Slimming with soy

Obesity is an important risk factor for diabetes, cardiovascular diseases, high blood pressure and other conditions which are referred to as the metabolic syndrome. The rapid increase in obesity can only be stopped by a dramatic change in lifestyle factors, including more exercise and improved nutrition.

Study results

Studies with animals demonstrate that soy protein or isoflavones may help to prevent obesity and also diabetes. They indicate that consumption of soy protein reduces body weight, fat mass, cholesterol and triglycerides [1]. Already in 1996 Japanese researchers found that soy protein may be useful for the reduction of obesity [2]. When fatty rats were fed soy protein instead of casein they reduced weight after 3 weeks. Humans studies show beneficial effects of soy protein on cholesterol and tri-glicerides, but the effect on weight loss is less convincing. Anderson found that replacement of milk protein by soy protein in obese women resulted in more weight loss, but the results were not statistically significant [3]. Most of these clinical studies only involved few subjects and were limited in time. More long-term studies involving large numbers of obese subjects are required to confirm the role of soy in controlling obesity.

Soy protein and satiety

But why is soy protein often used in supplements for weight loss? It is well known that ingestion of protein suppresses appetite. For example, Herbalife uses soy protein as main ingredients in their popular shakes and bars. There is a lot of debate over which protein (soy protein, casein protein or whey protein) is the best for losing weight. The jury is still out on this.

References

[1] Role of dietary soy protein in obesity. Int J Med Sci. 2007 Feb 26;4(2):72-82.
[2] Soybean protein suppresses hepatic lipogenic enzyme gene expression in Wistar fatty rats. J Nutr. 1996 Feb;126(2):380-8.
[3] Weight loss and lipid changes with low-energy diets: comparator study of milk-based versus soy-based liquid meal replacement interventions. J Am Coll Nutr. 2005 Jun;24(3):210-6.