Effect of soy protein diet versus standard low fat, low cholesterol diet on lipid and lipoprotein levels in children with familial or polygenic hypercholesterolemia

Effect of soy protein diet versus standard low fat, low cholesterol diet on lipid and lipoprotein levels in children with familial or polygenic hypercholesterolemia Kurt W i d h a l m , MD, G a b r i e l e Brazda, Dipi DiOtass, B a r b a r a S c h n e i d e r , Dipl Ing Dr techn, a n d Susanne Kohl, MD From the Department of Pediatrics and the Institute for Medical Statistics, University of Vienna, Vienna, Austria

The effect on serum lipid and lipoprotein levels of a standard low fat, low cholesterol diet was compared with that of a soy protein-substituted low fat, low cholesterol diet in 23 children with familial or polygenic hypercholesterolemia: 12 boys and 11 girls (mean age, 9.3 _+ 4.5 years) were included in this outpatient program. Group I received the soy protein diet for8 weeks; group 2 received the low fat, low cholesterol diet. After an interruption of 8 weeks, each group was p l a c e d on the alternate regimen. Fasting blood samples were collected at the beginning of each dietary period. During the soy protein diet, the levels of total cholesterol decreased by 16% in group I and 18% in group 2, and low-density lipoprotein cholesterol (LDL-C) levels decreased about 22% in group 1 and 25% in group 2. During the standard low fat, low cholesterol diet, total cholesterol and LDL-C levels were reduced by 8% and 7% in group I and by 12% and 13%, respectively, in group 2. The effect on LDL-C was significantly greater (p <0.05) in the soy protein group than in the low fat, low cholesterol group. We conclude that a diet substituting soy protein for animal protein has a more beneficial short-term effect on total cholesterol and LDL-C levels in children with hypercholesterolemia than a standard low fat diet. (J PEDIATR1993;123:30-4)

Familial hypercholesterolemia, a common disorder of lipoprotein metabolism in childhood, is characterized by significant elevation of low-density lipoprotein and total cholesterol levels. Usually there are two therapeutic strategies to reduce elevated plasma cholesterol levels: diet and drug treatment; especially in children, all possibilities of dietary treatment should be utilized to avoid long-term drug therapy. It is widely accepted that elevated LDL-C levels are associated With an increased risk of premature atherosclerotic lesions. The affected patients have a high risk of mySubmitted for publication Feb. 13, 1993;accepted March 16, 1993. Reprint requests: K. Widhalm, MD, University of Vienna, Mautnet Markhof Children's Hospital, Baumgasse 75, A-1030 Vienna, Austria. Copyright | 1993 by Mosby-Year Book, Inc. 0022-3476/93/$1.00 + .10 9/22/47232

30

ocardial infarction in the fourth or fifth decade of their lives and markedly increased morbidity and mortality rates because Of premature coronary artery disease. 1'2 Primary prevention of atherosclerotic disease should start as early as See related article, p. 24.

FH HDL HDL-C LDL LDL-C TC

Familial hypercholesterolemia High-density lipoprotein High-density lipoprotein-cholesterol Low-density lipoprotein Low-density lipoprotein-cholesterol Total cholesterol

2 years of age, as recommended by the American Academy of Pediatrics) Elevated TC and LDL-C levels should first be lowered by diet; if diet is not successful, drug treatment

The Journal o f Pediatrics Volume 123, Number 1

should be considered. There are some concerns on the part of pediatricians about using long-term cholesterol-lowering drug treatment; no studies have shown that long-term drug treatment is harmless to growth or development. We investigated the effect of a standard low fat, low cholesterol diet, in comparison with the effect of a diet enriched with soy protein, on lipid and lipoprotein levels in children with heterozygous F H or a polygenic hypercholesterolemia. The mechanism of the cholesterol-lowering effect of a soy protein diet is not clear, so we measured not only lipid and lipoprotein levels but also apolipoprotein B levels to evaluate a possible change in the composition of the atherogenic LDL particle. METHODS

