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Oxalate content of selected pasta products
Journal of Food Composition and Analysis 22 (2009) 254–256
Contents lists available at ScienceDirect
Journal of Food Composition and Analysis journal homepage: www.elsevier.com/locate/jfca
Short Communication
Oxalate content of selected pasta products Michael Liebman *, Joseph Okombo Department of Family and Consumer Sciences (Human Nutrition), University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071, USA
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 May 2008 Received in revised form 16 September 2008 Accepted 20 October 2008
About 75% of kidney stones are composed primarily of calcium oxalate, and hyperoxaluria is a primary risk factor for this disorder. Since pasta products are widely consumed and absorbed dietary oxalate can make a significant contribution to urinary oxalate levels, the oxalate content of various types of pasta was analyzed using an enzymatic method. The majority of pasta products had total oxalate contents that ranged from 20 to 30 mg/100 g wet weight and soluble oxalate contents that ranged from 5 to 12 mg/ 100 g. Products lowest in total oxalate were spaghetti and brown rice pasta. Pasta products that contained vegetable powders among the listed ingredients were highest in oxalate, and the proportion of spinach powder in these samples was an important determinant of oxalate content. The overall data suggested that most types of pasta are at least moderately high in oxalate. ß 2009 Elsevier Inc. All rights reserved.
Keywords: Dietary oxalate Soluble oxalate Insoluble oxalate Pasta Semolina flour Kidney stones Food analysis Food composition
1. Introduction Approximately 75% of all kidney stones are composed primarily of calcium oxalate (Williams and Wandzilak, 1989), and hyperoxaluria is a key risk factor for this disorder (Goldfarb, 1988; Robertson and Hughes, 1993). Because urinary oxalate originates from a combination of absorbed dietary oxalate and endogenously synthesized oxalate (Williams and Wandzilak, 1989), restriction of dietary oxalate has been suggested as a means to prevent recurrent nephrolithiasis in some patients (Massey et al., 1993). Plants and plant products are the main sources of dietary oxalate (Noonan and Savage, 1999). Plant tissues contain soluble oxalate sources such as sodium and potassium oxalate as well as insoluble oxalate salts such as calcium and magnesium oxalate (Savage et al., 2000). The efficiency of oxalate absorption (i.e., oxalate bioavailability) is an important determinant of whether a particular food can significantly increase urinary oxalate excretion (Brinkley et al., 1990). The amount of soluble oxalate in a food is also important because it appears to be more bioavailable than insoluble oxalate (Chai and Liebman, 2004; Tang et al., 2008). Different types of pasta products, typically made primarily from Durum wheat flour (also known as semolina flour) but sometimes incorporating other ingredients, are commonly consumed in many countries. Although we have previously reported the oxalate
* Corresponding author. Tel.: +1 307 766 5597; fax: +1 307 766 5686. E-mail address: [email protected] (M. Liebman). 0889-1575/$ – see front matter ß 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2008.10.013
content of different types of flour products (Chai and Liebman, 2005a), comprehensive reports of oxalate concentrations in pasta products have not been published. Thus, the purpose of the present study was to determine both the total and soluble oxalate content of various types of commercially available pastas.
