Time-restricted feeding plus resistance training in active females: a randomized trial

Abstract

Background: A very limited amount of research has examined intermittent fasting (IF) programs, such as time-restricted feeding (TRF), in active populations.

Objective: Our objective was to examine the effects of TRF, with or without β-hydroxy β-methylbutyrate (HMB) supplementation, during resistance training (RT).

Methods: This study employed a randomized, placebo-controlled, reduced factorial design and was double-blind with respect to supplementation in TRF groups. Resistance-trained females were randomly assigned to a control diet (CD), TRF, or TRF plus 3 g/d HMB (TRFHMB). TRF groups consumed all calories between 1200 h and 2000 h, whereas the CD group ate regularly from breakfast until the end of the day. All groups completed 8 wk of supervised RT and consumed supplemental whey protein. Body composition, muscular performance, dietary intake, physical activity, and physiological variables were assessed. Data were analyzed prior to unblinding using mixed models and both intention-to-treat (ITT) and per protocol (PP) frameworks.

Results: Forty participants were included in ITT, and 24 were included in PP. Energy and protein intake (1.6 g/kg/d) did not differ between groups despite different feeding durations (TRF and TRFHMB: ∼7.5 h/d; CD: ∼13 h/d). Comparable fat-free mass (FFM) accretion (+2% to 3% relative to baseline) and skeletal muscle hypertrophy occurred in all groups. Differential effects on fat mass (CD: +2%; TRF: -2% to -4%; TRFHMB: -4% to -7%) were statistically significant in the PP analysis, but not ITT. Muscular performance improved without differences between groups. No changes in physiological variables occurred in any group, and minimal side effects were reported.

Conclusions: IF, in the form of TRF, did not attenuate RT adaptations in resistance-trained females. Similar FFM accretion, skeletal muscle hypertrophy, and muscular performance improvements can be achieved with dramatically different feeding programs that contain similar energy and protein content during RT. Supplemental HMB during fasting periods of TRF did not definitively improve outcomes. This study was prospectively registered at clinicaltrials.gov as NCT03404271.

Keywords: body composition; energy restriction; fat loss; intermittent energy restriction; intermittent fasting; muscle mass; muscular strength; protein; resistance exercise; weight training.

FIGURE 1

Study timeline and assessments. RT, resistance training.

FIGURE 2

CONSORT flow chart. BF%, body fat percentage; CD, control diet; ITT, intention-to-treat; PP, per protocol; TRF, time-restricted feeding; TRF_HMB, time-restricted feeding plus β-hydroxy β-methylbutyrate supplementation.

FIGURE 3

Body composition changes. Results from intention-to-treat analysis are displayed [n = 40 (CD: n = 14; TRF: n = 13; TRF_HMB: n = 13)], and data from per protocol analysis are displayed in the online supporting material. Percent changes (mean ± SE) displayed as differences between W0 and W8 values relative to W0 values for each variable. Total body composition was estimated using a 4-component model, and muscle thickness was assessed via ultrasonography. Asterisks with brackets indicate significant changes in all groups (i.e., time main effects), with nonsignificant differences between groups, based on mixed model analysis and follow-up tests. BF%, body fat percentage; BM, body mass; CD, control diet; FM, fat mass; FFM, fat-free mass; MT_EF, ultrasound muscle thickness of elbow flexors; MT_KE, ultrasound muscle thickness of knee extensors; TRF, time-restricted feeding; TRF_HMB, time-restricted feeding plus β-hydroxy β-methylbutyrate supplementation.

FIGURE 4

Muscular performance changes. Results from intention-to-treat analysis are displayed [n = 40 (CD: n = 14; TRF: n = 13; TRF_HMB: n = 13)], and data from per protocol analysis are displayed in the online supporting material. Percent changes (mean + SE) displayed as differences between W0 and W8 values relative to W0 values for each variable. Asterisks with brackets indicate significant changes in all groups (i.e., time main effects), with nonsignificant differences between groups, based on mixed model analysis and follow-up tests. Muscular strength and endurance were evaluated on the hip sled (leg press) and bench press exercises, peak forces were obtained from isokinetic squat testing, rate of force development was obtained from isometric squat testing, and jump height was calculated using force platforms. 120°, 120° knee angle for isometric squat testing; 150°, 150° knee angle for isometric squat testing; 1RM_BP, 1-repetition maximum on bench press; 1RM_LP, 1-repetition maximum on leg press; CD, control diet; JH, jump height; PF_CON, peak concentric force on mechanized squat; PF_ECC, peak eccentric force on mechanized squat; RFD, rate of force development (durations over which RFD values were calculated are shown in subscripts); RTF_BP, repetitions to failure on bench press; RTF_LP, repetitions to failure on leg press; TRF, time-restricted feeding; TRF_HMB, time-restricted feeding plus β-hydroxy β-methylbutyrate supplementation.