Patients and study design. Twelve boys and eleven girls (mean age, 9.3 _+ 4.5 years) entered this outpatient program; 19 of these children came from families in which at least one parent had hypercholesterolemia, with TC and LDL-C levels above the 90th percentile according to the Lipid Research Clinics protocol. 4 Polygenic hypercholesterolemia was diagnosed in four children. The study was divided into three sections of 8 weeks each. Group I started with an 8-week period of the soy proteinsubstituted diet; group II received a standard low fat, low cholesterol diet (Table I). After a break of 2 months, each group was given the alternate diet. Dietary plans were carefully explained to all families by a dietitian. To improve adherence to the therapy, we inspected afterward the records of intake written by the parents and children during a period of at least 7 days. No weight changes were observed during either dietary period. Procedures. Fasting blood samples were drawn from antecubital veins at the beginning and end of each dietary period, and weight and height were measured. Cholesterol and triglyceride levels were measured enzymatically by using test kits from Boehringer Mannheim Gmbh (Mannheim, Germany): CHOD-PAP and GPO-PAP (enzymatic calorimetric methods), respectively. For determinations of LDL-C and HDL-C, with subclasses HDL3 and HDL2, we used a precipitation method with polyethylene glycol in different concentrations 5 (Quantolip; Immuno Diagnostics, Vienna, Austria). External quality control was performed in cooperation with the World Health Organization Reference Programmes (the World Health Organization Collaborating Lipid Reference Center, Institute for Clinical and Experimental Medicine, Prague, Czechoslovakia) with excellent results (our average bias at the end of 1991 was -2.5% for cholesterol, -1.1% for triglycerides, and +3.6% for HDL-C). Very low density lipoproteins were removed by ultracentrifugation6; we used a model L7-65 ultracentrifuge (Beckman Instruments, Palo Alto, Calif.) with a

W i d h a l m et al.

31

T a b l e I. Diet compositions during both dietary regimens

Diet composition

Standard low fat, low cholesterol diet

Soy protein diet*

Protein (%)? 15 18 Fat (%)? 35 32 Carbohydrates (%)? 50 50 Daily cholesterol intake ~ 190 ~ 140 (nag) Polyunsaturated fatty 14.8 12.5 acids (gin) Saturated fatty 22.7 17.1 acids (gin) P/S ratio 0.65 0.73 P/S, Polyunsaturated/saturated(fatty acids]. *Soybeanflour (Purina Mills,St. Louis,Mo.), approximately15 to 20 gm per day. tPereentage of total en.ergyintake.

fixed-angle rotor 50.4 Titan at 40,000 rpm (105,000g) for 18 hours. Apolipoprotein B was measured by nephelometry with test kits from Boehringer Mannheim. 9Statistical analysis. Values are expressed as means _+ SD. The significance criterion was p <0.05. Analysis of significance was performed by using the Wilcoxon signed rank test for paired data. For numeric and graphic analysis, we used the Statistical Analysis Systems software package (SAS Institute Inc., Cary, N.C.). RESULTS During both diets, significant reductions of TC, LDL-C, and apolipoprotein B levels were observed. The comparison of the diet values showed significant differences in the TC, LDL-C, and apolipoprotein B values but none in the HDL values. During the soybean diet, whether given before or after the standard low lipid diet, a more pronounced reduction of TC, LDL-C, and apolipoprotein B levels was observed (Table II). The mean decrease in plasma cholesterol values with soy protein was 16% in group 1 and 18% in group 2; LDL-C levels decreased about 22% in group 1 and 25% in group 2. The HDL-C level did not change significantly in either group. Group 1, however, had a significant decrease in the T C / H D L - C ratio; the T C / H D L - C ratio in group 2 also dropped during the soybean diet (Table II). In comparison with these results, during the low fat, low cholesterol diet in group l, only a decrease in TC of 8% and in LDL-C of about 7% could be achieved; group 2 had a decrease in TC up to 12% and in LDL-C up to 13%. In both groups, HDL-C levels did not change significantly. According to the Wilcoxon signed rank test, the LDL-C level was lowered to a significantly (p <0.05) greater degree in the soy protein group than in the low fat diet group. Moreover, no change in body weight could be observed

32

W i d h a l m et al.