2. Materials and methods 2.1. Samples and sample preparation The following types of pasta products were assessed for both total and soluble oxalate: spaghetti (three different brands), lasagne (two brands), penne pasta (three brands), macaroni (three brands), egg noodles (two brands), brown rice pasta (three brands), vegetable-pasta blends (three brands), and five different types of whole wheat pastas. All pasta products were purchased from local establishments in Laramie, Wyoming. Pasta samples were boiled in water for the time periods specified on the package; boiling times ranged from 7 min (egg noodles pasta) to 20 min (one of the lasagna samples). After boiling, samples were drained in a colander for 2 min, weighed, frozen at 25 8C for approximately 24 h, and then freeze-dried (Freezemobile 6, Virtis Company, Gardiner, NY) for approximately 48 h to achieve a constant dry weight. Freezedried samples were initially ground with a mortar and pestle and then in a Pavoni coffee mill until the particles could not be further homogenized. Since the primary ingredient for the majority of pasta samples tested was semolina flour, which is obtained from
M. Liebman, J. Okombo / Journal of Food Composition and Analysis 22 (2009) 254–256
grinding Durum wheat, we also analyzed the oxalate content of a commercially available brand of semolina flour. 2.2. Total and soluble oxalate extraction Total and soluble oxalates were extracted according to a previously described method (Ross et al., 1999). Duplicate finely ground pasta samples (or semolina flour samples) ranging from 1.5 to 1.8 g were weighed into 500 mL beakers after which 50 mL of 2 M H3PO4 (for total oxalate) or 50 mL of distilled deionized water (for soluble oxalate) was added. The contents were then mixed, beakers covered with aluminum foil, and then placed in a shaking water bath at 80 8C for 30 min. After cooling and bringing the volumes up to 100 mL with distilled deionized water, the diluted extractions were centrifuged at 3000 rpm for 10 min and the supernatants were filtered through Whatman number 1 filter paper. 2.3. Oxalate analysis Oxalate from filtered pasta and semolina flour samples were measured in duplicate by using an oxalate kit obtained from Trinity Biotech (Jamestown, NY). The method is based on the oxidation of oxalate by oxalate oxidase followed by detection of H2O2 produced during the reaction (Li and Madappally, 1989). Lyophilized (control) urine samples (Trinity Biotech, Jamestown, NY) providing predetermined oxalate levels of 20–30 mg/L were analyzed with each assay to ensure good quality control. 3. Results and discussion Mean (S.D.) values for total and soluble oxalate contents of various pasta products are given in Table 1. The difference between total and soluble oxalate values presented in this table represents insoluble oxalate. Knowing the proportion of total oxalate that is
255
soluble is potentially important because of the presumed higher bioavailability of soluble as compared to insoluble oxalate (Chai and Liebman, 2004; Tang et al., 2008). The results indicated that the majority of pasta products would be considered to be foods of moderate oxalate content, as the majority of samples had total oxalate contents that ranged from 20 to 30 mg/100 g wet weight and soluble oxalate contents that ranged from 5 to 12 mg/100 g. The semolina flour samples that we tested had total and soluble oxalate contents of 66.6 3.8 and 32.6 1.6 mg/100 g, respectively. Kidney stone patients who form calcium-oxalate containing stones are advised to limit their intake of foods which contain >10 mg oxalate per serving, with total oxalate intake not to exceed 50–60 mg/ day (Chicago Dietetic Association, 2000). Assuming that a 1 cup serving of pasta weighs approximately 100 g, it is clear that consumption of these foods could make a significant contribution to an individual’s total oxalate intake and would need to be limited in those following low-oxalate diets. There were variations in the oxalate content of different types of pasta that could be clinically important. The types of pasta that were lowest in total oxalate were spaghetti products (overall mean of 14.0 mg/100 g for the three different brands) and brown rice pasta (overall mean of 12.3 mg/100 g). Among the non-vegetablepasta blends, lasagne had the highest total oxalate content (overall mean of 27.5 mg/100 g for two different brands). With respect to the vegetable-pasta blends, the two that contained combinations of tomato, beet, and spinach powders in addition to flour had an overall mean of 38.7 mg oxalate/100 g. The spinach fettuccine, which contained spinach powder and Jerusalem artichoke flour, in addition to Durum semolina flour, had an oxalate content of 91.8 mg/100 g. Since spinach is known to be a very high oxalate food, with reported values as high as 1145 mg/100 g wet weight (Chai and Liebman, 2005b), it is not surprising that the proportion of spinach powder in the vegetable-pasta blends was an important determinant of the total oxalate content of these samples.
