Increased Dietary Protein Consumed at Breakfast Leads to an Initial and Sustained Feeling of Fullness During Energy Restriction Compared to Other Meal Times

The objective of the study was to assess whether the timing of increased dietary protein throughout the day influences the feelings of fullness during energy balance (EB) and restriction (ER). Nine men (age 48 (sem 6) years; BMI 32.7 (sem 0.7) kg/m2) randomly completed five controlled feeding trials, each consisting of 3 d of EB, followed by 3 d of ER of a 3138 kJ/d (750 kcal/d) reduction). The diet was composed of a normal amount of protein (NP) (0.8 g protein/kg per d), or an additional amount of protein (HP) (+0.6 g protein/kg per d) given at breakfast (HP-B), lunch (HP-L), dinner (HP-D) or equally divided among all meals (HP-E). Meal-related (3 h postprandial) and overall (15 h composite) feelings of fullness were assessed from thirteen-point, numbered, linear category scale questionnaires (reported as arbitrary units (au)). When comparing HP treatments, the data are presented as difference from NP. No differences in meal-related or overall fullness were observed among HP treatments during EB. During ER, the HP-B led to greater meal-related fullness (+137 (sem 44) au x 180 min) compared to HP-D ( -1 (sem 37) au x 180 min; P = 0.003), but not for HP-L (+62 (sem 53) au x 180 min; P = 0.188) or HP-E-B (+92 (sem 85) au x 180 min; P = 0.587). HP-B also led to greater overall (15 h) fullness (+404 (sem 162) au x 900 min) v. HP-L (+33 (sem 162) au x 900 min; P = 0.009) and HP-D ( -60 (sem 132) au x 900 min; P = 0.05), but not HP-E (+274 (sem 165) au x 900 min; P = 0.188). The initial and sustained feelings of fullness following protein consumption at breakfast suggests that the timing of protein intake differentially influences satiety during ER.