This study explores how protein intake influences appetite regulation in resistance-trained individuals under a short-term caloric restriction and whether increasing intake improves satiety and reduces hunger.
Overview
- What did they test? The researchers investigated the impact of two high-protein diets on appetite and satiety in resistance-trained individuals undergoing seven days of 20% caloric restriction.
- What did they find? A higher protein intake (2.9 g/kg/day) showed similar effects on appetite and satiety compared to a moderate protein intake (1.8 g/kg/day).
- What does it mean for you? Adopting a high-protein diet may aid in controlling hunger and maintaining muscle mass during periods of reduced caloric intake.
What’s the problem?
Appetite responses can make weight loss difficult, often increasing as body fat decreases. In fact, research shows that for every kilogram of weight lost, appetite increases by about 100 kcal per day, creating a compensatory drive to eat more that can add up quickly over time 1. High-protein diets are widely used in weight loss programs for their positive effects on appetite regulation and gastrointestinal hormones. For instance, a systematic review found that high-protein diets increase satiety and fullness in individuals with overweight and obesity 2. However, a potential concern with a consistent high-protein diet is appetite habituation, which may reduce appetite-suppressing effects and limit long-term benefits of high protein intake during a diet 3.
One method to measure appetite and satiety is individual perception (i.e., subjective feelings) which is generally measured by questionnaire. This approach involves asking participants to rate their feelings of hunger, fullness, satisfaction, and desire to eat at various time points, often using a visual analogue scale (VAS) to quantify responses. These self-reported measures provide insights into the immediate and sustained effects of dietary interventions on appetite, allowing scientists to assess how different nutrient compositions, meal timings, and caloric intakes impact perceived hunger and satiety after eating. For example, Apolzan et al. (2007) found that consuming protein at 125% (1.0 g/kg/day) of the recommended dietary allowance (RDA) reduced hunger and desire to eat compared the RDA (0.8 g/kg/day) under isocaloric conditions in both younger and older men over 18 days 4.
Another method to measure appetite and satiety are hormones, which are objective. Peptide YY (PYY) and ghrelin are two hormones that regulate appetite: PYY promotes satiety and reduces food intake after meals, while ghrelin stimulates hunger by signaling the brain to drive food consumption. A meta-analysis of randomized controlled trials found that under isocaloric conditions, protein intake acutely reduced hunger, desire to eat, and prospective food consumption, while increasing fullness and satiety 5. Furthermore, the authors found that protein decreased ghrelin but caused no changes in PYY. Interestingly, the effects were dose-dependent, with significant hormonal changes occurring only after eating 35 grams or more protein 5.
Some research suggests that protein needs for energy-restricted resistance-trained athletes are increased with severity of caloric restriction and leanness 6. Indeed, a recent study on bodybuilders using an isotope-tracing method found that the estimated average requirement of protein was between 1.7 and 2.2 g/kg/day 7. These studies primarily focus on lean mass; however, since appetite increases with weight loss, it would be valuable to understand if protein intake also improves appetite.
The current study under review contributes to existing research as one of the first to examine the effects of two high-protein diets during an energy deficit in resistance-trained individuals already having an above-average protein intake (1.8 g/kg/day), focusing on the hormonal and subjective response.
Purpose
This study compared the effects of two protein diets (PROhigh: 2.9 g/kg/day vs PROmod: 1.8 g/kg/day) on subjective appetite response and hunger hormones in resistance-trained individuals who were in a 20% energy deficit for one week and a 3-day free-eating period afterward.
Hypothesis
The authors hypothesized that a protein intake of 2.9 g/kg/day would not impact satiety levels more than an intake of 1.8 g/kg/day but that it might reduce training motivation.