Table 1 Oxalate content of different types of pastaa. Pasta
Brand
Oxalate content (mg/100 g wet weight) Total
Moisture content (g/100 g wet weight)
Soluble
Spaghetti
1 2 3
15.6 0.5 13.7 0.4 12.7 0.1
6.6 1.1 4.1 1.3 8.3 0.8
66.4 71.2 70.7
Penne
1 2 3
25.0 0.3 23.2 1.0 22.9 0.5
6.4 1.2 7.8 0.1 9.8 0.5
63.0 61.5 59.3
Macaroni
1 2 3
19.7 0.1 26.1 1.1 20.6 1.5
3.8 0.7 10.1 1.4 4.9 0.4
69.9 66.7 63.4
Brown rice
1 2 3
10.2 0.6 12.3 0.7 14.3 1.5
2.8 0.1 2.3 0.4 2.4 0.2
63.0 61.0 67.6
Lasagne
1 2
26.4 1.6 28.5 0.1
11.7 0.9 11.5 0.6
63.1 52.8
Egg noodles
1 2
24.4 1.6 27.3 0.1
9.2 0.8 12.6 0.3
63.8 57.6
Whole wheat varieties
1 2 3 4 5
20.6 1.9 22.0 0.1 31.3 1.7 24.5 0.1 22.1 1.6
8.4 0.8 6.3 0.4 11.1 0.8 10.7 0.7 8.1 0.8
71.4 63.1 62.6 65.2 65.2
Vegetable blend
1 2
40.6 2.3 36.8 0.5
21.5 0.6 20.9 0.6
68.0 61.0
Spinach fettuccine
1
91.8 2.4
53.8 0.7
60.7
a
Sample n = 2; wet weight refers to cooked and drained weight.
256
M. Liebman, J. Okombo / Journal of Food Composition and Analysis 22 (2009) 254–256
The five whole wheat pasta samples had oxalate contents that ranged from 20.6 to 31.3 mg/100 g. The two samples with the highest oxalate levels (24.5 and 31.3 mg/100 g, respectively) both included wheat bran among the list of ingredients. These higher oxalate values can be attributed to our previously unpublished observation that wheat bran is a high-oxalate food component that contains approximately 84 mg oxalate/100 g. The remaining whole wheat pasta samples did not have higher oxalate levels than many of the other types of pasta such as penne, macaroni, lasagne, and egg noddles. This can be explained by pointing out that semolina flour, which we found in the present study to contain 67 mg oxalate/100 g, is virtually identical in oxalate content to our previously reported value for whole wheat flour (Chai and Liebman, 2005a). The oxalate levels reported in the present study are considerably higher than those that appear in the literature from other laboratories (Kasidas and Rose, 1980; Brezinski et al., 1996), but are not surprising in light of the oxalate values previously reported for various flour products (Chai and Liebman, 2005a) as well as the currently reported value for semolina flour. It should be acknowledged that the ability of various oxalate-containing foods to increase urinary oxalate excretion depends on both oxalate content and bioavailability. Thus, it is also important for future studies to determine the oxalate bioavailability of various pasta products, particularly those that are highest in oxalate.
Acknowledgment This study was supported by a grant from The VP Foundation, Graham, North Carolina.
