Somatotropic responses to soy protein alone and as part of a meal.

AB - CONTEXT: Growth hormone (GH) is an important regulator of growth and body composition. We previously showed that GH release can be promoted by oral ingestion of soyprotein, it is not known however whether these somatotropic effects of soy protein are also present when soy protein is ingested as part of a complete meal. OBJECTIVE/DESIGN: We compared effects of oral ingestion of soyprotein alone with effects of a meal containing the same amount of soyprotein on GH secretion in six healthy women (BMI=19-26kg/m2; 19-36years), in a randomized crossover design. During the complete experiment serum GH, insulin and glucose were determined every 20 minutes. RESULTS: GH responses as determined by area under the curve (AUC) and peak values were lower after ingestion of the meal, in comparison with after the soy protein consumption alone (p<0.05), and did not differ from the placebo condition. Glucose-responses and insulin-responses, both determined as area under the curve (AUC) and peak values, were higher after ingestion of the meal, compared with these after ingestion of the protein-drink or the placebo (p<0.05). CONCLUSION: The somatotropic effect of soy protein is reduced and delayed when soy protein is ingested as part of a complete meal. Dietary carbohydrates, by increasing serum levels of glucose and insulin concentration, as well as dietary fat, may have interfered with the somatotropic effects of soy protein.