Time-Restricted Eating during a Bulking Phase Is Associated with Reduced Fat Accumulation, while Muscle and Strength Gains Are Maintained: A 12-Wk Randomized Controlled Trial.

BACKGROUND

Bulking strategies in resistance-trained individuals typically involve high meal frequency and long eating windows.

OBJECTIVES

The present study aimed to investigate whether time-restricted eating [TRE (16:8 protocol)] can affect nutrient intake, body composition, 1-repetition maximum (1RM) performance, and resting hormone levels during a bulking phase in resistance-trained individuals.

METHODS

Twenty-three healthy individuals were randomly assigned to either a TRE or a control (CON) group. All participants completed intense resistance training 3 times per week for 12 wk and were instructed to consume 300 to 500 kcal above their individualized daily energy requirements. Body composition (measured by single-frequency bioelectrical impedance analysis) and 1RM performance were assessed every 4 wk. Hormone levels were measured at baseline and after intervention, and the Hooper questionnaire for monitoring well-being was completed daily.

RESULTS

TRE consumed significantly fewer calories than prescribed [target intake: 37.50 ± 4.87; actual intake: 31.86 ± 7.52 kcal/kg body weight (BW), P = 0.001], with lower protein intake (1.60 ± 0.20; 1.44 ± 0.31 g/kg BW, P = 0.025) and lower carbohydrate intake (5.27 ± 1.19; 3.97 ± 1.29 g/kg BW, P < 0.001). Despite this, both groups showed similar increases in fat-free mass (TRE: +1.34 ± 0.78; CON: +1.38 ± 1.42 kg) and muscle mass (+1.07 ± 0.94; +1.13 ± 0.61 kg). The CON group showed significantly greater increases in BW (+2.19 ± 2.40; +3.90 ± 2.14 kg; P = 0.018) and fat mass (+2.00 ± 2.49; +4.36 ± 2.26 kg; P = 0.009). Similar increases in 1RM performance were observed for both deadlift (+26.36 ± 10.92; +26.04 ± 8.01 kg) and bench press (+12.95 ± 7.23; +11.04 ± 3.61 kg). There were no meaningful differences between the groups regarding hormone levels and questionnaire results.

CONCLUSIONS

The lower total energy intake in the TRE group was associated with smaller increases in fat mass, reflecting reduced adherence to the prescribed energy surplus within the restricted eating window. Nevertheless, the results indicate that sufficient macronutrients were consumed to support increases in muscle mass and strength comparable with those observed in the CON group. This study was registered at the German Clinical Trials Register as DRKS-ID: DRKS00038177.