Acute effects of breakfasts containing -lactalbumin, or gelatin with or without added tryptophan, on hunger, satiety hormones and amino acid profiles

Abstract

Proteins are the most satiating macronutrients. Tryptophan (TRP) may contribute to the satiating effect, as it serves as a precursor for the anorexigenic neurotransmitter serotonin. To address the role of TRP in the satiating properties of dietary protein, we compared three different breakfasts, containing either α-lactalbumin (high in TRP), gelatin (low in TRP) or gelatin with added TRP (gelatin+TRP, high in TRP), on appetite. Twenty-four subjects (2229kg/m2; aged 1937 years) received a subject-specific breakfast at t = 0 with 10, 55 and 35% energy from protein, carbohydrate and fat repectively in a randomised, single-blind design. Hunger, glucagon-like peptide (GLP)-1, ghrelin, amino acid concentrations and energy intake during a subsequent lunch were determined. Suppression of hunger was stronger 240min after the breakfast with -α-lactalbumin compared with gelatin and gelatin+TRP. Total plasma amino acid concentrations were lower with -α-lactalbumin compared with gelatin with or without TRP (from t = 180240min). TRP concentrations were higher after -α-lactalbumin than after gelatin with or without TRP from t = 0100min, whereas from t = 100240min, TRP concentrations were lower after gelatin than after -α-lactalbumin and gelatin+TRP. The plasma ratio of TRP to other large neutral amino acids (LNAA) was, only at t = 100min, lower after gelatin+TRP than after the other breakfasts. Plasma amino acid responses, TRP concentrations and TRP:LNAA ratios were not correlated with hunger. GLP-1 and ghrelin concentrations were similar for all diets. Energy intake during a subsequent lunch was similar for all diets. Summarised, an -α-lactalbumin breakfast suppresses hunger more than a gelatin or gelatin+TRP breakfast. This cannot be explained by (possible) differences found in TRP concentrations and TRP:LNAA ratios in the breakfasts and in plasma, as well as in ciruclating total amino acids, GLP-1 and ghrelin.