Training fasted improves lean gains? Surprising new study

Chapters:

00:00 Start

00:22 Background

01:19 Our Study

02:26 Findings: Strength Gains

02:48 Findings: Fat-Free Mass Gains

04:58 Acute Fat Burning Vs Losing Body Fat

06:02 Lower Total Energy Expenditure

06:54 Summary

Transcript:

This was not supposed to happen. Fasted training is not supposed to make anything better. So I was very surprised, a little bit upset even, with the results of our latest study. See, when I spend some of my personal money on a study I just want it to tell me I’m right. So that I can post about it and tell people I told you so. I don’t like surprises, but here we go. So for background, most of the research on fasted training has been quite limited.

There is surprisingly limited long-term, good-quality research on the effects of training fasted versus fed, especially in an energy surplus because almost all the studies on intermittent fasting are done on people in energy restriction when they are cutting. So we know that fasted training is supposed to increase muscle protein breakdown. And it can be limiting for anabolism. However, we also know that there is a compensatory effect when you are fasted for a period of time that anabolic signaling afterwards goes up. So it’s unclear if the acute missing out on a meal and not having protein synthesis during the workout, and probably also having higher rates of muscle protein breakdown if the body can compensate for that over time by having more anabolism after the workout, and kind of catch up with the lost muscle growth.

We also know that fasted training can impair performance. But again, most research is acute. It just looks at people doing a single workout and it does not track what happens over the long-term. So we did a study to find out what the effect is of fasted versus fed training in the long-term. Well, long-term in exercise science view is eight weeks. But we got some interesting results despite being screwed over by the pandemic lockdowns. So what we did is we had a group of strength trained individuals, quite serious lifters, men and women perform an eight-week strength training program, four days a week, full-body workouts, quite high volume, and one group had four meals per day, spread across the day, so four square meals. They trained fed. Whereas the fasted training group had an eight-hour eating window, as opposed to about 13 hours as it turned up for the fed group. And they started eating at least one hour after their workout. So they trained fasted, and they had a shorter total eating window compared to the group with four square meals a day. that trained fed and had their meals spread across the day. Protein intake was approximately one gram per pound or 2.2g/kg in both groups, so should be more than enough to fuel good gains. And energy intake was set at a 10% energy surplus. And we found no significant differences between the groups in at least their reported and logged energy intakes while being under supervision by dietitians. However, more on this later.

And these were our main findings. Strength gains were worse, at least for one hour. arm strength on the squat in the fasted training group. However, there were no significant differences between the groups in terms of leg extension strength, benchpress strength or leg strength. So overall strength training, you could say were worse for the fasted training group, but differences were not that massive. Interestingly, counter to my expectations, fat free mass gains were similar between the groups. We measured fat free miles using a free compartment model, which is quite good. It combines the BOD POD with BIS, which is supposed to give a pretty good estimate of total body composition. We also wanted to do ultrasound measures, but our laboratory got shut down during the pandemic when we wanted to do that after a study so we lost a cohort and some of the data, but we still got decent results. And like I said, a free compartment model is supposed to be quite good. So I don’t expect that this was the major limiting factor for the study. Now here’s where things get very surprising. The fasted training group had equal muscle growth, as measured by a fat free mass as the fed training group. However, they had less fat gain. So in terms of body composition results, they actually got better results, however strength gains were worse.

So what I think happened is that the fasted training group consumed fewer calories, despite reporting the same number of calories. This is called social desirability bias. When you tell people that they are supposed to be bulking, they’re supposed to be in an energy surplus. They actually report that they are, but they don’t do it because, of course, it’s much easier to just say that you’re doing something and not do it than to actually do it. And this is a very common in research, especially when you’re doing an intervention like fasting or a ketogenic diet. And you have people try to bulk, it’s harder for them to increase their energy intake when they are restricting their food choices or the time that they can eat. So often they end up underreporting. I think that’s what happened here. And that this didn’t influence strength gains or muscle growth seemingly is because the effect of energy intake in general is probably quite overrated.

Most prior studies that have looked at the effect of energy intake on muscle growth have found surprisingly small effects, especially as a natural trainee, when you increase energy intake above a relatively small energy supply, most of that surplus just goes to fat gain. There’s only so much muscle you can build, And it seems that that happens in the fed group in our study. So on one hand, you can argue that the fasted training group got better results, but I think that the effect is just, yeah, there was some confounding with energy intake probably. And it does underscore that the fasted training group didn’t get worse gains despite being on a lower energy intake probably. But overall, I would not interpret this as being a better result for the fasted training group. If you look at prior research, it’s very clear that fasted training does not improve fat loss.

This is a very common myth and misconception because when you train fasted, yes, you burn more fat during the workout. But acute fat oxidation does not necessarily translate into better long-term adipose tissue loss. So acute fat burning is not the same as losing body fat long-term. The difference is that long-term fat loss is dictated by energy balance. Because even if you burn more fat during your workout, that means you burn fewer carbs. If you burn more carbs that means you have to resynthesize glycogen, which also costs energy. And in the end, it all comes back to long-term energy balance over time because the body adheres to physical laws, specifically thermodynamics. In the end, energy balance has to balance out. If your total body to energy balance is negative, the body has to get rid of some energy and it can burn either fat or muscle, but it has to get rid of some energy. And as I said, multiple prior studies have found that fasted training does not improve fat loss because it doesn’t improve energy expenditure.

Which brings us to probably the most important finding of the study, in my view, Total energy expenditure was probably actually lower during the fasted workouts because total training volume, total repetition volume was lower during the fast workouts. And we also found that the gap between the groups, so the fed training group had a higher total repetition volume of the same workouts. They managed to, they basically had better strength, endurance, more stamina. And that gap widens between the groups. So over time, the gap between the fed group and the fasted group got bigger and the fed group started outperforming the fasted group more in terms of how many repetitions they could do during their workouts. And we know that repetition volume is a key driver of muscle growth. It’s the primary reason why in some research, higher training frequencies and longer rest intervals improve muscle growth. Thats also why training closer to failure can improve muscle growth.

You do more repetitions, which increases the total accumulated time and retention, which is the primary driver of muscle growth. So basically you do more volume, better performance, more muscle growth. So it’s likely that this gap in performance, the lower training volume of the fasted training group, would start interfering with their long-term gains. In our study, you know, eight week study, small study, we didn’t find this to be statistically significant. But over the long-term, and based on the total research as a whole, the research was clearly negative in terms of strength gains and size gains for fasted workouts versus fed workouts. So I think in our study also that it would likely happen if we were to continue the study longer, even though it seems that the acute effects, the short term effect at least, of fasted training, is not that large for muscle growth. It’s also worth pointing out that the fasted training group also reported lower daily energy levels, which is quite significant for like daily life considerations. But mood and the sleep quality were not affected.

So if you combine lower training volume and lower energy levels, I think that long-term that would lead to less muscle growth in the fasted training group. But the effects are less than I would have expected. And overall in the literature there is a negative trend, but the effects are not major. So I can imagine that some people, if they just really prefer to train fasted or if that helps them, create an energy deficit. and fat loss is your primary aim, then for some reason it might be worth it to train fasted, even though performance will suffer and you are probably long-term going to have slightly worse gains. So I hope this information helps you set up your diet.

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