delayed the occurrence of bone loss; but if the intervention only lasted for 1 year or less, a different conclusion could be drawn to favor a preservation effect of 2,000 mg calcium supplements on BMD. A bone remodeling transient is a temporary phase lag between the normally coupled bone formation and resorption process usually caused by nutritional interventions.84 Heaney suggested that “steady-state effects of any given nutrient intake can only be ascertained by measurements made after the transient has passed.”82 The bone remodeling transient can last several months82 or more than a year83 depending on the nature of the intervention. Notice that no available 82

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research was conducted for longer than 12 months during which time the bone remodeling transient may still be in process. The inconsistent results from different studies11,29-33 may be partially due to different lengths of the interventions (9 weeks to 12 months). The shorter interventions showed little to no change in bone homeostasis,11,26 unless the main protein source was dairy which then showed a moderate superiority in minimizing bone turnover.28 The longer studies ranging from 6 to 12 months showed that a higher protein diet was associated with less bone loss.29,30,31

OTHER CONSIDERATIONS Dual-energy x-ray absorptiometry (DXA) is a standard and the most widely used technique to determine BMD since the late 1980s.85 DXA directly measures bone mineral content (grams) and bone area (centimeters2). BMD (grams/centimeters2) is then calculated as bone mineral content (grams)/ bone area (centimeters2). The measurement of bone area can be affected by tissue thickness and body composition changes. Fat mass loss during weight loss can affect tissue thickness and bone area measurement and lead to an apparent change of BMD derived from bone mineral content and bone area.86 One study enrolled obese women in a 15week weight loss program and DXA was used to measure body composition and bone parameters.87 No significant difference was found with bone mineral content, but a trend of a larger measured bone area led to a decrease in BMD. The authors concluded that the observed BMD may have been the result of a lack of instrument sensitivity and an artifact rather than physiologic change and recommended future research to not only report BMD, but also bone mineral content and bone area.87 Apparently, only one study (Campbell and Tang’s Study 729) on dietary protein and bone in conjunction with weight loss reported all three parameters. Noakes and colleagues35 and Josse and colleagues36 used DXA to measure body composition but only bone turnover markers were reported in terms of bone health. Although bone turnover markers are important parameters to monitor bone health, they are not direct measurements of bone and have a greater variation compared with a DXA scan. When reporting results, it would be helpful to include DXA-measured bone parameters if they are available. BMD obtained from DXA is a two-dimensional measurement and does not take into account bone thickness. Because bone thickness is usually greater with higher body weight, reporting results in BMD can lead to an underestimation of density in overweight and obese individuals.4 New techniques, such as quantitative computed tomography directly assess bone density in 3 dimensions (grams per centimeters3) and should be considered a more reliable approach for bone density measurements.88 One recent study89 using high-resolution magnetic resonance imaging found the microarchitecture of trabecular bone was not affected by energy-restriction even though BMD measured by DXA was found to be lower.

CONCLUSIONS Collectively, protein-induced acidity seems to have a minor influence on calcium balance during weight loss that usually doesn’t affect bone in people with normal kidney function. Protein source and protein quantity are both important factors that could influence bone health during weight loss. January 2014 Volume 114 Number 1

RESEARCH Dairy-source protein has been studied more thoroughly than other protein sources. Current evidence suggests a highprotein, high-dairy diet is associated with attenuating BMD loss during weight loss, possibly due to the stimulation of IGF-1. Direct comparisons of dietary protein sources at specified quantities and measurements of IGF-1, calcium absorption, and bone resorption could greatly improve understanding of the dynamics of bone turnover and maintenance during weight loss. These types of systematic evaluation are needed to help consumers and health care professionals make sound dietary protein choices and recommendations, especially to individuals at high risk of osteoporosis and fractures.

References

recent hip fracture. A randomized, double-blind, placebo-controlled trial. Ann Intern Med. 1998;128(10):801-809. 19.

