Experienced strength athletes lose fat by intermittent fasting, not muscle mass or strength

Strength athletes perform no better or worse if they do time-restricted feeding we wrote yesterday, based on an American study in which the participants did weight training for the first time in their life. In 2016 Italian sports scientists published in the Journal of Translational Medicine their findings from a comparable study. But the Italians used bodybuilders who had at least five years’ experience of weight training. And these bodybuilders reacted a bit differently to the combination of intermittent fasting and strength training than untrained people…

The researchers recruited 34 male bodybuilders in local gyms, all of whom had been doing weight training for at least 5 years. They divided the 34 bodybuilders over two groups. One group ate meals throughout the day [Normal diet; ND]; the other group ate during an 8-hour period of the day [Time-restricted feeding; TRF]. The intermittent-fasting group ate between 1 o’clock in the afternoon and 8 o’clock in the evening.

The researchers got all the participants to do identical training for a period of eight weeks.

Both groups had approximately the same total intake of kcals, carbohydrates, fats and proteins.

Throughout the experiment both groups built up about the same amount of muscle mass and gained about the same amount of muscle strength. There are a few differences in the figure below, but these were not statistically significant.

The difference in effect of intermittent fasting on fat mass was statistically significant: The intermittent-fasting group lost body fat.

Intermittent fasting lowered testosterone and IGF-1 levels, raised the concentration of adiponectin, and lowered the concentration of interleukine-1-beta and of triglycerides in the blood. All of those effects were statistically significant.

“Our results suggest that the modified intermittent fasting employed in this study: time-restricted feed in with 16 hours of fasting and 8 hours of feeding, could be beneficial in resistance trained individuals to improve health-related biomarkers, decrease fat mass, and at least maintain muscle mass,” the researchers concluded.

“This kind of regimen could be adopted by athletes during maintenance phases of training in which the goal is to maintain muscle mass while reducing fat mass.”
“Additional studies are needed to confirm our results and to investigate the long-term effects of intermittent fasting and periods after intermittent fasting cessation.”

Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males


Intermittent fasting (IF) is an increasingly popular dietary approach used for weight loss and overall health. While there is an increasing body of evidence demonstrating beneficial effects of IF on blood lipids and other health outcomes in the overweight and obese, limited data are available about the effect of IF in athletes. Thus, the present study sought to investigate the effects of a modified IF protocol (i.e. time-restricted feeding) during resistance training in healthy resistance-trained males.

Thirty-four resistance-trained males were randomly assigned to time-restricted feeding (TRF) or normal diet group (ND). TRF subjects consumed 100 % of their energy needs in an 8-h period of time each day, with their caloric intake divided into three meals consumed at 1 p.m., 4 p.m., and 8 p.m. The remaining 16 h per 24-h period made up the fasting period. Subjects in the ND group consumed 100 % of their energy needs divided into three meals consumed at 8 a.m., 1 p.m., and 8 p.m. Groups were matched for kilocalories consumed and macronutrient distribution (TRF 2826 ± 412.3 kcal/day, carbohydrates 53.2 ± 1.4 %, fat 24.7 ± 3.1 %, protein 22.1 ± 2.6 %, ND 3007 ± 444.7 kcal/day, carbohydrates 54.7 ± 2.2 %, fat 23.9 ± 3.5 %, protein 21.4 ± 1.8). Subjects were tested before and after 8 weeks of the assigned diet and standardized resistance training program. Fat mass and fat-free mass were assessed by dual-energy x-ray absorptiometry and muscle area of the thigh and arm were measured using an anthropometric system. Total and free testosterone, insulin-like growth factor 1, blood glucose, insulin, adiponectin, leptin, triiodothyronine, thyroid stimulating hormone, interleukin-6, interleukin-1β, tumor necrosis factor α, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides were measured. Bench press and leg press maximal strength, resting energy expenditure, and respiratory ratio were also tested.

After 8 weeks, the 2 Way ANOVA (Time * Diet interaction) showed a decrease in fat mass in TRF compared to ND (p = 0.0448), while fat-free mass, muscle area of the arm and thigh, and maximal strength were maintained in both groups. Testosterone and insulin-like growth factor 1 decreased significantly in TRF, with no changes in ND (p = 0.0476; p = 0.0397). Adiponectin increased (p = 0.0000) in TRF while total leptin decreased (p = 0.0001), although not when adjusted for fat mass. Triiodothyronine decreased in TRF, but no significant changes were detected in thyroid-stimulating hormone, total cholesterol, high-density lipoprotein, low-density lipoprotein, or triglycerides. Resting energy expenditure was unchanged, but a significant decrease in respiratory ratio was observed in the TRF group.

Our results suggest that an intermittent fasting program in which all calories are consumed in an 8-h window each day, in conjunction with resistance training, could improve some health-related biomarkers, decrease fat mass, and maintain muscle mass in resistance-trained males.