Can Endurance Athletes Benefit from Time-Restricted Eating?

https://www.ratemds.com/blog/time-restricted-eating-vs-intermittent-fasting/

Fasting is an ancient practice gaining modern-day popularity for its somewhat well-supported benefits for body composition, weight maintenance, and improving indices of cardiometabolic health in healthy and unhealthy adult populations.

Less data are available on how fasting — in particular a kind of fasting known as time-restricted eating, or TRE — affects health and performance in athletes. TRE involves eating all of your daily calories within a specific “eating window”. Some common iterations include 16:8 TRE and 20:4 TRE, where one eats their food for 8/4 hours during the day and fasts for the remaining 16/20 hours.

TRE is a growing area of interest in athletes for a couple reasons. For one, TRE may augment the ability to burn body fat, and thus lead to better changes in body composition (less body fat, more fat-free or lean body mass). Second — TRE may lead to beneficial metabolic adaptations like more mitochondria, better glucose regulation, and an improved ability to use fat for fuel during aerobic or endurance exercise. While plausible, few studies have really provided evidence in humans for any of these benefits.

A new study published in Medicine & Science in Sports and Exercise (MSSE) investigated whether an 8-week regimen 16:8 TRE would produce beneficial improvements in body composition, endurance performance indices, and markers of metabolic health in a group of well-trained male middle- and long-distance runners.

This was a very novel study in that it’s the first to look at TRE’s effects in trained endurance athletes over a fairly long period of time (if one considers 8 months to be long).

One group of 7 males were randomized into a control group — instructed to keep eating their normal dietary patterns for the entire 8-week study. On average, this group had a daily eating window of around 13 hours.

Another group of 10 males were randomized into the 16:8 TRE group — instructed to consume all of their daily calories within an 8 hour eating window, and more specifically as close to between 12pm and 8pm as possible.

Both groups were instructed to maintain their normal training regimen, dietary composition, and other lifestyle habits. No restrictions were put on the amount of food they could eat, only the timing.

Pre- and post-intervention measures included training load, energy intake, macronutrient composition of their diet, endurance performance outcomes including: running economy, speed/oxygen consumption at lactate threshold, and maximal oxygen uptake; body composition measures including: body mass, fat mass, and fat free mass; and metabolic health markers including: glucose, insulin, triglycerides, and HOMA-IR (a marker of long-term glucose control).

Results

• Training load between TRE and control groups was similar throughout the study
• The TRE group tended to eat about ~265 fewer calories at the end of the 8-week period compared to before, but this wasn’t statistically significant
• The TRE group reduced their carbohydrate and fat intake throughout the study (both were lower at 8 weeks in this group compared to baseline)

• Body mass in the TRE group was lower after 8 weeks compared to the control group by around 1.92 kilograms (4.2 lbs)
• Fat mass and fat-free mass were not different between groups
• No differences in any endurance performance parameters were different from pre- to post-intervention or between groups
• No differences in metabolic parameters were observed between groups or from pre- to post-intervention

These findings seem to provide no evidence that TRE is any better for improving endurance performance, body composition, or metabolic health in athletes compared to an “unrestricted” daily feeding window.

Sure — that’s mostly the case. However, this study does have a few limitations that prevent us from completely ruling out TRE as a promising training intervention.

This study wasn’t a “training” study designed to improve performance, and this is something the authors note in the manuscript. The runners maintained their normal training volume/intensity, and weren’t necessarily undergoing a structured program to boost aerobic capacity or specifically target metrics examined in this study.

Some other questions remain to be answered. What would happen if the athletes in the TRE group trained fasted? We don’t know whether they were (some might have, and some might have not), and this could potentially impact some of the study measures and outcomes.

This study does give us some good general information that TRE, when added to a standard training regimen in relatively well-trained athletes, doesn’t really provide any extra metabolic or performance benefit compared to an unrestricted feeding window. Sure, the TRE group lost a bit of weight, but that’s about the only outcome that was significant. For athletes who aren’t necessarily targeting weight loss but rather improved body composition, TRE may not be more efficacious.

Overall, I like the generalizability of this study. For the first time, someone has studied a popular TRE regimen in endurance athletes, leaving us with some questions answered, and others left to be investigated. At this point, whether or not you engage in TRE for athletic performance may be a matter of personal preference rather than a convergence of habits toward the evidence. As always, individual variability in responses and tolerability of training and diet exist, so TRE may in fact seem to work wonders in your lifestyle or training structure.

Sometimes, that’s all the evidence you need as an experiment of 1.

Study cited:

Brady AJ, Langton HM, Mulligan M, Egan B. Effects of eight weeks of 16: 8 time-restricted eating in male middle- and long-distance runners. Medicine & Science in Sports & Exercise. 2020;Publish Ahead of Print. doi:10.1249/MSS.0000000000002488