Satiating Effect of High Protein Diets on Resistance-Trained Subjects in Energy Deficit

Abstract

Short-term energy deficit strategies are practiced by weight class and physique athletes, often involving high protein intakes to maximize satiety and maintain lean mass despite a paucity of research. This study compared the satiating effect of two protein diets on resistance-trained individuals during short-term energy deficit. Following ethical approval, 16 participants (age: 28 ± 2 years; height: 1.72 ± 0.03 m; body-mass: 88.83 ± 5.54 kg; body-fat: 21.85 ± 1.82%) were randomly assigned to 7-days moderate (PRO_MOD: 1.8 g·kg^-1·d^-1) or high protein (PRO_HIGH: 2.9 g·kg^-1·d^-1) matched calorie-deficit diets in a cross-over design. Daily satiety responses were recorded throughout interventions. Pre-post diet, plasma ghrelin and peptide tyrosine tyrosine (PYY), and satiety ratings were assessed in response to a protein-rich meal. Only perceived satisfaction was significantly greater following PRO_HIGH (67.29 ± 4.28 v 58.96 ± 4.51 mm, p = 0.04). Perceived cravings increased following PRO_MOD only (46.25 ± 4.96 to 57.60 ± 4.41 mm, p = 0.01). Absolute ghrelin concentration significantly reduced post-meal following PRO_MOD (972.8 ± 130.4 to 613.6 ± 114.3 pg·mL^-1; p = 0.003), remaining lower than PRO_HIGH at 2 h (-0.40 ± 0.06 v -0.26 ± 0.06 pg·mL^-1 normalized relative change; p = 0.015). Absolute PYY concentration increased to a similar extent post-meal (PRO_MOD: 84.9 ± 8.9 to 147.1 ± 11.9 pg·mL^-1, PRO_HIGH: 100.6 ± 9.5 to 143.3 ± 12.0 pg·mL^-1; p < 0.001), but expressed as relative change difference was significantly greater for PRO_MOD at 2 h (+0.39 ± 0.20 pg·mL^-1 v -0.28 ± 0.12 pg·mL^-1; p = 0.001). Perceived hunger, fullness and satisfaction post-meal were comparable between diets (p > 0.05). However, desire to eat remained significantly blunted for PRO_MOD (p = 0.048). PRO_HIGH does not confer additional satiating benefits in resistance-trained individuals during short-term energy deficit. Ghrelin and PYY responses to a test-meal support the contention that satiety was maintained following PRO_MOD, although athletes experiencing negative symptoms (i.e., cravings) may benefit from protein-rich meals as opposed to over-consumption of protein.

Keywords: dietary protein; ghrelin; peptide YY; resistance training; satiety.

Figure 1

Plasma ghrelin concentrations following test-meal (pg·mL⁻¹; mean ± SE): (A) individual values expressed as normalised relative change to baseline levels; (B) mean values expressed as normalised relative change to baseline levels; (C) mean relative difference change (taking into consideration pre-intervention results). PRO_MOD PRO_HIGH denote moderate and high protein conditions. Dashed line provides reference point to pre-meal normalisation. * denotes significant difference overall to PRO_MOD at corresponding time-point (p = 0.015).

Figure 2

Plasma peptide YY concentrations following test-meal (pg·mL⁻¹; mean ± SE): (A) individual values expressed as normalised relative change to baseline levels; (B) mean values expressed as normalised relative change to baseline levels; (C) mean relative difference change (taking into consideration pre-intervention results). PRO_MOD and PRO_HIGH denote moderate and high protein conditions. Dashed line provides reference point to pre-meal normalisation. * denotes significant difference between dietary conditions at each time-point (p ≤ 0.018).

Figure 3

Questionnaire responses in relation to test meal under laboratory conditions. Data expressed as relative change (post diet, normalised) for both moderate (PRO_MOD) and high (PRO_HIGH) protein conditions (mean ± SE). (A) Perception of hunger; (B) Perception of fullness; (C) Perception of satisfaction; (D) Perception of desire to eat. Responses in relation to pre-meal (−30 min) time-point. 0 min denotes immediate completion of test meal. Dashed line provides reference point to pre-meal perceived state. ^* denotes significant difference compared to pre-meal time-point (p ≤ 0.05) within both dietary conditions. ^a denotes significant difference compared to pre-meal time-point for PRO_MOD only (p ≤ 0.048). No differences reported between dietary conditions.

Figure 4

Questionnaire responses in relation to test meal under laboratory conditions. Data expressed as relative difference change (baseline to post diet) for both moderate (PRO_MOD) and high (PRO_HIGH) protein conditions (mean ± SE). (A) Perception of hunger; (B) Perception of fullness; (C) Perception of satisfaction; (D) Perception of desire to eat. Responses in relation to pre-meal (−30 min) time-point. 0 min denotes immediate completion of test meal. Dashed line provides reference point to pre-meal perceived state. ^a denotes difference to pre-meal time-point within PRO_HIGH only (p = 0.028). No differences between dietary conditions observed.