References Brezinski, E., Durning, A.M., Grasse, B., Fusselman, E., Ciaraldi, T., 1996. Oxalate Content of Selected Foods. San Diego Medical Center, University of California. Brinkley, L.J., Gregory, J., Pak, C.Y.C., 1990. A further study of oxalate bioavailability in foods. Journal of Urology 144, 94–96. Chai, W., Liebman, M., 2004. Assessment of oxalate absorption from almonds and black beans with and without the use of an extrinsic label. Journal of Urology 172, 953–957. Chai, W., Liebman, M., 2005a. Oxalate content of legumes, nuts, and grain-based flours. Journal of Food Composition and Analysis 18, 723–729. Chai, W., Liebman, M., 2005b. Effect of different cooking methods on vegetable oxalate content. Journal of Agricultural and Food Chemistry 53, 3027–3030. Chicago Dietetic Association, 2000. Manual of Clinical Dietetics. American Dietetics Association, Chicago, IL, p. 475. Goldfarb, S., 1988. Dietary factors in the pathogenesis and prophylaxis of calcium nephrolithiasis. Kidney International 34, 544–555. Kasidas, G.P., Rose, G.A., 1980. Oxalate content of some common foods: determination by an enzymatic method. Journal of Human Nutrition 34, 255–266. Li, M.G., Madappally, M.M., 1989. Rapid enzymatic determination of urinary oxalate. Clinical Chemistry 35, 2330–2333. Massey, L.K., Roman-Smith, H., Sutton, R.A.L., 1993. Effect of dietary oxalate and calcium on urinary oxalate and risk of formation of calcium oxalate kidney stones. Journal of the American Dietetic Association 93, 901–906. Noonan, S.C., Savage, G.P., 1999. Oxalate content of foods and its effect on humans. Asia Pacific Journal of Clinical Nutrition 8, 64–74. Robertson, W.G., Hughes, H., 1993. Importance of mild hyperoxaluria in the pathogenesis of urolithiasis—new evidence from studies in the Arabian peninsula. Scanning Microscopy 7, 391–401. Ross, A.B., Savage, G.P., Martin, R.J., Vanhanen, L., 1999. Oxalate in oca (New Zealand yam) (Oxalis tuberosa Mol.). Journal of Agricultural and Food Chemistry 47, 5019–5022. Savage, G.P., Vanhanen, L., Mason, S.M., Ross, A.B., 2000. Effect of cooking on the soluble and insoluble oxalate content of some New Zealand foods. Journal of Food Composition and Analysis 13, 201–206. Tang, M., Larson-Meyer, D.E., Liebman, M., 2008. Effect of cinnamon and turmeric on urinary oxalate excretion, plasma lipids and plasma glucose in healthy subjects. American Journal of Clinical Nutrition 87, 1262–1267. Williams, H.E., Wandzilak, T.R., 1989. Oxalate synthesis, transport and the hyperoxaluric syndromes. Journal of Urology 141, 742–747.
Contents lists available at ScienceDirect
Journal of Food Composition and Analysis journal homepage: www.elsevier.com/locate/jfca
Short Communication
Oxalate content of selected pasta products Michael Liebman *, Joseph Okombo Department of Family and Consumer Sciences (Human Nutrition), University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071, USA
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 May 2008 Received in revised form 16 September 2008 Accepted 20 October 2008
About 75% of kidney stones are composed primarily of calcium oxalate, and hyperoxaluria is a primary risk factor for this disorder. Since pasta products are widely consumed and absorbed dietary oxalate can make a significant contribution to urinary oxalate levels, the oxalate content of various types of pasta was analyzed using an enzymatic method. The majority of pasta products had total oxalate contents that ranged from 20 to 30 mg/100 g wet weight and soluble oxalate contents that ranged from 5 to 12 mg/ 100 g. Products lowest in total oxalate were spaghetti and brown rice pasta. Pasta products that contained vegetable powders among the listed ingredients were highest in oxalate, and the proportion of spinach powder in these samples was an important determinant of oxalate content. The overall data suggested that most types of pasta are at least moderately high in oxalate. ß 2009 Elsevier Inc. All rights reserved.
