The thermogenic and metabolic effects of protein hydrolysate with or without a carbohydrate load in healthy male subjects

High-protein diets are beneficial in weight maintenance because of their satiating and thermogenic effects. These effects may be partly mediated by the hormonal effects of proteins. This study investigated the effect of soy protein hydrolysate (SPH) with and without a carbohydrate pre- and afterload on energy metabolism and hormonal secretion in 8 healthy nonobese subjects. In an additional trial, pea protein hydrolysate was compared to SPH, both with a carbohydrate afterload. The study had a single-blind crossover design. In all cases, 0.4g protein and/or carbohydrate per kilogram of body weight was tested. Diet-induced thermogenesis (DIT) was measured by ventilated hood measurements, and postprandial blood samples were drawn over 3 hours. Soy protein hydrolysate consumption induced a higher DIT than a carbohydrate (CHO) load. Both conditions induced similar insulin responses. Soy protein hydrolysate induced a glucagon, but no glucose, response; whereas CHO induced a glucose, but no glucagon, response. Soy protein hydrolysate with a CHO pre- or afterload induced similar DIT and insulin responses. No glucose response was found when SPH preceded the CHO load. Total glucagon responses were similar with CHO as pre- and afterload, but time courses were different. Pea protein hydrolysate with a CHO afterload induced both higher insulin and glucagon responses (area under the curve) than SPH with CHO afterload, but DIT was similar in both conditions. In conclusion, this study shows that the larger DIT after protein than after CHO may be related to the glucagon response that is induced by protein but not by CHO; that the protein-induced DIT and glucagon response are not influenced by a CHO pre- or afterload; and that protein ingestion can fully prevent the plasma glucose increase associated with CHO when CHOs are ingested after proteins.