Chronic effects of a high protein diet on body mass, energy intake, and 24-hour subjective appetite measured under highly controlled conditions inside a metabolic chamber in older men

Rationale: A high protein (HP) diet may assist in attenuating age-related declines in FFM but may also affect appetite, known to decline with age. This study investigated the chronic effects of a HP diet on body mass, energy intake, and 24-hour subjective appetite in older men.
Methods: 33 older men (age: 67±1yrs; BMI: 25.4±0.4 kg/m2) were randomised to consume either a HP (∼1.6g/kg/day and ∼25% of energy intake (EI); n=17) or a control diet ((CON) ∼1g/kg/day and ∼15% of EI; n=16) for 12 weeks. Diets were achieved via energy-matched supplements (HP: 2x25g/day whey protein isolate; CON: 2x23.75g/day maltodextrin). Dietary intake was assessed every 6 weeks. At baseline and 12 weeks, body mass was measured and participants resided in metabolic chambers1 during which subjective appetite (hunger, satiety, fullness, and desire to eat) was measured 9 times over 24 hours via visual analogue scales (VAS).
Results: In the HP group, compliance with the WP supplements was high (96±3%), achieving a protein intake of 1.6±0.2g/kg/day (25±4% EI) at 6- and 12 weeks, which significantly differed to the CON group (1.0±0.2g/kg/day (15±2% EI), p<0.001). Total EI was similar between groups at 6 weeks (p=0.44) but increased in the CON group greater than the HP group at 12 weeks (+169±41kcal/day vs. +34±40kcal/day, p=0.03). Body mass remained stable in the HP group (0.0±0.4kg) but increased greater in the CON group (1.1±0.4kg, p=0.04). No differences in any appetite VAS outcome occurred between groups (p>0.23).
Conclusion: A HP diet (∼1.6g/kg/day and ∼25%EI) via whey protein supplementation is achievable in older men and whilst does not increase body mass or EI to the same extent as a control diet with higher carbohydrate, does not adversely affect these outcomes or subjective appetite.