Thirty-two overweight women were randomly assigned to follow either high- or normal-protein diets, with or without time-restricted eating, while completing an 8-week supervised resistance training program. Researchers measured changes in visceral and subcutaneous fat, lean mass, and appetite hormones to see if protein intake and eating windows resulted in significantly different outcomes.
Overview
- What did they test? Researchers compared four groups of overweight women: high-protein (1.6 g per kilogram of body weight per day) with time-restricted eating, normal protein (0.8 g/kg/day) with time-restricted eating, high protein without time restriction, and normal protein without time restriction. All participants followed an 8-week, 25% calorie-restricted diet and a supervised resistance training program (three sessions per week). Body composition was assessed with MRI to quantify visceral and subcutaneous fat and bioelectrical impedance to estimate fat mass and fat-free mass. Blood samples were taken to measure appetite-related hormones (leptin and ghrelin) and other metabolic markers. Strength was tested by one-repetition maximum (1RM) in the bench press and leg press, while muscular endurance was measured by the number of repetitions completed at 65% of 1RM for each lift.
- What did they find? All groups lost fat, but the high-protein time-restricted eating group saw the largest drop in subcutaneous and visceral fat while also maintaining lean mass. Normal-protein groups lost more lean tissue. Leptin levels decreased across all groups, but ghrelin levels appeared to remain stable in all groups.
- What does it mean for you? If you’re starting resistance training with the goal of losing fat without losing muscle, or supporting someone who is, combining high-protein intake with time-restricted eating might be worth experimenting with. Time-restricted eating may be a helpful tool for managing calories, but it isn’t a magic bullet. If you’re aiming to lose fat while keeping muscle, focus first on hitting protein targets and training consistently—using time-restricted eating only if it helps you stick to your plan.
What’s The Problem?
Losing fat while holding on to muscle is notoriously difficult. Time-restricted eating (TRE) has grown popular as a weight-loss strategy, with research showing it can reduce body weight, blood pressure, and improve glucose control—even without changes in total calorie intake 1 2. But a common drawback of calorie restriction and TRE is the loss of lean mass, which can compromise metabolism and increase the risk of fat regain after dieting 3 4. Preserving muscle during weight loss is critical, particularly for individuals beginning resistance training. High-protein diets are a proven way to maintain or even increase muscle mass while dieting, especially when combined with strength training 5 6. Yet, few studies have directly tested whether combining TRE with a high-protein diet and resistance training can maximize fat loss while protecting lean mass. This trial was designed to help fill that gap in the literature.
Purpose
The researchers aimed to investigate the potential synergistic effects of time-restricted eating (TRE) combined with high-protein intake compared with either intervention alone in overweight women starting resistance training and following a calorie-restricted diet.
Hypothesis
The researchers hypothesized that: (a) TRE particularly when combined with a high-protein, calorie-restricted diet, would significantly reduce visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) compared with other dietary interventions during resistance training (RT). (b) Additionally, TRE with high-protein intake would result in favorable changes in appetite-regulating hormones (leptin and ghrelin). (c) This approach would better preserve or enhance fat-free mass (FFM) during the initial phase of training.
