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Does the feeding window matter for muscle mass?

Time-restricted feeding (TRF) may have a negative impact on muscle mass, at least in theory. This study put the question to the test by examining both TRF’s and HMB supplementation’s effects in resistance-training women.

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

Introduction

Time-restricted feeding (TRF) is an intermittent fasting strategy in which all food intake is restricted to a specific time window during the day (for example, eight hours per day). According to the vast data[1] from animal models and in vitro experiments, as well as emerging data in humans, daily fasting could have beneficial health effects, in addition to those derived from[2] weight loss. However, much of the current literature on TRF has been focused on populations with metabolic abnormalities, so studies performed on healthy, active individuals are still scarce.

One of the most frequently voiced concerns about fasting is its potentially detrimental effect on lean mass, as longer periods of low or no energy intake have a net catabolic[3] effect. As preservation of muscle mass[4], and particularly[5] strength, appears to be important for overall health, periods of fasting have not been classically recommended as part of a healthy dietary pattern. Some authors have suggested[6] that regimens which incorporate fasting, in the context of caloric restriction, have detrimental effects on lean mass. However, corresponding studies that would test this hypothesis in the context of resistance training and adequate protein intake are still limited in number. In fact, only two previous studies have compared TRF to a usual diet in resistance trained men. One[7] showed an attenuation of increases of lean mass, while the other[8] showed no differences compared to the control group, which could be explained by methodological differences (discussed later in the review).

A supplement which has previously been proposed as a means to reduce protein degradation during extended periods of fasting, and hence attenuate any loss of lean mass, is beta-hydroxy beta-methylbutyrate (HMB), a metabolite of the amino acid leucine, which has[9] anti-catabolic and anabolic properties. To date, no study has tested the effects of this compound during a TRF intervention when the latter was coupled with regular resistance exercise. In addition, the two previously mentioned studies on TRF have been performed with male participants, and there appears to be differential[10] responses to fasting between men and women. Therefore, the objective of the study under review was to determine the effects of TRF, with or without HMB supplementation, during a period of standardized resistance training on body composition, muscle performance, and selected physiological variables.

Time-restricted feeding could impact health negatively by possibly reducing lean mass. This negative side effect may be attenuated by potentially anti-catabolic supplements like HMB. However, little research has been done on this topic, and most of the existing research has only been performed in men. The study under review is designed to fill the corresponding gaps in the research by determining the effects of TRF with or without HMB supplementation in healthy women performing resistance exercise.

Who and what was studied?

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