The Journal of Pediatrics July 1993

Table II. Lipids, lipoproteins and apolipoprotein B in children with hypercholesterolemia on two different diet regimens: a soy-protein diet and a standard low fat, low cholesterol diet

Group I (n = 13) Standard diet

Soy protein diet Lipid (mg/dl) TC LDL-C HDL-C Apo B TC/HDL-C HDL2-C HDL3-C

Begin 230.7 174 45.6 99.7 5.3 10.4 35.2

_+ 33.4 • 27.8 • 10.2 _+ 12.7 • 1.3 _+ 5 _+ 8.2

End 194.2 135.5 45.2 80 4.4 8.4 36.8

Change (%)

• 33.8I" • 31~: -+ 8.4 • 17.1I" • 1" • 2.7 • 6.5

-16 -22 -1 -19 -16 -19 +5

Begin 213.4 156.8 47.6 89.4 4.6 10.3 37.3

• • • • • • •

35.6 36.6 8.4 16.7 1.1 3.5 7.2

End 197.3 145.2 45.4 78.6 4.5 9.2 36.2

• 21.9 • 27.1 _+ 9 +_ 13.27 +_ 1.2 _+ 3.1 _+ 8.3

Change (%) -8 -7 -5 -12 -2 -11 -3

The subjects in both groups followedtheir own habitual diets in the interval between their first study diet and their alternate diet. Lipid values were assessed at the end of interval. Apo B, ApolipoproteinB. *p <0.05. tP < 0.005. ~p < 0.001. during each dietary period. A sustained effect of the soy protein diet was observed: some pretreatment values were significantly reduced after the interval of habitual diet in group 1. After experiments in our diet kitchen, we succeeded in producing a considerable number of tasty dishes from soy protein. I t c a n be added to doughs for bread and pizzas and to milkshakes and fruit drinks. All families participating in the program received a comprehensive collection of recipes and had no problems in administering soy protein. The quantity of 15 to 20 gm soy protein per day was well accepted by the children. Most of them decided to take it in fruit drinks. Pure soy protein is similar to flour in character and is rejected if served in its pure state. DISCUSSION Several authors have shown that the partial substitution of soy proteins for animal protein in a moderately low fat diet significantly reduces plasma cholesterol levels in young outpatients with stable type II hypercholesterolemia. However, reports of the clinical efficacy and mode of action of diets in which vegetable protein is partially or totally substituted for animal protein have been controversial. In particular, normocholesterolemic subjects given soy protein isolates (generally with a diet low in polyunsaturated and saturated fatty acids) have slight 7 or insignificant 8 reduction of plasma cholesterol values. In 1977, Sirtori et al. 9 reported on 22 patients with F H who, after receiving a standard low fat, low cholesterol diet for 3 weeks, received a diet in which soy protein was totally substituted for animal protein. No cholesterol-lowering effect could be achieved during the standard low fat, low cholesterol diet, but during the soy protein diet the plasma

cholesterol levels were reduced by about 21%. Descovich et al. I~ showed a significant reduction of total cholesterol levels in 121 outpatients during a soy protein diet compared with a standard low fat, low cholesterol diet. Glueck et a1.11 prescribed a low fat, low cholesterol diet for 2- to 7-year-old children and described a cholesterol reduction of 6% to 15%. In none of the children with F H was normalization of the cholesterol level achieved. All these dietary regimens were accompanied by a moderate decrease (10%) in T C and L D L - C levels during the low fat, low cholesterol diet. On the other hand, the marked cholesterol-lowering effect of a soy protein-substituted diet (20%) has been noted in adults with hypercholesterolemia. 12 As far as we know, only one other report 13 evaluates the effect of a soy protein diet in children with FH: Gaddi and Descovic 14 investigated the effect of a soy protein-substituted diet in 16 children with F H and reported a cholesterol-lowering effect of 21.8% after an 8-week treatment period. The selection of patients and the type of dietary proteins administered may explain the differences between our data and those reported previously. Compared with the wealth of knowledge about adult hypercholesterolemia, little is known about the specific sensitivity of children to dietary changes. Both infants t5 and young children t3 seem to respond to dietary cholesterol and fat restriction, generally showing significant plasma cholesterol reduction after shifting from a diet containing >400 mg cholesterol per day to a diet with <150 m g / d a y . ~3 The effect are, however, far less striking in children with hypercholesterolemia who are older than 6 years of age. Rose et al. ~6 reported a 20% reduction in serum cholesterol levels in only half of the children with type II hypercholesterolemia. In 1981, children with type II hypercholesterolemia were treated by Fernandes et al. 17 with a vir-

