These findings , combined with those from similar eTRE studies , suggest that the physiologically ideal time for food consumption could be in the earlier hours of the day and in close proximity to exercise sessions , which promote alignment of the feeding-fasting cycle with the circadian rhythms of human metabolism , resulting in improvement to our cardiometabolic health .
Potential downside to muscle mass ?
Maintaining muscle mass and strength as we age is a priority , as muscle and strength trend downwards after the age of 50 by approximately 1 % and 3 % a year , respectively . It is well known that increased dietary protein intake in conjunction with resistance training halts the loss of muscle tissue and strength as we age and during periods of caloric restriction .
Several investigations indicate that dietary protein should be evenly distributed throughout the day to maximise its anabolic effect on muscle tissue . Numerous studies have shown that following consumption of a meal containing protein , serum concentrations of amino acids and muscle protein synthesis rates will be increased and remain elevated for three to five hours after the meal . Owing to the rise in muscle protein synthesis after a meal , it has been demonstrated that protein intakes spaced by approximately three to four hours throughout the day lead to more favourable changes in whole-body muscle protein synthesis , compared to less frequent ingestion . TRE alters the pattern and frequency of protein ingestion in a manner that is not consistent with these current recommendations for protein intake and muscle health . Therefore , based on these considerations , a potential concern of time-restricted eating is the potential to impair muscle mass and strength .
It has been previously noted that muscle mass contributes approximately 30 % of total body weight loss in participants who are in energy restriction . In theory , less frequent feeding occasions and prolonged fasting periods could contribute to greater muscle loss with time-restricted eating . To date , only eleven studies conducted on TRE have presented data on muscle mass . Three reported a reduction , seven showed no change and one found an increase in muscle mass ( and that study used resistance training .)
Six studies have examined the effect of time-restricted eating on muscle strength and power using handgrip , vertical jump , bench press , leg press and leg extension tests for assessing one repetition maximum and repetitions to failure at 65-70 % of 1-RM . It was found that time-restricted eating had either no effect on these performance indices or these indices improved similarly between time-restricted eating and the free eating controls .
As noted , one study found an increase in muscle mass during time-restricted eating when resistance training was performed . The investigations using strength training , now totalling four studies , have been conducted by Grant Tinsley and his colleagues . They have sought to evaluate the effects of time-restricted eating in combination with resistance training on health parameters , body composition and muscle mass . The first study , which was conducted on trained male participants , used an 8-week strength training program and a TRE pattern of an 8-hour eating period ( 12pm to 8pm ). The researchers found a significant reduction in fat mass and a preservation of muscle mass compared to the 12-hour feeding group ( 8am to 8pm ).
Similarly , Tinsley et al . ( 2019 ) reported no reduction of muscle mass or maximal strength in active females performing eight weeks of TRE ( 12pm to 8pm ) while performing progressive resistance training , compared to a control group with an eating window of approximately 13-hours .
In another investigation , Tinsley et al . ( 2017 ) examined the effects of 8-weeks of resistance training in trained men , with TRE performed only on days without strength training and the eating period being a more intense 4 hours in the day . Compared to the group with unrestricted time to eat , no significant differences were found in weight and body composition , highlighting the important role resistance training plays in preserving muscle tissue in the absence of nutrition .
In all of the other Tinsley studies , daily TRE with an eating window of approximately 8 hours was employed . The findings have demonstrated equivalent muscle mass changes in TRE and control groups when both groups consumed 1.6 to 1.9 grams per kg of body mass per day of protein and similar total energy .
Taken as a whole , the studies from Grant Tinsley and co-workers strongly indicate that time-restricted eating requires resistance training in combination with adequate energy and protein intake to prevent a reduction in muscle tissue . Tinsley has noted that although the pattern and frequency of protein ingestion is important in certain contexts , the overall daily intake of protein and resistance training must be considered as the primary factors for increasing or maintaining muscle mass .
Summary
Time-restricted eating seeks to align our eating patterns with the time of day when we are most active . Studies suggest that shifting our eating periods to earlier in the day and in proximity to our exercise sessions is a strategy better matched to our evolutionary circadian biology and can improve many markers of health . To help preserve or even build muscle mass during time-restricted eating , a daily protein intake of 1.6 to 1.9g per kilogram of body mass is recommended in combination with resistance training .
Dr Tony Boutagy , PhD Tony is a strength coach and personal trainer who has been providing training and education in the fitness industry for over two and a half decades . He holds a PhD in sports science and can be found at
tonyboutagy . com .
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