Heaney RP, McCarron DA, Dawson-Hughes B, et al. Dietary changes favorably affect bone remodeling in older adults. J Am Diet Assoc. 1999;99(10):1228-1233.

20.

Dawson-Hughes B, Harris SS, Rasmussen H, Song L, Dallal GE. Effect of dietary protein supplements on calcium excretion in healthy older men and women. J Clin Endocrinol Metab. 2004;89(3):1169-1173.

21.

Geinoz G, Rapin CH, Rizzoli R, et al. Relationship between bone mineral density and dietary intakes in the elderly. Osteoporos Int. 1993;3(5):242-248.

22.

Hannan MT, Tucker KL, Dawson-Hughes B, Cupples LA, Felson DT, Kiel DP. Effect of dietary protein on bone loss in elderly men and women: The Framingham Osteoporosis Study. J Bone Miner Res. 2000;15(12):2504-2512.

23.

Delmi M, Rapin CH, Bengoa JM, Delmas PD, Vasey H, Bonjour JP. Dietary supplementation in elderly patients with fractured neck of the femur. Lancet. 1990;335(8696):1013-1016.

24.

Darling AL, Millward DJ, Torgerson DJ, Hewitt CE, Lanham-New SA. Dietary protein and bone health: A systematic review and metaanalysis. Am J Clin Nutr. 2009;90(6):1674-1692.

25.

Guadalupe-Grau A, Fuentes T, Guerra B, Calbet JA. Exercise and bone mass in adults. Sports Med. 2009;39(6):439-468.

26.

Methodology: What is the Academy of Nutrition and Dietetics (formerly American Dietetic Association) Evidence Analysis Process? http://andevidencelibrary.com/category.cfm?cid¼7&cat¼ 0&CFID¼15457634&CFTOKEN¼c98e770554b4023b-0CCF5547-22191F3D-44FECC71A3FFE975&jsessionid¼58309f801e4869431070113 d142a53e5a653. Accessed September 16, 2013.

27.

Ricci TA, Chowdhury HA, Heymsfield SB, Stahl T, Pierson RN Jr, Shapses SA. Calcium supplementation suppresses bone turnover during weight reduction in postmenopausal women. J Bone Miner Res. 1998;13(6):1045-1050.

1.

Flegal KM, Carroll MD, Ogden CL, Curtin LR. Prevalence and trends in obesity among US adults, 1999-2008. JAMA. 2010;303(3):235-241.

2.

Church T. Exercise in obesity, metabolic syndrome, and diabetes. Prog Cardiovasc Dis. 2011;53(6):412-418.

3.

Villareal DT, Apovian CM, Kushner RF, Klein S. Obesity in older adults: Technical review and position statement of the American Society for Nutrition and NAASO, The Obesity Society. Obes Res. 2005;13(11):1849-1863.

4.

Reid IR. Relationships among body mass, its components, and bone. Bone. 2002;31(5):547-555.

5.

Jensen LB, Quaade F, Sorensen OH. Bone loss accompanying voluntary weight loss in obese humans. J Bone Miner Res. 1994;9(4): 459-463.

6.

Pritchard JE, Nowson CA, Wark JD. Bone loss accompanying dietinduced or exercise-induced weight loss: A randomised controlled study. Int J Obes Relat Metab Disord. 1996;20(6):513-520.

28.

Johnston CS, Tjonn SL, Swan PD. High-protein, low-fat diets are effective for weight loss and favorably alter biomarkers in healthy adults. J Nutr. 2004;134(3):586-591.

Reid IR, Ames RW, Evans MC, Gamble GD, Sharpe SJ. Effect of calcium supplementation on bone loss in postmenopausal women. N Engl J Med. 1993;328(7):460-464.

29.

Westerterp-Plantenga MS, Rolland V, Wilson SA, Westerterp KR. Satiety related to 24 h diet-induced thermogenesis during high protein/carbohydrate vs high fat diets measured in a respiration chamber. Eur J Clin Nutr. 1999;53(6):495-502.