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W i d h a l m et al.

33

Table II. Cont'd Group 2 (n = 10) Soy protein diet

Standard diet Begin 218.2 163.4 47.3 107.3 4.8

• • • • +

34.5 22.6 13.4 20.3 1.0

End 191.9 143.1 47.9 99.8 4.1

• 33.2* _+ 27.2* _+ 12.2 _+ 17.2 • 0.9

Change (%) -12 -13 +1 -7 -14

tually cholesterol-free vegetarian diet with a high linoleic acid content and 39% of total energy intake from vegetable protein, compared with 33% in the reference low lipid diet; the mean cholesterol reduction induced was approximately 10%. Our previous results in children with hypercholesterolemia who consumed a soybean-substituted diet showed a reduction of 32% in T C levels and 37% in L D L - C levels. 9 In our present study the most pronounced effects were on the L D L fraction (decrease of 25 %) and on the reduction of T C levels. Moreover, the c h o l e s t e r o l / H D L ratio in both groups dropped significantly during the soy protein diet. The apolipoprotein B levels decreased concomitantly to the L D L - C levels. The mechanism of the cholesterol-lowering effect of diets with soy protein substituted for animal protein is not fully understood, but several explanations have been offered. West 18 concluded that the differences between the effects on plasma cholesterol levels of the plant proteins and their corresponding amino acid mixtures were related to factors involved in the digestion of the proteins and absorption of their constituent amino acids. Moreover, Huff and Carroll 19 detected that, after intravenous injection of cholesterol into rabbits fed cholesterol-free, semipurified diets containing soy protein, the plasma cholesterol turnover (catabolism) was more rapid than in casein-fed rabbits; more of the neutral sterols and bile acids were excreted by the soy-fed animals than by the casein-fed animals. Studies of the absorption of cholesterol from the gut indicated that it is absorbed better by rabbits fed casein than by those fed soy protein) 9 Overall, it appears that the mechanisms for both the catabolism and the excretion of cholesterol are more effective in rabbits fed soy protein than in those fed casein, but it is still not clear whether the intestinal tract is the main regulating site of cholesterol metabolism by dietary proteins. Lovati et al. 2~ reported increased LDL-receptor activity in patients with type II hypercholesterolemia who were treated with a soy protein

Begin 227.2 172.5 52.1 110.5 4.5

• 29.1 _+ 28.8 • 12.5 • 25.7 • 1.0

End 185 128.1 45.1 83.2 4.2

+ 25.5~: _+ 21:~ • 8.8 • 18.4t ___0.6

Change (%) -18 -25 -13 -25 -7

diet, which could explain the additional cholesterol-lowering effect of soy protein. Genetic hypercholesterolemia persists throughout life. Thus it is important to adhere to a lifelong cholesterol-lowering diet. It also seems justified to lower the blood cholesterol levels of the general population to reduce the high incidence of cardiovascular disease. This population approach, as a public health strategy through adoption of a prudent diet, should include children. Children with hypercholesterolemia whose families are at high risk for cardiovascular disease should start a carefully monitored diet as soon as possible (for practical reasons, between approximately 4 and 6 years of age). The soy protein diet may offer an important contribution to diet therapy for F H in childhood. Special dietary instruction and close supervision will ensure a more pronounced reduction of T C and L D L - C levels in comparison with that obtained with a standard low fat, low cholesterol diet. The low cost of this vegetable protein is a further benefit. REFERENCES