Keywords: Dietary oxalate Soluble oxalate Insoluble oxalate Pasta Semolina flour Kidney stones Food analysis Food composition
1. Introduction Approximately 75% of all kidney stones are composed primarily of calcium oxalate (Williams and Wandzilak, 1989), and hyperoxaluria is a key risk factor for this disorder (Goldfarb, 1988; Robertson and Hughes, 1993). Because urinary oxalate originates from a combination of absorbed dietary oxalate and endogenously synthesized oxalate (Williams and Wandzilak, 1989), restriction of dietary oxalate has been suggested as a means to prevent recurrent nephrolithiasis in some patients (Massey et al., 1993). Plants and plant products are the main sources of dietary oxalate (Noonan and Savage, 1999). Plant tissues contain soluble oxalate sources such as sodium and potassium oxalate as well as insoluble oxalate salts such as calcium and magnesium oxalate (Savage et al., 2000). The efficiency of oxalate absorption (i.e., oxalate bioavailability) is an important determinant of whether a particular food can significantly increase urinary oxalate excretion (Brinkley et al., 1990). The amount of soluble oxalate in a food is also important because it appears to be more bioavailable than insoluble oxalate (Chai and Liebman, 2004; Tang et al., 2008). Different types of pasta products, typically made primarily from Durum wheat flour (also known as semolina flour) but sometimes incorporating other ingredients, are commonly consumed in many countries. Although we have previously reported the oxalate
* Corresponding author. Tel.: +1 307 766 5597; fax: +1 307 766 5686. E-mail address: [email protected] (M. Liebman). 0889-1575/$ – see front matter ß 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2008.10.013
content of different types of flour products (Chai and Liebman, 2005a), comprehensive reports of oxalate concentrations in pasta products have not been published. Thus, the purpose of the present study was to determine both the total and soluble oxalate content of various types of commercially available pastas.
2. Materials and methods 2.1. Samples and sample preparation The following types of pasta products were assessed for both total and soluble oxalate: spaghetti (three different brands), lasagne (two brands), penne pasta (three brands), macaroni (three brands), egg noodles (two brands), brown rice pasta (three brands), vegetable-pasta blends (three brands), and five different types of whole wheat pastas. All pasta products were purchased from local establishments in Laramie, Wyoming. Pasta samples were boiled in water for the time periods specified on the package; boiling times ranged from 7 min (egg noodles pasta) to 20 min (one of the lasagna samples). After boiling, samples were drained in a colander for 2 min, weighed, frozen at 25 8C for approximately 24 h, and then freeze-dried (Freezemobile 6, Virtis Company, Gardiner, NY) for approximately 48 h to achieve a constant dry weight. Freezedried samples were initially ground with a mortar and pestle and then in a Pavoni coffee mill until the particles could not be further homogenized. Since the primary ingredient for the majority of pasta samples tested was semolina flour, which is obtained from
M. Liebman, J. Okombo / Journal of Food Composition and Analysis 22 (2009) 254–256
grinding Durum wheat, we also analyzed the oxalate content of a commercially available brand of semolina flour. 2.2. Total and soluble oxalate extraction Total and soluble oxalates were extracted according to a previously described method (Ross et al., 1999). Duplicate finely ground pasta samples (or semolina flour samples) ranging from 1.5 to 1.8 g were weighed into 500 mL beakers after which 50 mL of 2 M H3PO4 (for total oxalate) or 50 mL of distilled deionized water (for soluble oxalate) was added. The contents were then mixed, beakers covered with aluminum foil, and then placed in a shaking water bath at 80 8C for 30 min. After cooling and bringing the volumes up to 100 mL with distilled deionized water, the diluted extractions were centrifuged at 3000 rpm for 10 min and the supernatants were filtered through Whatman number 1 filter paper. 