In a hurry? Have some highlights. (TL;DR)
- Extended caloric restriction can cause reductions in resting metabolic rate (RMR) that persist long after the caloric restriction ends.
- After leaning out or cutting, trainees are liable to regain a good amount of their lost fat if they simply return to their pre-cut level of caloric intake.
- Instead, RMR can be carefully restored by gradually increasing caloric intake in small, discrete steps over a period of weeks or months.
- This strategy, known as reverse dieting, has been used successfully by many trainees to slowly return their caloric intake to pre-cut levels without regaining excess amounts of fat.
In the first installment of this series, I offered some advice—based on both literary and anecdotal evidence—on how to successfully lose body fat while also minimizing the loss of lean body mass (AKA holdin’ on to dem gainz). The question remains, though: what is one to do once they’ve been through this process and have achieved their body composition goals?
A lot of people seem to end up going one of two ways:
- Eager to get back to business as usual, many will jump back to their pre-diet “maintenance” Calories. Only something strange happens once they do: they start gaining weight. “But wait!” they think, “this is maintenance level for me! Why am I gaining weight at maintenance?” We’ll explore why this happens in a moment, but first, what about the others?
- Enjoying the progress they are seeing, the others might reach their original goals and decide they want to lose just a little bit more. And a little bit more. And maybe just a bit more. Before they know it, they end up falling into the hole of perpetual dieting (although this isn’t necessarily an objectively bad thing, depending on that individuals goals and priorities; more on that later!).
Now, let’s explore what happens in each of these scenarios. This is gonna be a dense one.
“I didn’t get that memo.” – Metabolism
Okay. The weight gain. On maintenance Calories. What gives?
Well, as is so often the case, the simplest explanation is probably the most accurate one: that level of energy intake probably no longer constitutes your maintenance level. But why? How is that possible? Because your body has changed! For one thing, you’ve lost weight, and some part of it was metabolically active tissue (i.e. muscle), but that is far from being the whole picture. Over the past decades, it has been demonstrated across several species that caloric restriction can alter resting metabolic rate (RMR for short, since I’m going to be using it a lot). For instance, one study showed that the mean RMR of rats that were calorie-restricted to roughly 60% of the food intake of their control counterparts (rats that were eating as they pleased) was significantly lower than that of the control rats (worth noting that the difference was not statistically significant with 95% confidence until the data were normalized to account for lean body mass differences; illustration of results below).
Okay. What about humans though? The Minnesota experiment—led by Ancel Keys at the University of Minnesota during World War II—is probably the most infamous and extreme example for which we have well-documented data when it comes to humans and energy deficits. The purpose of the experiment was to ascertain the effects of starvation and the reintroduction of food in order to provide insight on how to best treat prisoners of war and others who were suffering from starvation during the war. The basic framework was that 32 male subjects began with 12 weeks on a control diet, followed by 24 weeks of semi-starvation (~50% reduction of energy intake), followed by 12 weeks of restricted refeeding. The study found that RMR (assessed via oxygen consumption) did indeed fall during starvation. After 12 weeks of refeeding, RMRs had increased, but were still below pre-starvation control values.
Another study performed further analysis on the data from the Minnesota experiment and found that these changes in RMR seemed to consist of two main components: 1) a sudden decline in metabolic rate in response to the onset of caloric restriction (this was more pronounced in leaner individuals), and 2) a more gradual decline throughout the starvation phase that was most strongly correlated to the level of depletion of subjects’ fat stores. The simplified interpretation of this analysis is that, perhaps surprisingly, leaner individuals tend to experience more drastic drops in RMR upfront when caloric restriction is implemented, and as one diets down and further reduces their fat stores, this reduction in RMR grows even larger. See below for a demonstrative illustration (this graph is conceptual, not derived from the actual data).