Campbell WW, Tang M. Protein intake, weight loss, and bone mineral density in postmenopausal women. J Gerontol A Biol Sci Med Sci. 2010;65(10):1115-1122.

30.

Bowen J, Noakes M, Clifton PM. A high dairy protein, high-calcium diet minimizes bone turnover in overweight adults during weight loss. J Nutr. 2004;134(3):568-573.

31.

Skov AR, Haulrik N, Toubro S, Molgaard C, Astrup A. Effect of protein intake on bone mineralization during weight loss: A 6-month trial. Obes Res. 2002;10(6):432-438.

32.

Thorpe MP, Jacobson EH, Layman DK, He X, Kris-Etherton PM, Evans EM. A diet high in protein, dairy, and calcium attenuates bone loss over twelve months of weight loss and maintenance relative to a conventional high-carbohydrate diet in adults. J Nutr. 2008;138(6): 1096-1100.

33.

Sukumar D, Ambia-Sobhan H, Zurfluh R, et al. Areal and volumetric bone mineral density and geometry at two levels of protein intake during caloric restriction: A randomized, controlled trial. J Bone Miner Res. 2011;26(6):1339-1348.

34.

Li Z, Treyzon L, Chen S, Yan E, Thames G, Carpenter CL. Proteinenriched meal replacements do not adversely affect liver, kidney or bone density: An outpatient randomized controlled trial. Nutr J. 2010;9:72.

35.

Noakes M, Keogh JB, Foster PR, Clifton PM. Effect of an energyrestricted, high-protein, low-fat diet relative to a conventional high-carbohydrate, low-fat diet on weight loss, body composition, nutritional status, and markers of cardiovascular health in obese women. Am J Clin Nutr. 2005;81(6):1298-1306.

36.

Josse AR, Atkinson SA, Tarnopolsky MA, Phillips SM. Diets higher in dairy foods and dietary protein support bone health during diet- and exercise-induced weight loss in overweight and obese premenopausal women. J Clin Endocrinol Metab. 2012;97(1):251-260.

7.

8.

9.

Layman DK, Boileau RA, Erickson DJ, et al. A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr. 2003;133(2): 411-417.

10.

Leidy HJ, Carnell NS, Mattes RD, Campbell WW. Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women. Obesity (Silver Spring). 2007;15(2):421-429.

11.

Farnsworth E, Luscombe ND, Noakes M, Wittert G, Argyiou E, Clifton PM. Effect of a high-protein, energy-restricted diet on body composition, glycemic control, and lipid concentrations in overweight and obese hyperinsulinemic men and women. Am J Clin Nutr. 2003;78(1):31-39.

12.

Heaney RP. Dairy and bone health. J Am Coll Nutr. 2009;28(suppl 1): 82S-90S.

13.

Conigrave AD, Brown EM, Rizzoli R. Dietary protein and bone health: Roles of amino acid-sensing receptors in the control of calcium metabolism and bone homeostasis. Annu Rev Nutr. 2008;28:131-155.

14.

Lutz J. Calcium balance and acid-base status of women as affected by increased protein intake and by sodium bicarbonate ingestion. Am J Clin Nutr. 1984;39(2):281-288.

15.

Sebastian A, Morris RC Jr. Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate. N Engl J Med. 1994;331(4):279.

16.

Kerstetter JE, Allen LH. Dietary protein increases urinary calcium. J Nutr. 1990;120:134-136.

37.

17.

Kerstetter JE, O’Brien KO, Insogna KL. Dietary protein affects intestinal calcium absorption. Am J Clin Nutr. 1998;68(4):859-865.

Barzel US, Massey LK. Excess dietary protein can adversely affect bone. J Nutr. 1998;128(6):1051-1053.

38.

18.

Schurch MA, Rizzoli R, Slosman D, Vadas L, Vergnaud P, Bonjour JP. Protein supplements increase serum insulin-like growth factor-I levels and attenuate proximal femur bone loss in patients with

Patience JF. A review of the role of acid-base balance in amino acid nutrition. J Anim Sci. 1990;68(2):398-408.