2.3. Oxalate analysis Oxalate from filtered pasta and semolina flour samples were measured in duplicate by using an oxalate kit obtained from Trinity Biotech (Jamestown, NY). The method is based on the oxidation of oxalate by oxalate oxidase followed by detection of H2O2 produced during the reaction (Li and Madappally, 1989). Lyophilized (control) urine samples (Trinity Biotech, Jamestown, NY) providing predetermined oxalate levels of 20–30 mg/L were analyzed with each assay to ensure good quality control. 3. Results and discussion Mean (S.D.) values for total and soluble oxalate contents of various pasta products are given in Table 1. The difference between total and soluble oxalate values presented in this table represents insoluble oxalate. Knowing the proportion of total oxalate that is
255
soluble is potentially important because of the presumed higher bioavailability of soluble as compared to insoluble oxalate (Chai and Liebman, 2004; Tang et al., 2008). The results indicated that the majority of pasta products would be considered to be foods of moderate oxalate content, as the majority of samples had total oxalate contents that ranged from 20 to 30 mg/100 g wet weight and soluble oxalate contents that ranged from 5 to 12 mg/100 g. The semolina flour samples that we tested had total and soluble oxalate contents of 66.6 3.8 and 32.6 1.6 mg/100 g, respectively. Kidney stone patients who form calcium-oxalate containing stones are advised to limit their intake of foods which contain >10 mg oxalate per serving, with total oxalate intake not to exceed 50–60 mg/ day (Chicago Dietetic Association, 2000). Assuming that a 1 cup serving of pasta weighs approximately 100 g, it is clear that consumption of these foods could make a significant contribution to an individual’s total oxalate intake and would need to be limited in those following low-oxalate diets. There were variations in the oxalate content of different types of pasta that could be clinically important. The types of pasta that were lowest in total oxalate were spaghetti products (overall mean of 14.0 mg/100 g for the three different brands) and brown rice pasta (overall mean of 12.3 mg/100 g). Among the non-vegetablepasta blends, lasagne had the highest total oxalate content (overall mean of 27.5 mg/100 g for two different brands). With respect to the vegetable-pasta blends, the two that contained combinations of tomato, beet, and spinach powders in addition to flour had an overall mean of 38.7 mg oxalate/100 g. The spinach fettuccine, which contained spinach powder and Jerusalem artichoke flour, in addition to Durum semolina flour, had an oxalate content of 91.8 mg/100 g. Since spinach is known to be a very high oxalate food, with reported values as high as 1145 mg/100 g wet weight (Chai and Liebman, 2005b), it is not surprising that the proportion of spinach powder in the vegetable-pasta blends was an important determinant of the total oxalate content of these samples.
Table 1 Oxalate content of different types of pastaa. Pasta
Brand
Oxalate content (mg/100 g wet weight) Total
Moisture content (g/100 g wet weight)
Soluble
Spaghetti
1 2 3
15.6 0.5 13.7 0.4 12.7 0.1
6.6 1.1 4.1 1.3 8.3 0.8
66.4 71.2 70.7
Penne
1 2 3
25.0 0.3 23.2 1.0 22.9 0.5
6.4 1.2 7.8 0.1 9.8 0.5
63.0 61.5 59.3
Macaroni
1 2 3
19.7 0.1 26.1 1.1 20.6 1.5
3.8 0.7 10.1 1.4 4.9 0.4
69.9 66.7 63.4
Brown rice
1 2 3
10.2 0.6 12.3 0.7 14.3 1.5
2.8 0.1 2.3 0.4 2.4 0.2
63.0 61.0 67.6
Lasagne
1 2
26.4 1.6 28.5 0.1
11.7 0.9 11.5 0.6
63.1 52.8
Egg noodles
1 2
24.4 1.6 27.3 0.1
9.2 0.8 12.6 0.3
63.8 57.6
Whole wheat varieties
1 2 3 4 5
20.6 1.9 22.0 0.1 31.3 1.7 24.5 0.1 22.1 1.6
8.4 0.8 6.3 0.4 11.1 0.8 10.7 0.7 8.1 0.8
71.4 63.1 62.6 65.2 65.2
Vegetable blend
1 2
40.6 2.3 36.8 0.5
21.5 0.6 20.9 0.6
68.0 61.0
Spinach fettuccine
1
91.8 2.4
53.8 0.7
60.7
a
Sample n = 2; wet weight refers to cooked and drained weight.
