Intermittent Fasting is a TOOL to be used precisely and with caution, especially in trained subjects and is not a viable solution to every bro problem ever.
The table below is from a recent (2016) eight week controlled trial investigating three meals eaten in 8 hours (1pm – 9pm) vs 16 hours (8am – 8pm) in highly trained subjects while on a standardized training protocol.
This paper is an enormous contribution to all of us nutrition meatheads, as most, if not all of the fasting research to date has been in disease states.
The intermittent fasting group tended to eat less calories than the normal eating group, however no statistically significant differences were seen in regards to kcals or macronutrient percentages between groups. With the background set let’s dive into the table of results that I have attached and highlighted up.
You can see not much of anything happened in the normal eating group and nobody really got stronger under either diet regimen, which is a red flag, as the weekly volume of the training protocol was fairly low.
Now, let’s dig into the body comp, metabolic, and hormonal data.
The intermittent fasting group lost about 3.5 pounds of fat and maintained LBM. Sweet.
They also saw a significant reduction in Glucose, Insulin, Triglycerides, and a bunch of inflammatory markers. Awesome.
They also saw a significant increase in HDL and Adiponectin even when controlling for weight loss. Again cool and results that are consistent with the literature on IF.
BUT those on the intermittent fasting diet without caloric restriction had a 21% drop in testosterone (613 ng/dl to 486 ng/dl) and 13% fall off in IGF-1. Also, T3 dropped by 11%, into the LAB LOW range.
This study and abstract were written with an incredibly positive spin in favor of intermittent fasting with quotes like these…
“Based on the present study, a modified IF protocol could be feasible for strength athletes without negatively affecting strength and muscle mass.”
Intermittent fasting with 16 h of fasting and 8 h of feeding, could be beneficial in resistance trained individuals to improve health-related biomarkers, decrease fat mass, and at least maintain muscle mass.
Although, reductions in the anabolic hormones testosterone and IGF-1 were observed, this did not correspond to any deleterious body composition changes or compromises of muscular strength over the duration of the study.”
Come on! This study was 8 weeks and no one got stronger. What would happen at 6 months, 1 year, 5 years? We don’t know, but these significant reductions in anabolic hormones and T3 put up a huge caution sign for me, especially at this light of a training load.
Want to read more? This study is open access. https://www.ncbi.nlm.nih.gov/pubmed/27737674
Also, this study was thoroughly reviewed in the Oct 2016 edition of AARR.