These experiments demonstrate that it is indeed possible for RMR to be reduced during severe caloric restriction (starvation), but how does this carry over to a model that more closely mirrors a typical dieter’s less extreme energy deficit? Enter the biosphere! When unforeseen events caused a shortage of food for subjects that had agreed to live within the confines of the Biosphere 2 facility (an allegedly closed system) for two full years, one group decided to make use of the scenario and study the effects of chronic undereating (the caloric restriction here was much less severe than what the Minnesota experiment had involved) on RMR. Unfortunately, due to the fact that this dietary experiment was a product of circumstance and had not been planned in advance, the subjects, or “biospherians,” as the study called them, were not assessed for RMR prior to entering Biosphere 2, which meant it was impossible to ascertain how RMR was initially changed from baseline at the onset of chronic undereating (we can at least see how their weight changed in the figure below).
What the study was able to show, though, is that upon exiting Biosphere 2, the mean RMR of biospherians was significantly lower than that of a large population of control subjects whose average body weight, body fat %, etc. were similar to what those of the biospherians had been prior to their entering Biosphere 2, indicating that the biospherians’ RMRs had probably been lowered by their time in Biosphere 2. From previous findings, it wasn’t so surprising to see that between two similar populations, the ones (biospherians) who had lost a large amount of weight (largely fat mass) had lower RMRs. What was interesting is that these reductions in RMR were still evident compared to the control population 6 months after the biospherians had been free from the facility and eating ad libitum and, intriguingly, after they had regained back all (if not more) of the weight they had lost during their stay in Biosphere 2. These findings (the initial and persistent decline of RMR during and following caloric restriction and weight loss) have been mirrored in other studies.
What does it all mean?!
Assuming we can all agree that the evidence suggests that the kind of caloric restriction we apply when dieting down to lose body fat can in fact decrease our resting metabolism (especially in cases of long term restriction), we need to next ask, is this a bad thing? What does it even really mean to reduce basal metabolic rate? In a nutshell, with most of the techniques used in these studies, it boils down to the fact that these people are exuding less heat or consuming less oxygen than they previously were. It’s probably easier to intuitively grasp that this happens when a person initiates a caloric deficit at first—less energy in probably means less activity and less heat generated, right? But in the scenario of a chronic caloric restriction where the same caloric deficit is being maintained for a long period of time, how does RMR continue to decline throughout the process?
One way to think about this in a kind of macroscopic, systemic point of view is that the body is essentially using the energy it is provided with more efficiently. We always talk about macronutrients having set amounts of energy (e.g. 4 Calories in 1 gram of carbohydrates), but the way the body utilizes that energy can change drastically depending on its condition and the surrounding environmental factors. One really good example of this came from an ergometric study that measured energy expenditure (via oxygen consumption) during stationary cycling in control subjects relative to subjects that had either gained or lost 10% of their body weight in the weeks leading up to the experiment. Interestingly, they found that subjects who had lost weight (via caloric restriction) had smaller changes in energy expenditure (oxygen consumption) than their control counterparts when they were cycling at low intensities (those who had gained weight showed the opposite effect relative to control). HOWEVER, what’s really interesting (to me, at least), is that these discrepancies in energy expenditure between weight loss, weight gain, and control groups disappeared during higher intensity exercise. While it’s problematic to infer everything from just measuring oxygen consumption on an ergometric cycle, this definitely indicates that there is good reason to include high intensity exercise (I clearly prefer heavy resistance training, but this would also include things like metcon WoDs and HIIT sprints, cycling, etc.) whether you are trying to get lean or stay lean.
This is but one example of how the body’s energy expenditure can be modulate. Another example is mitochondrial uncoupling, where the potential energy built by the electron transport chain for the purpose of generating ATP is instead just expended, or “burned,” for thermogenesis (to make heat in the body; this is one way of helping to maintain body temperature). There are many more examples of ways the body can use or store energy, and there but the point here is this: as we maintain caloric restriction for long periods of time, our bodies appear to “waste” less and less of the energy we nourish them with as heat, which suggests that they are becoming more efficient at harnessing provided energy for processes necessary to survival (i.e. maintaining function of crucial systems while trying to store any extra energy—likely as fat). This effect also appears to persist to some degree even after the caloric restriction is lifted, leading us to an idea that is most often being referred to now as “metabolic damage.”