256
M. Liebman, J. Okombo / Journal of Food Composition and Analysis 22 (2009) 254–256
The five whole wheat pasta samples had oxalate contents that ranged from 20.6 to 31.3 mg/100 g. The two samples with the highest oxalate levels (24.5 and 31.3 mg/100 g, respectively) both included wheat bran among the list of ingredients. These higher oxalate values can be attributed to our previously unpublished observation that wheat bran is a high-oxalate food component that contains approximately 84 mg oxalate/100 g. The remaining whole wheat pasta samples did not have higher oxalate levels than many of the other types of pasta such as penne, macaroni, lasagne, and egg noddles. This can be explained by pointing out that semolina flour, which we found in the present study to contain 67 mg oxalate/100 g, is virtually identical in oxalate content to our previously reported value for whole wheat flour (Chai and Liebman, 2005a). The oxalate levels reported in the present study are considerably higher than those that appear in the literature from other laboratories (Kasidas and Rose, 1980; Brezinski et al., 1996), but are not surprising in light of the oxalate values previously reported for various flour products (Chai and Liebman, 2005a) as well as the currently reported value for semolina flour. It should be acknowledged that the ability of various oxalate-containing foods to increase urinary oxalate excretion depends on both oxalate content and bioavailability. Thus, it is also important for future studies to determine the oxalate bioavailability of various pasta products, particularly those that are highest in oxalate.
Acknowledgment This study was supported by a grant from The VP Foundation, Graham, North Carolina.
References Brezinski, E., Durning, A.M., Grasse, B., Fusselman, E., Ciaraldi, T., 1996. Oxalate Content of Selected Foods. San Diego Medical Center, University of California. Brinkley, L.J., Gregory, J., Pak, C.Y.C., 1990. A further study of oxalate bioavailability in foods. Journal of Urology 144, 94–96. Chai, W., Liebman, M., 2004. Assessment of oxalate absorption from almonds and black beans with and without the use of an extrinsic label. Journal of Urology 172, 953–957. Chai, W., Liebman, M., 2005a. Oxalate content of legumes, nuts, and grain-based flours. Journal of Food Composition and Analysis 18, 723–729. Chai, W., Liebman, M., 2005b. Effect of different cooking methods on vegetable oxalate content. Journal of Agricultural and Food Chemistry 53, 3027–3030. Chicago Dietetic Association, 2000. Manual of Clinical Dietetics. American Dietetics Association, Chicago, IL, p. 475. Goldfarb, S., 1988. Dietary factors in the pathogenesis and prophylaxis of calcium nephrolithiasis. Kidney International 34, 544–555. Kasidas, G.P., Rose, G.A., 1980. Oxalate content of some common foods: determination by an enzymatic method. Journal of Human Nutrition 34, 255–266. Li, M.G., Madappally, M.M., 1989. Rapid enzymatic determination of urinary oxalate. Clinical Chemistry 35, 2330–2333. Massey, L.K., Roman-Smith, H., Sutton, R.A.L., 1993. Effect of dietary oxalate and calcium on urinary oxalate and risk of formation of calcium oxalate kidney stones. Journal of the American Dietetic Association 93, 901–906. Noonan, S.C., Savage, G.P., 1999. Oxalate content of foods and its effect on humans. Asia Pacific Journal of Clinical Nutrition 8, 64–74. Robertson, W.G., Hughes, H., 1993. Importance of mild hyperoxaluria in the pathogenesis of urolithiasis—new evidence from studies in the Arabian peninsula. Scanning Microscopy 7, 391–401. Ross, A.B., Savage, G.P., Martin, R.J., Vanhanen, L., 1999. Oxalate in oca (New Zealand yam) (Oxalis tuberosa Mol.). Journal of Agricultural and Food Chemistry 47, 5019–5022. Savage, G.P., Vanhanen, L., Mason, S.M., Ross, A.B., 2000. Effect of cooking on the soluble and insoluble oxalate content of some New Zealand foods. Journal of Food Composition and Analysis 13, 201–206. Tang, M., Larson-Meyer, D.E., Liebman, M., 2008. Effect of cinnamon and turmeric on urinary oxalate excretion, plasma lipids and plasma glucose in healthy subjects. American Journal of Clinical Nutrition 87, 1262–1267. Williams, H.E., Wandzilak, T.R., 1989. Oxalate synthesis, transport and the hyperoxaluric syndromes. Journal of Urology 141, 742–747.