39.

Sellmeyer DE, Stone KL, Sebastian A, Cummings SR. A high ratio of dietary animal to vegetable protein increases the rate of bone loss

January 2014 Volume 114 Number 1

JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS

83

RESEARCH and the risk of fracture in postmenopausal women. Study of Osteoporotic Fractures Research Group. Am J Clin Nutr. 2001;73(1):118-122.

63.

Dawson-Hughes B. Interaction of dietary calcium and protein in bone health in humans. J Nutr. 2003;133(suppl 3):852S-854S.

40.

Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Protein consumption and bone fractures in women. Am J Epidemiol. 1996;143(5):472-479.

64.

41.

Bonjour JP. Dietary protein: An essential nutrient for bone health. J Am Coll Nutr. 2005;24(6 suppl):526S-536S.

Langdahl BL, Kassem M, Moller MK, Eriksen EF. The effects of IGF-I and IGF-II on proliferation and differentiation of human osteoblasts and interactions with growth hormone. Eur J Clin Invest. 1998;28(3):176-183.

65.

42.

Whiting SJ, Anderson DJ, Weeks SJ. Calciuric effects of protein and potassium bicarbonate but not of sodium chloride or phosphate can be detected acutely in adult women and men. Am J Clin Nutr. 1997;65(5):1465-1472.

Palmer G, Bonjour JP, Caverzasio J. Stimulation of inorganic phosphate transport by insulin-like growth factor I and vanadate in opossum kidney cells is mediated by distinct protein tyrosine phosphorylation processes. Endocrinology. 1996;137(11):4699-4705.

66.

43.

Frassetto LA, Morris RC Jr, Sebastian A. Effect of age on blood acidbase composition in adult humans: Role of age-related renal functional decline. Am J Physiol. 1996;271(6 pt 2):F1114-F1122.

Giustina A, Mazziotti G, Canalis E. Growth hormone, insulin-like growth factors, and the skeleton. Endocr Rev. 2008;29(5):535-559.

67.

Arjmandi BH, Khalil DA, Smith BJ, et al. Soy protein has a greater effect on bone in postmenopausal women not on hormone replacement therapy, as evidenced by reducing bone resorption and urinary calcium excretion. J Clin Endocrinol Metab. 2003;88(3):1048-1054.

68.

Langlois JA, Rosen CJ, Visser M, et al. Association between insulinlike growth factor I and bone mineral density in older women and men: The Framingham Heart Study. J Clin Endocrinol Metab. 1998;83(12):4257-4262.

69.

Rizzoli R, Bianchi ML, Garabedian M, McKay HA, Moreno LA. Maximizing bone mineral mass gain during growth for the prevention of fractures in the adolescents and the elderly. Bone. 2010;46(2): 294-305.

70.

Chevalley T, Rizzoli R, Manen D, Caverzasio J, Bonjour JP. Arginine increases insulin-like growth factor-1 production and collagen synthesis in osteoblast-like cells. Bone. 1998;23(2):103-109.

44.

Roughead ZK, Hunt JR, Johnson LK, Badger TM, Lykken GI. Controlled substitution of soy protein for meat protein: Effects on calcium retention, bone, and cardiovascular health indices in postmenopausal women. J Clin Endocrinol Metab. 2005;90(1):181-189.

45.

Kenny AM, Mangano KM, Abourizk RH, et al. Soy proteins and isoflavones affect bone mineral density in older women: A randomized controlled trial. Am J Clin Nutr. 2009;90(1):234-242.

46.

Massey LK. Dietary animal and plant protein and human bone health: A whole foods approach. J Nutr. 2003;133(3 suppl):862S865S.

47.

New SA. Intake of fruit and vegetables: Implications for bone health. Proc Nutr Soc. 2003;62(4):889-899.

48.

