The “Leangains” Intermittent Fasting Study Is Finally Here

There's finally a study examining the effects of Leangains-style intermittent fasting. We have the results and a study breakdown for you here.
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intermittent fasting leangains review

Intermittent fasting (or time-restricted feeding, as it’s typically referred to in the scientific literature) has a long history.  The yearly fluctuations of calorie availability in pre-industrial societies tended to cause (involuntary) periods of fasting; most religions throughout history have practiced some sort of fasting; and today, many Muslims – approximately 20-25% of the world’s populations – forgo all food and water from sunrise to sunset during their holy month of Ramadan.

Until fairly recently, however, few athletes or coaches really gave much thought to intermittent fasting’s applicability for body composition.  Around 2010-2011, interest in intermittent fasting began to increase, remaining strong from 2012 until today.

The name most people automatically associate with intermittent fasting (IF) is Martin Berkhan.  There are other prominent proponents and practitioners of IF, including Brad Pilon, Andy Morgan, Gregory O’Gallagher, Ori Hofmekler (and plenty more), but Berkhan was one of the first to the punch, and it’s his approach to IF – which he’s termed “Leangains” – that has had the most reach and staying power.

The Leangains approach is pretty straightforward: Eat all of your daily calories in an 8-hour window and fast the other 16 hours of the day.  During the fasting window, you can drink zero-calorie beverages (and you can sip some BCAAs around your workout if you have to train in the middle of your fasting window), but restrict anything with any caloric content.  The rest of the specifics of the diet are pretty standard gym advice: high protein, more calories on training days and fewer calories on off days, etc.

Now, you may think about it for a second and realize, “Wait a second.  This just sounds like a glorified way of saying ‘skip breakfast.’ ”


If your feeding window is noon to 8 p.m., you’re essentially just skipping breakfast, eating lunch, tucking in another meal as you’re getting out of work/school, and then eating a late dinner.  That’s really all there is to it. (You can check out the Leangains guide to see how to make the general setup work for your schedule, but really, you can sum it all up with “just skip breakfast.”)

Even though there’s nothing all that exotic about Berkhan’s approach to intermittent fasting, proponents and naysayers both have some very strong opinions about it. Some people say that you’d lose all your muscle by not eating more frequently, and some people say it was a nigh-magical fat-loss “hack.”

Over time, however, most people seem to have gravitated toward a middle-of-the-road position:  IF may be great for some people if it helps them adhere to a diet, but the effects of meal frequency and timing are going to have, at best, a very tiny effect for most people when compared to the effects of total calorie and protein intake.

Until recently, however, there weren’t any studies that investigated Intermittent Fasting, in the way it’s typically practiced, in a group of people who actually lift weights.

The first such study was finally published a couple of days ago.

The participants were mostly in their late 20s or early 30s, and they all had at least 5 years of training experience.

Half of them ate all of their calories in an 8-hour window, with meals at 1 p.m., 4 p.m., and 8 p.m.  The other half ate at 8 a.m., 1 p.m., and 8 p.m. each day.

They recorded their habitual calorie and macronutrient intake at the start of the study and were instructed to maintain those dietary patterns throughout the study in an effort to keep them at caloric maintenance.  There were no significant differences between groups, and calorie/macro intake didn’t change significantly for either group throughout the study.  You’ll see that at 1.8-1.9g of protein per kg of bodyweight, both groups had adequate protein intake for hard training.


They all trained three days per week.  The first session included bench press, incline DB flyes, and curls.  The second session included military press, leg press, leg extensions, and leg curls.  The third session included wide grip lat pulldowns, reverse grip lat pulldowns, and triceps press-downs.  All exercises were done for sets of 6-8 reps to failure, with 3 minutes between sets.

The study lasted for 8 weeks.  At the end of the study, these were the body composition and strength results (in the table below, ND stands for “normal diet”):


As you can see, the only significant effect observed was for fat mass (FM), where the IF group lost about 1.6kg (about 3.5lbs) of fat versus a nonsignificant loss in the ND group.  All that means is that the IF group was in a slight deficit, which isn’t too surprising.  Losing 1.6kg of fat in 8 weeks would require roughly a 200kcal/day deficit, and if you look at the first table above, the IF group was eating about 200kcal/day less than the ND group; they were likely eating a bit below maintenance at the start of the study, and maintained that slight deficit throughout.

