Time-restricted feeding (AKA “intermittent fasting”) involves eating all of the day’s calories within a fixed 4-8 hour time window. Plenty of people enjoy this feeding strategy because it either suits their daily schedule or helps them avoid overeating. However, people often wonder if the restricted feeding window limits opportunities to stimulate protein synthesis throughout the day, thereby limiting muscle and strength gains.
A recent study evaluated the effects of time-restricted feeding versus a normal feeding window in 26 men. Throughout the 4-week trial, they completed 3 full-body resistance training sessions per week and maintained a daily protein intake of around 1.8g/kg of body mass. Both diets included a 25% calorie deficit to promote fat loss. Both diet groups had statistically significant improvements in 1RM and reps to fatigue for the leg press and bench press, along with improvements in vertical jump performance. Similarly, both groups experienced significant weight loss and fat loss, while increasing biceps and vastus lateralis cross-sectional area (muscle size).
There are now a few studies indicating that time-restricted feeding does not negatively impact strength or hypertrophy outcomes over the course of a 4-8 week training program. While one study suggested that gains in lean mass were somewhat attenuated by time-restricted feeding group, these subjects maintained a 4-hr feeding window and consumed only 1g/kg per day of protein. In two other studies, no such attenuation was found when subjects maintained an 8-hr feeding window and consumed >1.6 g/kg per day of protein. Of course, it’s entirely possible that strength and hypertrophy results from normal feeding windows and time-restricted feeding could become more divergent over longer time courses, or in response to more aggressive caloric deficits or surpluses.
The bottom line: For the time being, evidence would indicate that time-restricted feeding with an 8-hr window is a viable strategy for lifters, provided that they consume enough total protein throughout the day.