Metabolic Damage, or the Fountain of Youth?
Whether or not you want to call it “metabolic damage,” hopefully I have convinced you that people can indeed experience persistent reductions of RMR in response to long periods of negative energy balance (this can be achieved through caloric restriction, excessive physical activity, or a combination of the two). Anecdotal evidence suggests that this effect will very likely be more pronounced in people who find themselves in the second of the two scenarios I laid out at the beginning of this article (the chronic dieters/undereaters). Unfortunately, there are a lot of missing pieces when we turn to the literature for answers on what to do about this. For one, we need to know in studies like the biosphere whether or not the subjects’ RMRs eventually adjusted back to what would be predicted for their age, sex, and body composition (they showed that biospherian RMRs were still depressed compared to control averages at 6 months, but what about at 1 year, or 3, or 5?). Another question (really, the main question of this article) is whether or not we can improve the recovery of RMR through dietary manipulation, especially such that we can avoid regaining whatever fat was lost during the caloric restriction that led us to this point (more on that soon).
One important thing to consider before we talk about restoring RMR to pre-restriction levels, though, is whether or not having a reduced RMR is necessarily a negative thing. Of course, it doesn’t seem very desirable to be in a state where you are probably more susceptible to storing excess energy as fat, but it wouldn’t be fair for me to not point out that long-term (actually it’s life-long in most of these studies) caloric restriction has actually been shown to increase longevity in multiple animal models (here are studies done with flies and worms). Why? Well, researchers are still working on that, but a lot of the effects seems to be heavily correlated to intracellular AMP:ATP and ADP:ATP ratios (basically, having less energy directly available as ATP at all times seems to be correlated with increased lifespan…in these short-lived models). One of the hot topic molecules in the spotlight right now is adenosine monophosphate-activated protein kinase (AMPK), which is a highly divergent signaling molecule that is activated during energy challenges to modulate the activity of several growth and metabolism pathways. One common idea about this caloric-restriction-induced increase in longevity is that effects such as the activation of AMPK act to reduce cell growth/division, as such work has shown that the more these animals grow, the faster they age.
Before we get too carried away by these findings, there are a few more things we should probably consider. For one, there hasn’t really been any validation that longer-lived mammals like humans will experience a similar effect on longevity from life-long caloric restriction. Additionally, I don’t think any of these caloric restriction models in animals really account for the effects that the addition of rigorous resistance training have on the longevity equation for us humans. At some point, I want to do a literature review to cover all of the health benefits that come with building juicy, glorious slabs of skeletal muscle, so for now I will just point out unofficially that it is pretty well documented that having ample muscularity (specifically, having a high lean-body-mass-to-fat ratio) correlates well with living a longer, more disease-free life than what you can probably expect if you are sedentary and/or have a high fat-to-lean-body-mass ratio (although these benefits could very well be comparable to the health improvements observed in humans on short-term caloric restriction that are largely due to them just losing a lot of their fat mass). In a nutshell, building muscle generally improves health, and it is hard to build much muscle during times of caloric restriction.
Another pretty important thing (maybe the most important thing) to consider before thinking you should be hopping on the caloric restriction train is that being in an energy deficit is generally just not good for quality of life. One review pointed out that humans practicing caloric restriction lifestyles were prone to depression, irritability, loss of libido, and loss of strength and endurance just to name a few. Of course, this doesn’t mean that no one can be happy living in caloric restriction, and there are many additional considerations, such as what size of a restriction or deficit we’re talking about. Still, unless some evidence comes along that blatantly refutes the idea, I’ll stick with my intuitive feeling that someone who spends most of their time eating around or slightly above what is required to maintain neutral energy balance and building some muscle and strength will generally be pretty darn well off in the health and happiness department. And if you are still really super-duper worried about it, you might be able to have your cake and eat it to, or at least cover some of of your bases by supplementing your diet with resveratrol, which has been shown in some studies to induce effects similar to that of caloric restriction.