I’ll note that the authors of the study propose that the decrease in fat mass in the IF group was likely due to the effects of the hormone adiponectin (which increased in the IF group but not the ND group), which may act in the brain to increase energy expenditure. That may be true, and if it is, that would be a real physiological advantage to IF. But I still think the difference in calorie intake is the more likely explanation, especially since there was no preliminary period to ensure all of the subjects were in neutral energy balance before the start of the intervention.

Everything else relating to strength and body composition was basically identical between the groups.

However, there were some interesting metabolic and hormonal effects of IF.

Testosterone and IGF-1 levels decreased, levels of several pro-inflammatory cytokines decreased, cortisol levels increased, insulin and blood glucose levels decreased, triglyceride levels decreased, T3 levels decreased and RER decreased slightly.  Those are all things you’d expect to see in a calorie deficit.  And while it’s true that the IF group was in a calorie deficit, it was a very small one (less than 10% below maintenance) – probably not a large enough deficit to explain those effects.

On the whole, this study makes it seem that IF “tricks” your body into thinking you’re dieting, even if you’re at (or at least close to) caloric maintenance, in a manner that’s generally consistent with improved health and longevity.

There were no significant or meaningful changes in any of the hormones or biomarkers assessed in the ND group, and neither group experienced a change in basal metabolic rate.

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Here’s the Big Picture of This Study…

If you’re just a bro who’s training to look good and lift heavy stuff, this study lends support to the idea that IF is neither harmful nor a “hack.”  Neither group had a meaningful change in lean mass, muscle thicknesses, or strength.  The IF group lost a bit of fat, but the most plausible explanation is simply that they were in a slight deficit.  If the IF eating pattern fits into your schedule best, then it’s a viable strategy for you.  If you prefer eating breakfast, and that helps with your dietary adherence, there’s probably not a good reason for you to go with IF.

However, this study does provide some evidence that IF may be more beneficial for your health than a traditional meal pattern.  This isn’t a point I’m going to harp on; I’m not a doctor, so it’s not my place.  But for the most part, the changes in the IF group’s blood work are consistent with improved metabolic health and lower chronic disease risk.  This isn’t all that surprising, since various time-restricted feeding and fasting approaches have been shown to have health-promoting effects in previous research (in addition to or independent of calorie restriction and weight loss); however, most of the previous work was on overweight and sedentary populations, so it’s cool to see similar effects in active, young, healthy-weight people.  A lot of that research is linked in the full text of the study at hand if you’re interested in checking it out.

Regarding the health-promoting effects of IF, I largely agree with the conclusion of a review published last year:

“Clinical research studies of fasting with robust designs and high levels of clinical evidence are sparse in the literature. Whereas the few randomized controlled trials and observational clinical outcomes studies support the existence of a health benefit from fasting, substantial further research in humans is needed before the use of fasting as a health intervention can be recommended.”


There are a couple of drawbacks to this study that are worth mentioning:

  1. The participants were all healthy young men, so the results may not be generalizable to other populations (especially women, since there are some metabolic differences between the sexes).
  2. The study lasted 8 weeks, so it doesn’t address the long-term effects of IF.
  3. The participants were at (or at least near) caloric maintenance.  IF and normal meal patterns may have differential effects on strength and body composition in a calorie surplus or deficit that can’t be inferred from this study.
  4. All the nutrition data was based on dietary recall which is … problematic.  But since the participants were supposed to be at maintenance, and their weights didn’t change very much, this probably isn’t a huge issue.
  5. This was a study on Leangains-style IF with an 8-hour feeding window every day.  The results may not be generalizable to other forms of IF, time-restricted feeding, or intermittent energy restriction.

For more reading, I’d strongly suggest this article from Dr. Bojan Kostevski.  It’s a few years old now, but it’s still the best literature review on IF that I’ve come across.

