|Intermittent fasting has accumulated lots of scientific back-up in obese subjects and rodent models of obesity. In lean, athletic folks, however, the "evidence" is - with one exception - based on hear-say and N=1 reports... until now!|
As the authors likewise point out, the evidence that intermittent fasting (IF) can have significant beneficial effects on blood lipids and other health outcomes in the overweight and obese, albeit mostly using alternate day fasting (learn more), there's limited about the effect of IF in athletes.
Trained individuals such as the thirty-four resistance-trained males (age 29.21 ± 3.8; weight 84.6 ± 6.2 kg) who were randomly assigned to time-restricted feeding (TRF) or normal diet group (ND) in the latest study from the University of Padova.
"The criteria for entering the study were that subjects must have performed resistance training continuously for at least 5 years (training 3–5 days/week with at least 3 years experience in split training routines), be presently engaged in regular resistance training at the time of recruitment, be life-long steroid free, and have no clinical problems that could be aggravated by the study procedures" (Moro. 2016).Time restrictedly fed (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.
|Figure 1: Diet composition and macronutrients distribution at basal level and during the experimental period in both groups as assessed by 7-day food questionnaires (Moro. 2016).|
"The distribution of calories was 40, 25, and 35 % at 1 p.m., 4 p.m. and 8 p.m. respectively for TRF, while ND subjects consumed 25, 40 and 35 % of daily calories at 8 a.m., 1 p.m. and 8 p.m. respectively. The specific calorie distribution was assigned by a nutritionist and was based on the reported daily intake of each subject" (Moro. 2016)What is also important to know is that no snacks between the meals were allowed except 20 g of whey proteins 30 min after each training session. Every week, subjects were contacted by a dietician in order to check the adherence to the diet protocol. The dietician performed a structured interview about meal timing and composition to obtain this information (results see Figure 1) and the exercise part was standardized for both groups, and all subjects had at least 5 years of continuous resistance training experience prior to the study. Training consisted of 3 weekly sessions performed on non-consecutive days for 8 weeks.
|Figure 2: Changes in body composition and strength from pre- to post-study (Moro. 2016).|
- total testosterone and IGF-1 which decreased significantly in TRF after 8 weeks while no significant differences were detected in ND,
- blood glucose and insulin levels which decreased significantly only in TRF subjects and conformingly a significant improvement of HOMA-IR was detected,
- adiponectin which increased, leptin which decreased (but this was not significant when normalized for fat mass), and
- thyroid hormone T3 which decreased significantly compared to ND, without any significant changes in TSH
- TNF-α and IL-1β, two markers of inflammation, which were lower in TRF at the conclusion of the study as compared to ND
- respiratory ratio (RER) which was lowered in the TRF group indicating a relative increase in of fat (at the expense of carbohydrates) to fuel the subjects' energetic demands; demands that stayed 1:1 identical in both groups.
- Gulcelik, N. E., et al. "Adipocytokines and aging: adiponectin and leptin." Minerva endocrinologica 38.2 (2013): 203-210.
- Moro, Tatiana, et al. "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." Journal of Translational Medicine 14.1 (2016): 290.