1. Lipid Research Clinics Coronary Primary Prevention Trial. Results. I. Reduction in incidence of coronary disease. JAMA 1984;251:351-64, 2. Lipid Research Clinics Coronary Primary Prevention Trial. Results. II. The relationship of reduction in incidence of coronary heart disease to cholesterol lowering. JAMA 1984; 25l:365-74. 3. American Academy of Pediatrics Committee on Nutrition. Childhood diet and coronary heart disease. Pediatrics 1972; 49:305-7. 4. Lipid Research Clinics Program. Lipid Research Clinics population data book; vol 1. The prevalence study. Washington, D.C.: U.S. Department of Health and Human Services, 1980; publication No. (NIH) 1980;80:1527. 5. Widhalm K, Pakosta R. Precipitation with polyethylene glycol and density-gradient ultracentrifugation compared for determining high-density lipoprotein subclasses HDL2 and HDL3. Clin Chem 1991;37:238-40, 48. 6. Widhalm K, Maxa E, Zyman H. Effect of diet and exercise

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upon the cholesterol and triglyceride content of plasma lipoproteins in overweight children. Eur J Pediatr 1978;127: 121-6. Carroll KK, Giovanetti PM, Huff MW, Moore O, Roberts DCK, Wolfe BM. Hypocholesterolemic effect of substituting soybean protein for animal protein in the diet of healthy young women. Am J Clin Nutr 1978;31:1320-1. Van Raaij JMA, Katan MB, West CE, Hautvast JGAJ. Influence of diets containing casein, soy isolate and soy concentrate on serum cholesterol and lipoproteins in middleaged volunteers. Am J Clin Nutr 1982;35:925-34. Sirtori CR, Agradi E, Conti F, Mantero O, Gatti E. Soybeanprotein diet in the treatment of type-II hypercholesterolemia. Lancet 1977;1:275-7. Descovich GC, Gaddi A, Mannino G, et al. Multicentre study of soybean-protein diet for outpatient hypercholesterolemic patients. Lancet 1980;2:709-12. Glueck C J, Reginald C, Tsang R, Ronald W, Fallat R, Mellies MJ. Diet in children heterozygous for familial hypereholesterolemia. Am J Dis Child 1977;131:162-6. Schlierf G, Vogel G, Heuck CC, Oster P, Raetzer H, Schellenberg B. Dietary management for familial hypercholesterolemia in children and adolescents: feasibility study. Monatsschr Kinderheilkd 1977;125:770-3. Widhalm K. Pediatric guidelines for lipid reduction. Eur Heart J 1987;8:65-70.

14. Gaddi A, Descovic GC. Hypercholesterolemia treated by soybean diet. Arch Dis Child 1987;62:274-8. 15. Tsang RC, Glueck CJ, Fallat RW, Mellies M. Neonatal familial hypercholesterolemia. Am J Dis Child 1975; 129:8391. 16. Rose V, Allen DM, Pearse RG, Chapell J. Primary hyperlipoproteinemia in childhood and adolescence: identification and treatment of persons at risk for premature atherosclerosis. Can Med Assoc J 1976;115:753-7. 17. Fernandes J, Dijkhuis-Stoffelsma R, Groot PHE, Grose WFA, Ambaptsheer JJ. The effect of a virtually cholesterol-free, high linoleic acid vegetarian diet on serum tipoproteins of children with hypercholesterolemia (type IIa). Acta Paediatr Scand 1981;70:677-82. 18. West CE, Beynen AC, Terpstra AHM, Scholz KE, Carroll KK, Woodward CJH. The nature of dietary protein and serum cholesterol. Atherosclerosis 1983;46:253-6. 19. Huff MW, Carroll KK. Effects of dietary protein on turnover, oxidation and absorption of cholesterol and on steroid excretion in rabbits. J Lipid Res 1980;21:546-8. 20. Lovati MR, Manzoni C, Canavesi A, et al. Soybean protein diet increases low density lipoprotein receptor activity in mononuclear cells from hypercholesterolemic patients. J Clin Invest 1987;80:1498-502.

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