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61 thoughts on “The “Leangains” Intermittent Fasting Study Is Finally Here”

    1. It’s coming! One more SLIGHT delay (since it’s longer than the squat and bench guides, we didn’t bank on how long it would take for editing/formatting/getting pictures/etc.), but I promise it’s on its way.

  1. Greg, is the implication that IF is not a boon for adding lean mass? Decrease in pro-inflammatory cytokines, increase in catabolic t3, decrease in insulin levels, decrease in testosterone – this is the body’s natural response to cutting, but all of these things would suggest that leangains is not necessarily so effective or efficient for making lean gains when compared to traditional cutting and bulking. Can you expand on the implication?

    1. In this study at least, neither group gained muscle, but neither group lost muscle either. It’s possible that you’d see different effects in a deficit or a surplus when the overall diet is set up for muscle gain or fat loss, but on the whole, I don’t think it’s wise to look at hormonal fluctuations *within the normal physiological range* and assume they’re going to affect hypertrophy very much.

  2. While I didn’t dig into the study for more details, it looks like it may have been missing addressing many of the “finer points” of Berkhan’s Leangains approach. Berkhan implements fasted training for certain goals, (with optional BCAA/whey supplementation) macronutrient shifting, (higher carbs on training days), and in general to maximize percentage of daily calories eaten in the post-workout window and maximize time spent in the fasted state when not in a post-workout window. I didn’t see anything here that indicated how the eating schedule/macro breakdown corresponded with training.

    According to Berkhan, his approach helps already lean individuals get even leaner as the fasting and fasted training help with eliminating “stubborn” bodyfat. And the “gains” are maximized by allowing people to overfeed after workouts even when on a weekly caloric balance/deficit (by avoiding eating when not in the post-workout window)

    I would like to see a study that controls for some of these more subtle variables for a population of varying starting BF%’s to test Berkhan’s other reasons to be a proponent for IF.

    1. I agree with this. I’ve done the lean gains thing off and on but in general I think the overall weekly deficit is key. I actually added 36 hour fasts followed by a workout. I honestly was surprised at how much energy I had. My lifts didn’t go up but they held their own.

      Lately I’ve been just eating more but adding serious hikes 2500 ft elevation 5 miles a few times a week. That really has helped me cut some belly fat without the fasts. I still periodically add the fasts in on hike days but I try not to lift fasted as much just because it’s often grueling

  3. What about the literature and research that shows athletes perform better and the other benefits from eating breakfast, especially getting 20-30g of protein upon waking up? Fasting until the afternoon would contradict all of this info

  4. I’m confused as to why the group eating at 8 am, 1 pm and 8 pm had a 12 hour feeding window and 12 hour fasting window rather than the 16/8 methodology?

  5. As someone who was one of the first to be on the IF bandwagon back in 2010 and ran it through 2012, I wish someone would do a long term study on IF.

    I believe it was a huge proponent in adrenal issues I suffered and after talking to other athletes (competitive CF, strongman, and BJJ fighters) who used IF for long term 6+ months they all seemed to suffer the same issues I had from what I originally attributed to over training, but now think was due to IF.

    1. That’s very possible. It’s helpful to think of IF in the context of hormesis (some stress is good and causes positive adaptations, while too much stress is bad and causes fatigue and breakdown). Fasting is a mild stressor. For most people, adding that mild stressor is a good thing, especially if you’re healthy and training volume is fairly low (i.e. this study, and how the Berkhan RPT is set up) – it pushes you further up that hormetic curve. If you’re already fatigued, if training stress is super high, etc. it may do more harm that good, pushing you toward the downslope of the hormetic curve.

      That’s something I didn’t want to get into in the article, because there were a LOT of potential rabbit holes (i.e. if I’m going to get into hormesis, why not also talk about autophagy, or potential disruptions of the HPA axis, etc.) and I didn’t want to turn it into a huge dissertation on IF in general. I mostly just wanted to focus on this study. But in short, I think your observation is on point. For some athletes training super hard (competitive CF and BJJ would definitely fall into this category), IF may do more harm than good.

