(PTFS07-05-23) Appetite and Food Intake Responses to Protein in Older Adults With Different Physical Activity Levels

Objectives: Older adults are recommended to increase their protein intake and physical activity to maintain their muscle mass. Physical activity is also recommended to enhance appetite in older adults, as it has been shown to help regulate appetite in younger adults. However, protein is considered the most satiating macronutrient and therefore this recommendation may result in a reduction in total energy intakes. The objective of this study was to investigate the impact of physical activity and protein on food intake, perceived appetite, and gastric emptying in older adults.

Methods: Nineteen active (70.8 (SD 4.5) years; body mass index (BMI) 23.2 (SD 3) kg/m²) and 19 less active (70.4 (SD 2.6) years; BMI 25.2 (SD 2.4) kg/m²) older adults completed a single-blind, randomised, crossover trial involving two test days. Participants received a standard breakfast, followed three hours later by an isovolumetric (250 ml) and isocaloric (~300 kcal) high protein (57% protein/energy) or low protein (17% protein/energy) preload milkshake matched for sensory properties. Three hours after the preload, participants were offered an ad libitum meal. Food intake was assessed by weight, perceived appetite was assessed using 100 mm visual analogue scales and gastric emptying was measured via the ¹³C-octanoic acid breath test.  

Results: Subsequent energy intake was suppressed by the higher protein preload in the active and less active groups combined (F(1,36) = 4.39, p = 0.043, n_p² = 0.11), but there was no effect of physical activity. Protein had no effect on appetite scores (p > 0.05). Gastric emptying half time (123.4% or other quantification of the difference) was longer following the high protein milkshake than the low protein milkshake (F(1,35) = 30.0, p < 0.001, n_p² = 0.46). The active group had a lower perceived appetite (from hunger, fullness and prospective consumption ratings) (p < 0.05), but faster gastric emptying compared to the less active group (F(1,35) = 8.0, p = 0.008, n_p² = 0.19).

Conclusions: In conclusion, higher protein intake suppresses subsequent food intake and slows gastric emptying in older adults, regardless of physical activity level. Although being physically active accelerates gastric emptying in older adults, it has no compensatory effect on the decreased food intake caused by protein intake.

Funding Sources: Republic of Turkey Ministry of National Education