Heaney RP. Calcium, dairy products and osteoporosis. J Am Coll Nutr. 2000;19(2 suppl):83S-99S.

71.

49.

Howard JE. Calcium metabolism, bones and calcium homeostasis; a review of certain current concepts. J Clin Endocrinol Metab. 1957;17(9):1105-1123.

Cadogan J, Eastell R, Jones N, Barker ME. Milk intake and bone mineral acquisition in adolescent girls: Randomised, controlled intervention trial. BMJ. 1997;315(7118):1255-1260.

72.

50.

Hasling C, Charles P, Jensen FT, Mosekilde L. Calcium metabolism in postmenopausal osteoporosis: The influence of dietary calcium and net absorbed calcium. J Bone Miner Res. 1990;5(9):939-946.

Budek AZ, Hoppe C, Michaelsen KF, Bugel S, Molgaard C. Associations of total, dairy, and meat protein with markers for bone turnover in healthy, prepubertal boys. J Nutr. 2007;137(4):930-934.

73.

51.

Horowitz M, Need AG, Morris HA, Wishart J, Nordin BE. Biochemical effects of calcium supplementation in postmenopausal osteoporosis. Eur J Clin Nutr. 1988;42(9):775-778.

Larsson SC, Wolk K, Brismar K, Wolk A. Association of diet with serum insulin-like growth factor I in middle-aged and elderly men. Am J Clin Nutr. 2005;81(5):1163-1167.

74.

52.

Riggs BL, O’Fallon WM, Muhs J, O’Connor MK, Kumar R, Melton LJ 3rd. Long-term effects of calcium supplementation on serum parathyroid hormone level, bone turnover, and bone loss in elderly women. J Bone Miner Res. 1998;13(2):168-174.

Bonjour JP, Schurch MA, Chevalley T, Ammann P, Rizzoli R. Protein intake, IGF-1 and osteoporosis. Osteoporos Int. 1997;7(suppl 3): S36-S42.

75.

Nutrition and Your Health: Dietary Guidelines for Americans, 2005. 6th ed. Washington, DC: US Government Printing Office; 2005.

53.

Andon MB, Smith KT, Bracker M, Sartoris D, Saltman P, Strause L. Spinal bone density and calcium intake in healthy postmenopausal women. Am J Clin Nutr. 1991;54(5):927-929.

76.

Recker RR, Heaney RP. The effect of milk supplements on calcium metabolism, bone metabolism and calcium balance. Am J Clin Nutr. 1985;41(2):254-263.

54.

Cumming RG, Cummings SR, Nevitt MC, et al. Calcium intake and fracture risk: Results from the study of osteoporotic fractures. Am J Epidemiol. 1997;145(10):926-934.

77.

55.

Heaney RP. Calcium in the prevention and treatment of osteoporosis. J Intern Med. 1992;231(2):169-180.

Cheng S, Lyytikainen A, Kroger H, et al. Effects of calcium, dairy product, and vitamin D supplementation on bone mass accrual and body composition in 10-12-y-old girls: A 2-y randomized trial. Am J Clin Nutr. 2005;82(5):1115-1126.

78.

56.

Kerstetter JE, O’Brien KO, Insogna KL. Dietary protein, calcium metabolism, and skeletal homeostasis revisited. Am J Clin Nutr. 2003;78(3 suppl):584S-592S.

Gueguen L, Pointillart A. The bioavailability of dietary calcium. J Am Coll Nutr. 2000;19(2 suppl):119S-136S.

79.

Aoe S, Koyama T, Toba Y, Itabashi A, Takada Y. A controlled trial of the effect of milk basic protein (MBP) supplementation on bone metabolism in healthy menopausal women. Osteoporos Int. 2005;16(12):2123-2128.

80.

Uenishi K, Ishida H, Toba Y, Aoe S, Itabashi A, Takada Y. Milk basic protein increases bone mineral density and improves bone metabolism in healthy young women. Osteoporos Int. 2007;18(3):385-390.

81.

