18 June 2020
Refeeds for fat loss: Are they worth it?
Refeeds have been a staple fat-loss strategy for a long time now, but until very recently we’ve been working with only hypotheticals and anecdotal support for their effectiveness in lean and athletic populations. This specific line of research just began in March 2020, with a study from Campbell et al. (3)– is this the dawn of…
Refeeds have been a staple fat-loss strategy for a long time now, but until very recently we’ve been working with only hypotheticals and anecdotal support for their effectiveness in lean and athletic populations. This specific line of research just began in March 2020, with a study from Campbell et al. (3)– is this the dawn of a new age for sports nutrition?
Prolonged hypocaloric diets bring with them a host of negative adaptations metabolically, hormonally, and psychologically. Literature reviews over the years (8,12)have identified a disproportionate decrease in resting metabolic rate than would be expected based on lower body mass, lower thermic effect of food (from simply eating less), and increased mitochondrial efficiency as key components of metabolic adaptation. Changes in circulating hormones with extreme weight loss – such as during a bodybuilding contest prep – threaten regulation of metabolic rate (decreased thyroid hormones), maintenance of muscle tissue (increased cortisol and decreased testosterone), and large increases in hunger (decreased leptin and increased ghrelin) (12). Further, long diets tend to cause increases in drive to eat (10)and cravings, decreases in non-exercise activity thermogenesis and willpower, and worst of all – the dreaded state of being constantly hangry.
“Intermittent energy restriction” (IER) or “non-linear dieting” are umbrella terms that essentially mean not having the same calorie deficit every day. We know that energy balance is ultimately what governs body weight changes, but there are many ways to set up a diet aside from the plain and boring identical daily deficit. Refeeds, diet breaks, various fasting protocols, and more are all tools at our disposal – the grapple, smoke pellets, and batarangs in our utility belt, if you will.
The main idea of IER strategies is to stave off some of the negative adaptations that make weight loss harder and weight regain easier. They’re not going to eliminate the drive to eat due to having become a much leaner version of yourself, nor do they seem to boost metabolic rate or leptin levels to a meaningful degree (4,5). But all is not lost! Hypothetically, periods of higher food intake (particularly from carbs) should allow for less muscle protein breakdown, greater glycogen restoration, and improved mood, which should lead to better performance in the gym and recovery thereafter, leading to better maintenance of muscle mass by the end of the diet. The occasional increase in food also offers a psychological break, which should improve overall adherence by siphoning off some of the restriction you’ve been feeling, allowing you to more easily engage in social events and giving you a chance to fit larger portions or different food choices into your day. Sounds like a pretty good deal… so does it work?
To date, nearly every IER intervention has (understandably) studied overweight and obese individuals, and the results largely suggest that continuous diets and intermittent diets lead to very similar outcomes (1,7,11). Probably the most widely known study in this realm is the MATADOR study (2), which showed greater fat loss and less decline in resting energy expenditure when alternating between 2 weeks in a deficit and 2 weeks at maintenance as compared to a continuous dieting group, despite taking twice as much time. Although it’s possible that there were some unreported adherence issues in the continuous group or perhaps differences in activity levels, the MATADOR study gives us some cause for optimism in applying these sorts of strategies to athletes.
The MATADOR study used 14-day maintenance periods interspersed within the diet, which we would normally term a “diet break.” A refeed on the other hand, typically lasts only 1-3 days. If benefits are seen when using refeeds, that’s a very good thing because it would allow us to get in and out of the diet in less total time, which makes it easier to meet deadlines like a competition date and simply cuts down on the time spent in a deficit. There’s a good amount of logic and anecdotal support behind refeeds, but now we have experimental evidence to reckon with also; let’s see what the data say.
Campbell et al. (3)split subjects into two groups. One group used 2-day refeeds at the end of each dieting week. Consequently, the other 5 days in the week had to be more aggressive to match the overall deficit in the continuous dieting group. Two weeks of food tracking preceded the intervention to establish maintenance calories, from which the calorie deficits were calculated. The refeeds were implemented via an increase in carb intake.
Subjects were randomized into one of the two diet configurations and underwent a 7-week training program typical of how physique competitors normally train. Measures of body mass (BM), fat mass (FM), fat-free mass (FFM), dry fat-free mass (dFFM – subtracting water weight off from FFM), and resting metabolic rate (RMR) were collected before the intervention and at the end of the 7thweek (for the continuous dieting group) or 48 hours after the end of the 7thweek (for the refeed group). The purpose of waiting 48 hours was to eliminate differences in FFM based on glycogen and water weight from the refeeds. This can account for a significant amount of mass, as approximately 500g of glycogen can be stored in skeletal muscle, each gram of which is surrounded by around 3g of water (9)– when we’re expecting to see only small, if any, changes in FFM, you can see how that could easily become an issue in accurately observing true changes.
Both groups lost a significant amount of BM and FM to similar degrees. The more notable things are RMR, FFM, and dFFM, which will require a little bit of statistical jargon to address (don’t be scared).
The refeed group did not experience a significant change in RMR or FFM. The continuous group saw a significant decrease in both, although the change in FFM had a miniscule effect size (not practically meaningful) and the change in RMR had an effect size that just barely crossed the threshold into a “small effect.” In fact, the RMR difference was around 40 calories per day, which is well within the range of nutrition label inaccuracy anyway, so nothing to get excited over. But here’s the rub – neither of those differences popped up in the ANOVA (a method used to identify how changes in one variable affect changes in others) as a significant group x time interaction. This means that we can’t say the discrepancies in FFM and RMR were due to which dieting group the subjects were in; it must be due to some other factor. There was, however, a group x time interaction for dFFM, in which the refeed group retained, on average, 1.7kg more dFFM than the continuous group. How can we explain these results?