  6. Testosterone decreased? I’ve always known from sources (Brad Pilon, Cheistopher Walker, etc.) that IF increases Testosterone, GH, etc.

    1. GH, possibly. GH tends to increase with fasting or calorie restriction, though the decrease in IGF-1 here may indicate GH decreased a bit as well (since GH causes IFG-1 release). I haven’t seen any evidence that fasting increases testosterone, though.

      1. Fasting or protein restriction increases GH and decreases IGF-1.
        Stimulation of IGF-1 and insulin by GH is in the fed state.

        Although I would not have expected to see a big increase in GH with 16 hours fasting as opposed to multiple days ditto a decline in IGF-1.

        Maybe repeated IF has a cumulative effect on GH pulse frequency and amplitude? Wouldn’t want to become the pin cushion to test this….

      2. Hey Greg, I have two studies that say fasting increases testosterone, by HUGE amounts, apparently:


        “Short-term fasting (in eight non-obese men) increased the GnRH-elicited LH response by 67% in the non-obese group (LH incremental areas 2147 +/- 304 vs 3581 +/- 256, p less than 0.01), and the corresponding testosterone response by 180% (testosterone incremental areas 111 +/- 61 vs 311 +/- 49 micrograms.l-1.min-1, p less than 0.01).”

        Granted, this study was about 56 hours of fasting, along with a GnRH test at 8 hours and 56 hours into the fasting window.


        This one uses 10 days of water fasting and shows a modest growth in testosterone levels on day 4 of refeeding.

        I think the problem with the first study might be that the testosterone levels were measured after a GnRH test, which is why such a huge surge of 180% was noted. And in the second study, it was overweight men, and they must have lost a lot of fat during this prolonged fasting of 10 days. This would have in turn meant reduced aromatase-induced conversion of testosterone to estrogen, which could explain the modest gains in T.

        That being said, I’m very curious to hear your response on these studies. I’m surprised you hadn’t come across these studies yet.

        1. Unless those (short-term) testosterone increases actually lead to body comp or performance outcomes lifters care about, I honestly don’t find them all that exciting. And I somehow doubt that fasting for 56 hours or 10 days will be beneficial for hypertrophy or strength gains, regardless of the hormonal response.

  7. Very excited to see this article in my inbox this morning.
    TL;DR – I’ve been following an IF-based diet for several years now, and have had recent success with calorie restricted IF+carb-cycling for weight loss while gaining strength (BW:285# to 245. Squat:405# 1RM to 455# 1RM ). IF can be a solution for those that have difficulty with portion control.

    My hunch has been that the efficacy of the IF diet is due mostly, if not all, to calorie restriction (when the goal is fat loss or even maintenance). By not eating breakfast, I’m “saving” myself 750-1500 calories for later in the day. But by the time I actually start eating after training, it’s physically difficult to eat enough to cover my maintenance calories. Additionally, once I start eating, I have always had a difficult time controlling how much I eat. So if I go back to a “normal” eating schedule (like on the weekends when I want to eat breakfast with my kid), I find myself insatiable and just can’t stop eating all day (especially if I’ve been hitting the training hard). I’m sure some of that is due to my “former fat kid” status, and also that I’ve now trained myself to eat large and extended meals during IF. But IF feels like a cheat for me (i.e., I’m going to eat large meals anyway, so if I cut out a meal, the damage is mitigated).

    I also enjoy training fasted, as I feel springier and not weighed down by food. I’m sure my actual performance suffers from it (i.e., I could push myself even further if I had more fuel), but I’ve made pretty good progress in terms of strength and conditioning while following an IF+carb cycling diet for a cut: All mediocre numbers, but I’m happy with a 455#x1 squat, 355#x1 bench, 465#x5 DL, 297 calories on Airdyne in 10min. All this was done at 6’3″, 245# after a ~6 month cut from 285#, when I was squatting 405×1 at beginning.