Christiansen P. The skeleton in primary hyperparathyroidism: A review focusing on bone remodeling, structure, mass, and fracture. APMIS Suppl. 2001;102:1-52.

57.

Kerstetter JE, O’Brien KO, Insogna KL. Low protein intake: The impact on calcium and bone homeostasis in humans. J Nutr. 2003;133(3 suppl):855S-861S.

58.

Kerstetter JE, O’Brien KO, Insogna KL. Dietary protein affects intestinal calcium absorption. Am J Clin Nutr. 1998;68(4):859-865.

59.

Kerstetter JE, O’Brien KO, Caseria DM, Wall DE, Insogna KL. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women. J Clin Endocrinol Metab. 2005;90(1):26-31.

82.

60.

Roughead ZK, Johnson LK, Lykken GI, Hunt JR. Controlled high meat diets do not affect calcium retention or indices of bone status in healthy postmenopausal women. J Nutr. 2003;133(4):1020-1026.

Heaney RP. The bone remodeling transient: Interpreting interventions involving bone-related nutrients. Nutr Rev. 2001;59(10):327-334.

83.

Hunt JR, Johnson LK, Fariba Roughead ZK. Dietary protein and calcium interact to influence calcium retention: a controlled feeding study. Am J Clin Nutr. 2009;89(5):1357-1365.

Elders PJ, Lips P, Netelenbos JC, et al. Long-term effect of calcium supplementation on bone loss in perimenopausal women. J Bone Miner Res. 1994;9(7):963-970.

84.

Heaney RP. The bone-remodeling transient: implications for the interpretation of clinical studies of bone mass change. J Bone Miner Res. 1994;9(10):1515-1523.

85.

Wahner HW, Dunn WL, Brown ML, Morin RL, Riggs BL. Comparison of dual-energy x-ray absorptiometry and dual photon absorptiometry for bone mineral measurements of the lumbar spine. Mayo Clin Proc. 1988;63(11):1075-1084.

61.

62.

84

Cao JJ, Johnson LK, Hunt JR. A diet high in meat protein and potential renal acid load increases fractional calcium absorption and urinary calcium excretion without affecting markers of bone resorption or formation in postmenopausal women. J Nutr. 2011; 141(3):391-397.

JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS

January 2014 Volume 114 Number 1

RESEARCH 86.

Prentice A, Parsons TJ, Cole TJ. Uncritical use of bone mineral density in absorptiometry may lead to size-related artifacts in the identification of bone mineral determinants. Am J Clin Nutr. 1994;60(6):837-842.

87.

Van Loan MD, Johnson HL, Barbieri TF. Effect of weight loss on bone mineral content and bone mineral density in obese women. Am J Clin Nutr. 1998;67(4):734-738.

88.

Yoganandan N, Pintar FA, Stemper BD, et al. Bone mineral density of human female cervical and lumbar spines from quantitative computed tomography. Spine (Phila Pa 1976). 2006;31(1):73-76.

89.

Villareal DT, Kotyk JJ, Armamento-Villareal RC, et al. Reduced bone mineral density is not associated with significantly reduced bone quality in men and women practicing long-term calorie restriction with adequate nutrition. Aging Cell. 2011;10(1):96-102.

AUTHOR INFORMATION M. Tang is a postdoctoral research associate, University of Colorado Denver; at the time of the study, she was a graduate student, Nutrition Science department, Purdue University, West Lafayette, IN. L. E. O’Connor is a research technician and W. W. Campbell is a professor of nutrition science, Department of Nutrition Science, Purdue University, West Lafayette, IN. Address correspondence to: Wayne W. Campbell, PhD, Department of Nutrition Science, Purdue University, 700 W State St, West Lafayette, IN 47907. E-mail: [email protected]

STATEMENT OF POTENTIAL CONFLICT OF INTEREST No potential conflict of interest was reported by the authors.

FUNDING/SUPPORT There is no funding to disclose.

January 2014 Volume 114 Number 1

JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS

85