TIME RESTRICTION OF FEEDING LEADS TO 17.4% REDUCTION IN FAT MASS WHILE MAINTAINING MUSCLE AND STRENGTH
At least that’s what researchers at the University of Padova claim after conducting an 8-week time restricted feeding (TRF) protocol on resistance trained individuals. Their conclusions indicate that simply restricting the time in which you eat during the day may lead to favorable body composition changes.
The study included 34 resistance-trained males that had been training consistently for at least 5 years. Participants were asked to admit to steroid usage in the past. As a result, 7 individuals were removed from the study due to previous usage.
Subjects were randomly placed into either a Time Restricted Feeding (TRF) group or a Normal Dieting (ND) group. The protocol was as follows:
Each week during the 8-week study, subjects were contacted by a dietician to ensure adherence.
Training was a fairly standard split protocol, allowing for 3 workouts per week on nonconsecutive days.
Unless you’re severely restricting calories in addition to fasting, the evidence does not support the notion that your muscle will fall off the bone if you fast.
Results of the study indicated that the TRF group experienced a significant reduction in fat mass compared to the ND group (-17.4% vs. -2.8%, respectively). The manuscript says -16.4 but I checked the percent change and it’s actually -17.4%.
Strength measurements determined that there were no significant changes in strength for either the bench press or leg press.
My take on the study
Nutritional studies such as this are extremely difficult to control. You’re banking on the subjects:
Both of which typically don’t happen unfortunately.
That doesn’t necessarily mean that the results are moot, however.
If we just assume that a majority of the time subjects did actually follow the timing protocol, it’s safe to say that it was somewhat effective. But it’s not 100% concrete that it’s specifically due to the fact that they were fasting.
While I do believe that there are many benefits of fasting for extended periods of time, there’s a good chance that by restricting their feeding times, the TRF group simply ate less food than that of the ND group.
In the food intake chart (which may or may not be accurate), you can see that the TRF group consumed less food on average compared to the ND group. Further, there was a reduction in circulating leptin for the TRF group, a potential sign of calorie restriction whether intentional or not.
At this point, the only conclusion I can make is that restricting the time in which you eat, may lead to a reduction in total calorie intake.
On the other hand, the TRF group did in fact see no real change in strength and muscle mass, which is contrary to many common ideologies that fasting will cause dramatic reductions in muscle mass and strength. So that’s a plus for fasting.
Unless you’re severely restricting calories in addition to fasting, the evidence does not support the notion that your muscle will fall off the bone if you fast. Especially not in the time frame of 12 to 16 hours.
Lastly, I’d much rather see this protocol being used where both groups intentionally reduced calories. While the authors don’t mention calorie restriction, it’s very likely that the TRF group did, while the ND group did not.
If we really want to say that TRF is effective there are two ways that it should be tested in the future:
I love intermittent fasting. Really, it’s great.
If you would like to try it, it’s likely that there will be no negative impact on muscle or strength if you are simply consuming the same calories in a shorter time frame (time restricted feeding). Doing so will allow you to consume more food, later in the day, which may be nice for cravings sake.
If you choose to intermittent fast AND restrict calories, it can certainly be effective, but you need to ensure that you do so in a reasonable way. Schedule regular re-feeds, eat enough protein and continue to train heavy to maintain strength and muscle.
Also, it's suggested that you base your fasting around when you train in order to maximize the growth/maintenance response as a result of exercise. To learn more, check out my article on training modulated intermittent fasting.
Just know that it may or may not be optimal for maximum strength and muscle growth, to intermittent fast as protein synthesis seems to be optimal with evenly spaced, moderate boluses of protein.
Lastly, take nutritional studies such as this with a grain of salt. At first glance, it seems like a home run for intermittent fasting, but realistically, the results could just be due to calorie restriction and bad dietary reporting.
So is TRF superior? It's hard to say.
Studies such as this certainly shed light on the fact that doing so won’t reduce muscle. However, there’s still the major potential that using TRF simply led to a reduction in calorie intake. Then again, it using a protocol such as this inadvertently leads to calorie restriction, and losing weight is your goal, it may be beneficial to try it out.
If you want to learn more about intermittent fasting, check out my other Intermittent Fasting articles covering the topic.
Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q. F., Battaglia, G., ... & Paoli, A. (2016). 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), 290.
^ Click the link for the full manuscript.
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