Effects of high and normal soyprotein breakfasts on satiety and subsequent energy intake, including amino acid and 'satiety' hormone responses.

BACKGROUND: The role of dietary protein in short term satiety is of interest with respect to body weight regulation. AIM: To compare the effects of a high versus a normal soyprotein breakfast on satiety and subsequent energy intake (EI), including 'satiety' hormones and plasma amino acid responses. METHODS: Twenty-five healthy subjects (mean +/- SEM, BMI: 23.9 +/- 0.3 kg/m(2); age: 22 +/- 1 years) received a subject-specific standardized breakfast: a custard with soy as single protein type with either 10/55/35 (normal-protein) or 25/55/20 (high-protein) En% protein/carbohydrate/fat in a randomized, single-blind design. Appetite profile (Visual Analogue Scale, VAS), plasma glucose, insulin, Glucagon-like Peptide 1, ghrelin, and amino acid concentrations were determined for 4 h, determining the sensitive time point to assess EI. Since at 180 min glucose and insulin concentrations still were significantly different, in a second set of experiments subjects received an ad lib lunch at 180 min after the breakfasts; EI was assessed. RESULTS: Overall the 25 En% soy-custard was rated as being more satiating than the 10 En% soy-custard (P < 0.01) and there was a difference at 20 min after breakfast (64 +/- 5 vs. 52 +/- 5 mmVAS, P < 0.05), related to higher postprandial taurine concentrations (P < 0.05). Insulin response was increased more after the 25 En% than after the 10 En% soy-custard (AUC: 7,520 +/- 929 vs. 4,936 +/- 468 mU/l h, P < 0.001). There was no difference in EI (25 En%: 3,212 +/- 280 kJ vs. 10 En%: 3,098 +/- 286 kJ, ns). CONCLUSION: A high soyprotein breakfast is more satiating than a normal soyprotein breakfast related to elevated taurine and insulin concentrations.