Soy Protein in Weight Management

Soy protein may best be recognized for its cardiovascular heart health effects. However, it has numerous other benefits in health and wellness and, increasingly, for weight management.

In a presentation at Prepared Foods’ 2008 R&D Applications Seminar-Chicago, Elaine Krul, Ph.D., science fellow and lead, molecular nutrition, Solae LLC, indicated that soy protein is a high-quality protein, delivering essential amino acids to the body. The Protein Digestibility Corrected Amino Acid Score (PDCAAS), a method of evaluating the protein quality based on the amino acid requirements of humans, is based on the amino acid requirements (adjusted for digestibility) of a 2-5-year old child (considered the most nutritionally-demanding age group). Soy protein possesses a PDCAAS percentage of 100%, which is equivalent to egg white, whey, casein and milk¹.

High-quality proteins, such as soy, may aid in weight management through a number of mechanisms, as demonstrated in the chart titled, “Potential Mechanisms for Weight Loss on Higher Protein Diets.” A 2006 randomized, crossover study in males with normal and high BMI (body mass index) reported a significant 10% lower energy intake, after consuming three high-protein liquid preloads containing different protein sources (including soy protein). Significant postprandial suppression of ghrelin and elevations in GLP-1 and cholecystokinin were noted following 50g of whey, soy or gluten, relative to a glucose control. Changes in these metabolic para¬meters may contribute to higher satiety noted after protein consumption². Further, in a single-blind crossover study, soy protein hydrolysate induced higher DIT (dietary-induced thermogenesis) than a carbohydrate load in healthy, non-obese men³.

 Some 83 overweight and obese subjects receiving instructions to follow a lifestyle education regimen (hypo-caloric diet) for six months experienced a significant decrease in BMI. However, feeding a high soy protein-enriched diet was associated with a greater decrease in fat mass in comparison with subjects who received the lifestyle education regimen⁴.

The supplementation of 20g soy protein with 96mg isoflavones was associated with a decrease  in subcutaneous and total abdominal fat, when compared to supplementation with an isocaloric casein placebo in 15 post-menopausal women without diabetes in a randomized, double-blind, placebo-controlled, 3-month trial. Researchers are conducting studies to understand how soy protein may exert such effects on adipose tissue, but further research is needed. For instance, one research group noted a restoration in activated AMP-kinase in adipose tissue after 13 weeks in mice fed a high-fat (HF) diet with the black soy peptides (BSP) vs. mice on a HF-diet alone. These mice also gained less body weight than those fed a HF-diet, without BSP, concurrent with inhibition of total food intake in a dose-dependent manner⁵.

Additionally, soy protein has some unique health benefits that are important in the context of weight management. Soy protein consumption is associated with reductions in plasma cholesterol, and a coronary heart disease risk reduction health claim by the FDA was approved in 1999 for soy protein. Recently, some attention has focused on the ability of soy protein to lower triglycerides and to reduce blood pressure. Also, increased protein (including soy protein) in food formulations can reduce the glycemic index of foods, leading to an improvement in gluco-regulatory mechanisms.

Foods naturally rich in soy protein are low in saturated fat and refined carbohydrates--properties inherently beneficial in diets to manage weight. Data presented support soy protein as a high-quality protein which offers significant nutritional benefits in weight-loss regimens. Krul concluded that, although more work is needed, emerging research promises to identify mechanisms for soy protein’s benefits in weight management regimens, allowing industry to optimize soy protein processing and healthy food delivery forms of this important protein. NS

“The Role of Soy Protein in Weight Management,” Elaine S. Krul, Ph.D., science fellow and lead, molecular nutrition, Solae LLC, ekrul@solae.com, www.solae.com

References:
¹ Castellanos VH, et al. 2006. Nutr Clinical Practice21:485-504.
² Bowen J, et al. 2006. J Clin Endo Metab 91:2913-2919.
³ Claessens M, et al. 2007. Metab Clin Exp 56:1051-1059.
⁴ Deibert P, et al. 2004. Intl J Obes 28: 1349-1352.
⁵ Jang E-H, et al. 2008. Intl J Obes 32: 1161-1170.