Soy & Obesity

Approximately 30 percent of U.S. adults age 20 and older are obese (body mass index [BMI] ≥ 30 kg/m^-2) and 16 percent of children ages 6-19 years are overweight (BMI ≥95^th percentile of the gender-specific BMI for age chart).¹

Obesity is recognized as a major risk factor for many health issues including diabetes. In fact, an increase in body weight of approximately 2.2 pounds (1 kg) has been shown to increase risk for developing diabetes by 4.5 percent whereas a 5- 10 percent decrease in body weight improves diabetes control.² Obesity is closely correlated with diabetes. In fact, obesity-induced diabetes is now termed diabesity, formerly known as metabolic syndrome.

Soy & Weight Loss

In a comprehensive review, Bhathena and Velasquez concluded that, in comparison to casein (milk protein), soy protein promotes less gain in body fat. In particular, the soy protein fraction beta-conglycinin has been shown to reduce weight gain in animals^{3, 4} although results from a recent study in humans were mixed.⁵

While there may be relatively little clinical evidence that soy protein increases energy expenditure⁶ or satiety^{6, 7} compared to other proteins, there is no doubt that soy protein can be an effective component of meal replacements, which are known to successfully promote weight loss.^{8, 9}

Allison et al. found in a 12-week prospective controlled clinical trial in which obese subjects were randomized to either the soy-based meal replacement formula treatment group or control group, that the treatment group lost significantly more weight (7.00 vs. 2.90 kg) and had a greater decrease in total cholesterol levels.¹⁰

More recently Anderson et al. found that in obese women, weight loss associated with consumption of soy protein-based meal replacements was as great as that associated with casein-based meal replacements.¹¹ As noted by Allison et al., the reduction in total cholesterol and low-density lipoprotein cholesterol was greater in response to the soy diet.

In a recent comprehensive analysis in which the effectiveness of different nutritional approaches on weight loss in obese individuals were compared, Anderson et al. found that low-energy diets containing soy protein were more efficacious than meal replacements and energy-restricted diets alone, and that soy diets may promote more rapid weight loss over the first 8 weeks than other interventions.¹² These conclusions should be considered speculative, however, since many of the studies upon which this finding was based were not rigorously controlled.

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Soy Protein, Higher-Protein Diets & Weight Loss

It appears that higher-protein diets are advantageous for weight loss.¹³ In a recent editorial in the American Journal of Clinical Nutrition, Arne Astrup from the Royal Veterinary & Agricultural University, Copenhagen, Denmark, suggested that it may be time to begin recommending that obese people consume diets that are 20-30 percent protein rather than the 10-20 percent currently consumed.¹⁴ This editorial was written in response to research showing that raising the protein content of the diet resulted in a spontaneous reduction in caloric intake.¹⁵

If in fact Americans adopt higher-protein diets, there will clearly be a need to identify nutritionally desirable sources of protein. Of the 65 grams currently consumed on average by adult women, 22, 14, 12 and 3 grams come from beef, poultry and pork; dairy; grains; and eggs, respectively.¹⁶

Even if dairy consumption increased an additional 10 grams so that total dairy protein intake was 24 grams/day – the amount found in three servings of dairy milk – an additional 20 grams of protein would still be required if the overall protein intake was to double. Currently, Americans consume <1 grams protein from legumes.¹⁶ Thus, legumes with high-quality protein,¹⁷ such as soy beans, are a logical choice for meeting increased protein needs.

For more information about including low-fat soy foods in a weight loss program, see the Appetite Appeal section of this site.

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References

1. Baskin ML, Ard J, Franklin F, Allison DB. Prevalence of obesity in the United States. Obes Rev 2005;6:5-7.
2. Mobley CC. Lifestyle interventions for "diabesity": the state of the science. Compend Contin Educ Dent 2004;25:207-208, 211-202, 214-208; quiz 220.
3. Nishi T, Hara H, Tomita F. Soy bean beta-conglycinin peptone suppresses food intake and gastric emptying by increasing plasma cholecystokinin levels in rats. J Nutr 2003;133:352-357.
4. Nishi T, Hara H, Hira T, Tomita F. Dietary protein peptic hydrolysates stimulate cholecystokinin release via direct sensing by rat intestinal mucosal cells. Exp Biol Med (Maywood) 2001;226:1031-1036.
5. Baba T, Ueda A, Kohno M, Fukui K, Miyazaki C, Hirotsuka M, Ishinaga M. Effects of soy bean beta-conglycinin on body fat ratio and serum lipid levels in healthy volunteers of female university students. J Nutr Sci Vitaminol (Tokyo) 2004;50:26-31.
6. Mikkelsen PB, Toubro S, Astrup A. Effect of fat-reduced diets on 24-h energy expenditure: comparisons between animal protein, vegetable protein, and carbohydrate. Am J Clin Nutr 2000;72:1135-1141.
7. Anderson GH, Tecimer SN, Shah D, Zafar TA. Protein source, quantity, and time of consumption determine the effect of proteins on short-term food intake in young men. J Nutr 2004;134:3011-3015.
8. Ashley JM, St Jeor ST, Perumean-Chaney S, Schrage J, Bovee V. Meal replacements in weight intervention. Obes Res 2001;9 Suppl 4:312S-320S.
9. Heymsfield SB, van Mierlo CA, van der Knaap HC, Heo M, Frier HI. Weight management using a meal replacement strategy: meta and pooling analysis from six studies. Int J Obes Relat Metab Disord 2003;27:537-549.
10. Allison DB, Gadbury G, Schwartz LG, Murugesan R, Kraker JL, Heshka S, Fontaine KR, Heymsfield SB. A novel soy-based meal replacement formula for weight loss among obese individuals: a randomized controlled clinical trial. Eur J Clin Nutr 2003;57:514-522.
11. Anderson JD, Fuller J, Konz E, Tabor A. 16-week randomized controlled trial of soy vs. casein meal replacements for weight management of obese women (abstract). Sixth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease (November; Chicago, IL) 2005.
12. Anderson JW, Luan J, Hoie LH. Structured weight-loss programs: meta-analysis of weight loss at 24 weeks and assessment of effects of intervention intensity. Adv Ther 2004;21:61-75.
13. Halton TL, Hu FB. The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. J Am Coll Nutr 2004;23:373-385.
14. Astrup A. The satiating power of protein - a key to obesity prevention? Am J Clin Nutr 2005;82:1-2.
15. Weigle DS, Breen PA, Matthys CC, Callahan HS, Meeuws KE, Burden VR, Purnell JQ. A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. Am J Clin Nutr 2005;82:41-48.
16. Smit E, Nieto FJ, Crespo CJ, Mitchell P. Estimates of animal and plant protein intake in US adults: results from the Third National Health and Nutrition Examination Survey, 1988-1991. J Am Diet Assoc 1999;99:813-820.
17. Rand WM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. Am J Clin Nutr 2003;77:109-127.