Growth hormone responses to ingestion of soyprotein with or without fat and/or carbohydrate in humans

SummaryBackground & aimGrowth hormone (GH) is an important regulator of growth and body composition. It has been shown that GH release can be promoted by administration of various amino acids, such as arginine and lysine, that are present in soyprotein. Soyprotein ingestion increases GH secretion more than the ingestion of a combination of arginine and lysine. The GH promoting effect of soyprotein however is not present when soyprotein is ingested combined with carbohydrate and fat. The aim of this study is to investigate whether carbohydrate or fat eliminates the GH promoting effect of soyprotein.MethodsWe compared ingestion of soyprotein plus carbohydrate (soy + carbohydrate) or soyprotein plus fat (soy + fat) with ingestion of soyprotein alone (soy), soyprotein plus carbohydrate plus fat (soy + carbohydrate + fat) and a placebo. The study was performed in eight healthy women (age: 21 ± 1.5 years, BMI: 22 ± 1.8 kg/m2) in a randomized, single blind, placebo-controlled crossover design. GH, insulin, glucose and AA concentrations were measured during 5 h.ResultsIngestion of soy + carbohydrate or soy + fat stimulated GH responses to the same extent than soy (IAUC; 374 ± 50 min μg/L, 400 ± 57 μg/l.5 h, 403 ± 73 μg/l.5 h respectively), but more than after the ingestion of soy + carbohydrate + fat or placebo (IAUC; 226 ± 43 μg/l.5 h, 84 ± 52 μg/l.5 h respectively) (p < 0.05). Insulin responses were higher after ingestion of soy + carbohydrate or soy + carbohydrate + fat, than after soy + fat or soy (p < 0.05). Compared with placebo, all conditions showed higher insulin concentrations (p < 0.05). Glucose responses were higher after ingestion of soy + carbohydrate than after the other conditions (p < 0.05). Peak plasma arginine concentrations were higher after the ingestion of soy compared with soy + carbohydrate + fat (p < 0.05).ConclusionThe GH promoting activity of soyprotein depends on the macronutrient composition, in that, fat and carbohydrate should not be present at the same time. Serum arginine concentrations may be involved in the somatotropic activity of protein. Glucose and insulin responses however are not involved.