Objective: This study evaluated the effects of acute and chronic consumption of higher dietary protein on energy expenditure, macronutrient use, appetite, and appetite-regulating hormones during weight loss in women.
Research methods and procedures: Thirty-eight women chronically consuming a 750 kcal/d energy-deficit diet with a protein content of 30% (higher protein-chronic diet, HP-CD, n = 21) or 18% (normal protein-chronic diet, NP-CD, n = 17) for 9 weeks were tested. On separate days, metabolic, appetite, and hormonal responses were measured over 4 hours when the women consumed a higher protein-acute meal (HP-AM) (30% of energy as protein) or a normal protein-acute meal (NP-AM) (18% of energy as protein).
Results: With chronic diet groups combined, HP-AM led to lower respiratory exchange ratio (0.829 +/- 0.005 vs. 0.843 +/- 0.008; p < 0.05), lower carbohydrate oxidation (p < 0.05), and higher fat oxidation (p < 0.05) compared with NP-AM. HP-AM also led to reduced self-reported postprandial hunger (p < 0.001) and desire to eat (p < 0.001) and lower postprandial ghrelin (252 +/- 16 vs. 274 +/- 18 ng/mL x 240 minutes, p < 0.05) compared with NP-AM. No differences in postprandial energy expenditure (PPEE) occurred between meals. When combining acute meals, respiratory exchange ratio was lower (p < 0.05) and protein oxidation (p < 0.001) was higher in the HP-CD vs. NP-CD. An acute meal-by-chronic diet interaction was observed with PPEE such that HP-AM led to greater PPEE in the HP-CD vs. NP-CD (28.7 +/- 2.7 vs. 19.9 +/- 2.7 kcal/min for 195 minutes; p < 0.05).
Conclusions: During weight loss, thermogenesis and protein use appear to be influenced by chronic protein intake, while appetite and ghrelin are more responsive to acute protein intake.