A key point to this study is that the refeed group did not get their post-test measurements done until 48 hours after their final refeed. While that was a great idea in concept, the final refeed was the final day of the study – meaning that the subjects had 48 hours of free living leading into post-testing. It’s unlikely that the subjects dropped back into their previous 35% calorie deficit for those 48 hours of their own volition; more likely, they were eating at maintenance or possibly even above. Post-testing could have conceivably taken place at the end of a 4-day refeed for the refeed group, while the continuous group was testing at the end of their 49thstraight day of dieting, which easily could affect the RMR and FFM results. For the dFFM: a common complaint with measures of FFM is that it includes a bunch of stuff other than muscle, so here we see an improvement in the sense that water mass was taken out of the equation. The refeed group retained ~1.7kg more dFFM, but let’s keep our skeptical hats on for a moment longer. Water may have been subtracted out, but changes in glycogen weren’t accounted for. Up to hundreds of grams of glycogen could influence the statistical significance of the results by making the difference in dFFM between groups even smaller. To top it off, the refeed group would have entered post-testing with substantially more food residue in their GI tract, which would have gotten lumped into the dFFM measurement also. An alternative design could have involved post-testing being done right before the final back-to-back refeeds. To match for total time, maybe we just have both groups diet for 6 weeks and 5 days, but that way we might get a better snapshot of the real effect (or lack thereof) of refeeds.
I painted a pretty gloomy picture there, but I want to also acknowledge the possibility that refeeds do actually help you retain muscle during a diet. Considering the limitations of this study, we should be pretty cautious saying that we have scientific evidence for muscle retention, but we still have sound logic and a whole lot of coaches and lifters willing to vouch for refeeds. I’m not quite ready to completely give up on the idea that refeeds could acutely improve training performance (even if only due to psychological benefits), which over time could improve the look of your physique. I can totally see a scenario where refeeds help you feel better and train harder, and even if it’s all in your head, I still call that a worthwhile pursuit. If it works, it works.
For now, we need to lean on experience, logic, and anecdote until more data get published looking at different refeed setups. As things currently stand, refeeds seem like a cool strategy to get a psychological benefit, improve adherence, and maybe an acute performance boost. In terms of adherence, having a refeed or two on the weekend might be a good option for people who tend to be very social, unlike myself who is basically a hikikomori (if you didn’t have to Google that word to know what it means, I salute you). In terms of energy and recovery for training, things are a bit unclear. Glycogen takes a while to be restored, so perhaps scheduling a refeed one or two days prior to a very high-volume workout would be helpful if you train the same muscles very frequently. But on the other hand, resistance training isn’t going to fully deplete your glycogen except for some very unique and extreme circumstances, and by the time you train that same muscle group again it will have had plenty of time to replete anyway. It might make more sense to consider putting refeeds on the days of your hardest training sessions; that way you can have a larger pre-workout meal, feel awesome and happy, perform at your very best, and have bountiful substrate available to kickstart the recovery process. In contrast to placing a refeed on the day when you have the highest training workload, you could instead place it on a rest day. When you’re out and about doing cardio in the morning, going to work or school, and hitting the gym on the way home, your mind is so occupied that the diet probably doesn’t feel that difficult. But what happens on Sunday when your rest day from the gym and a day off from work/school coincide? Those days when the refrigerator is calling your name every couple of hours are often the hardest, so if that example hits a little too close to home, you might find success giving yourself more food on your rest day to make adherence easier.
Also, not everyone should use refeeds. Some people may actually get worse results due to the psychological effect of that high-calorie day. Imagine you’re in a very dark cave; it takes a while, but eventually your eyes adjust and you can see fairly well. Then, someone runs past you holding a bright torch. For a moment, everything is lit up and you can see perfectly, but seconds later the light is gone and your eyes need to re-adjust while you’re reminded of just how very dark the cave actually is. Refeeds can act this way for some people. A day of higher carbs only serves to remind them how hungry and deprived they feel the rest of the week, setting them up for much more mental anguish than they otherwise would have endured. Another possibility is that the refeed disrupts their momentum and habits, kicks them out of their tunnel vision, and potentially even triggers a binge. Refeeds, like everything else in this game, must be individualized.
If you do decide to implement refeeds, it’s important to keep a couple of things in mind. One is that the more you increase your calories on refeed days, and the more refeed days you program, the less calories you have available for the rest of the week (to match total weekly intake). There’s a balancing act to be played here. Also, as pointed out in a recent review (6)discussing the possible utility for refeeds and diet breaks in physique competitors, it makes sense to use the least amount of refeeds that net you the most benefit; don’t over-do it. Every day spent refeeding is a day spent not in an energy deficit, extending the overall timeframe of the fat-loss diet. For the overweight or obese looking to get healthier, that’s not much of an issue, but for bodybuilders in prep (or, just lean people in general), the diet is like crossing a vast desert. You can take occasional sips of water (refeeds), which help make the trip less unpleasant, but at the end of the day you’re still in the desert – don’t drag it out longer than you need to.
This area of research is very much in its infancy, and there is so much room for more data to be collected. Before we get too excited brainstorming, we need some data definitively showing a physiological benefit… but we can still brainstorm a tiny bit. What happens if we test different timescales (1 vs. 2 vs. 3 days) or magnitudes (reaching into a mild surplus vs. a large surplus vs. maintenance)? Maybe having two refeeds back-to-back has different effects than having one refeed every 3-4 days (for the same weekly average calories). What if we time those refeeds to coincide with the hardest training days, or the days before the hardest training days, or on rest days? If nothing else, we have the power to apply intermittent dieting in countless ways to improve psychology and adherence, and aren’t they the foundation of everything anyway?
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