Nutritional interventions are important for reducing
obesity and related conditions. Soy is a good source of
protein and also contains
isoflavones that may affect plasma
lipids,
body weight, and
insulin action. Described here are data from a monkey breeding colony in which monkeys were initially fed a standard chow diet that is low fat with
protein derived from soy. Monkeys were then randomized to a defined diet with a fat content similar to the typical American diet (TAD) containing either
protein derived from soy (TAD soy) or
casein-
lactalbumin (TAD
casein). The colony was followed for over two years to assess
body weight, and
carbohydrate and
lipid measures in adult females (n=19) and their offspring (n=25). Serum
isoflavone concentrations were higher with TAD soy than TAD
casein, but not as high as when monkey chow was fed. Offspring consuming TAD soy had higher serum
isoflavone concentrations than adults consuming TAD soy. Female monkeys consuming TAD soy had better
glycemic control, as determined by
fructosamine concentrations, but no differences in
lipids or
body weight compared with those consuming diets with TAD
casein. Offspring born to dams consuming TAD soy had similar
body weights at birth but over a two-year period weighed significantly less, had significantly lower
triglyceride concentrations, and like adult females, had significantly lower
fructosamine concentrations compared to TAD
casein.
Glucose tolerance tests in adult females were not significantly different with diet, but offspring eating TAD soy had increased
glucose disappearance with overall lower
glucose and
insulin responses to the
glucose challenge compared with TAD
casein. Potential reasons for the additional benefits of TAD soy observed in offspring but not in adults may be related to higher serum
isoflavone concentrations in offspring, presence of the diet differences throughout more of their lifespan (including gestation), or different tissue susceptibilities in younger animals.