    1. Ben – those are beastly results, congrats. I also have the former fat kid syndrome, now am an MD working with ppl clinically using IF/carb cycling etc, in process of writing a book – would love to interview you or pick your brain about your process and how it worked for you – Paul

    1. Agreed! Especially when factoring in the beneficial increase in autophagy associated with early dinners & extended periods of time without eating before sleep.

      My challenge with IF was always trying to pack in enough calories & running up against bedtime with a full belly… Not comfortable nor physiologically/metabolically optimal.

  8. Nice article Greg,

    I noticed the control group had a fasting window of 12h. I heard Layne Norton and others talk about protein research that showed, if I remember correctly, 5 feedings of protein was optimal compared to less and more feedings a day for maximising protein syntheses throughout the day.

    Makes me wonder what would have happened if they decreased the fasting window for the control group to say 9 or 10 hours which to me seems closer to what a lot of people who like higher meal frequencies do. I could be wrong but I don’t think a lot of people eat just 3 times a day.

  9. Great study. What I think is interesting anecdotally is most people who do IF or Leangains seem to stick to RPT low volume style workouts, I haven’t heard of many people doing high volume twice weekly splits or anything particularly stressful, possibly pointing to the additive stress of fasting being a little too much – as you pointed out Greg.

  10. Hi,

    the problem about this kind of approach to science is what I call the lack of resynthesis. Put into context real world IF is done quite differently. Some examples in no particular order:

    1. A proper IF-Protokoll starts with an assessment and, if necessary, buildup towards more metabolic flexibility which is one key competency to benefit from an IF-protokoll (read: become antifragile to food intake in the desired range) This experiment is way to short to allow for proper adaptations.
    2. IF is not only the time-restricted food intake the authors referring to. It is not a incidence that Berkhan connected many dods for his method (BCAAs, calorie cycling, carb cycling, biggest meal after a fasted training) and the dods are not connected in this study.
    3. Both groups had no strength gains (no significance!), therefore not muscle mass gain. If you ignore the significance for some speculation purposes the IF group had higher gains.
    4. Additionally: You can tell that the authors have little scientific rigour because they mention the change in RR but it was BORDERLINE to insignificance (p=0.0421) and the effect size is very small. (neglect able).


    1. Just to make sure I’m understanding you right, you think reporting the change in RR shows little scientific rigor because it was only borderline significant and the ES was small, but you think the strength differences should have been mentioned, even though they were even smaller? Since RR only goes from .7 to 1.0 at rest, a shift of .02 represents 6-7% of the total possible variation in that value, and a 15% increase in reliance on fat as a fuel source at rest, relative to baseline. The strength improvements were all 3-4% or less.

      1. No. My point 3 was concentrated on the why of no changes in muscle. They didn’t become (significantly) stronger. The researcher shouldn’t have ignored the significance (in their position) but we are allowed (in a manner of epistemic ethics) for some speculation and fun.

        They reported the shift to more fat reliance without any consideration of the borderline significance. One can make the point, like you did, but should be wary of the context of this statement. It is similar to a doctor who sees a borderline low normal thyroid panel and says that everything is alright because it falls into the normal range.

        1. I have been doing every other day diet for about 3 months. I find it amazing for creating a calorie deficit w/o counting calories. I lift heavy on the days I eat and have lost only 15 lbs but keep losing inches. The thing I find most interesting is I am not fatigued like I was with lean gains style And yet 24hr fasting every other day?? Have you seen any real world people doing it like this and have any more info on it? Because like all the studies no one lifted weights in this study either (the every other day diet) thx

  11. Way late to the party but damn if your website hasn’t become my biggest reference when it comes to the science of becoming a big stroing boi.

    Thanks, mate.

  12. You said the TRF group was eating 200 kcal/day less than the ND group…
    But you didn’t take into account the basal level of each group

    You see… Both groups were in a caloric deficit about of 90 kcal/day within their basal level.

    1. We don’t know that they were at maintenance at baseline, so we don’t know what the 90 calorie decrease from baseline actually means. Calorie/macro assessments are pretty unreliable as well. We can get a better idea of deficits by looking at changes in mass and body comp than from the actual nutritional assessments.

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