Okay. So you’ve finished promoting a caloric deficit and achieved your body composition goals, and now that we’ve done our homework, it’s time to work on restoring your RMR back to pre-restriction levels. We know now that simply eating more will get us moving in the right direction, but we’ve also seen that returning to or even near pre-restriction caloric intake immediately after caloric restriction tends to lead to a rapid regain of lost body weight (fat). Not what we want! So how do we avoid this?
As I mentioned above, the available literature is somewhat lacking when it comes to answering this question. So… Quick! To the anecdote-mobile! If you read the first installment of this series, you know that one of the key pieces of advice I gave on how to lose fat without losing muscle was to make slow, gradual decreases to your caloric intake (you know, don’t be hasty!). From everything I’ve read, it seems like the most effective way to increase your caloric intake without regaining your lost fat following such a caloric restriction is to (surprise!) basically do the same thing, only in reverse. Enter the aptly named practice of reverse dieting, something I was first exposed to from the work of Dr. Layne Norton.
The basic underlying idea is that by gradually raising your caloric intake in small steps, you’re going to slowly bring your RMR upwards at each step while also hopefully avoiding a scenario where your intake grossly overshoots your metabolic demand (because this scenario would likely lead to regain of some fat). Essentially, each caloric increment will introduce a very small surplus to your current “maintenance” intake. Compare this to what happens to someone that finishes their diet, stabilizes, and then adds 500 or 1,000 Calories per day to their current caloric intake. This drastic change will create a large and immediate caloric surplus, which will most likely lead to weight gain. Inevitably, some (if not most) of this weight is going to fat, and all of a sudden, we’re back to square one. On the other hand, a good amount of anecdotal evidence has shown that reverse dieting allows individuals to significantly elevate their caloric intake over time without drastic weight (fat) regain (presumably due to a gradual increase in RMR and a resultant lack of large discrepancies between caloric intake and demand throughout the process).
So, where do we start? If you have successfully dieted down, chances are you have some kind of system in place for making steady, progressive decrements to your caloric intake. This is good, because you are going to be making very similar adjustments on your way back up.
Once you have reached your goals, I’d recommend hanging out at that final caloric intake level for two or three weeks to stabilize somewhat before beginning your journey back to the land of supple calories. After my planned ending time for my cut experiment (which left me eating about 2,300 Calories per day for the last couple weeks), I actually took a week off from lifting to attend a neuroscience conference in Maine (not that taking time off had anything to do with the body composition process; I had just planned to take a break that week to attend the conference). Instead of going overboard trying to perfectly nail my caloric intake during that week, I focused on just eating plenty of meat and not going too crazy on anything else (I’d estimate that I ended up staying pretty close to the 2,300 Calorie mark on most days).
Once I was back home and lifting, I held steady at 2,300 Calories per day for another week (I’m not really a Calorie counter day-to-day; I just returned to eating what I had been eating before the conference) before beginning my reverse diet and bumping my daily caloric intake up by about 100 Calories each week (just by slowly adding rice to lunch one week, adding a banana to my pre-workout meal the next week, etc.). Currently, I’m back up to about 2,600 Calories per day, and my weight hasn’t really budged from 233 lbs (it actually dropped a little bit more the week following the conference; see picture above for “progress”). The plan is to keep progressing upwards slowly (actually making smaller and more gradual increments as I go). Specifically, I am planning right now to switch to holding steady for two weeks at a time at my next couple caloric increments, and after that, I will adjust as needed (either making smaller caloric increments or pushing the time at each increment up to three weeks) based on what happens to my body weight. Why slow down as I go? In a nutshell, because the rate of rate of RMR adaptation to increases in caloric intake probably slows down as we get closer and closer to our original, pre-cut maintenance intake. While I’m not aware of any study that has done very high frequency testing of RMR (most studies seem to just test it at a few mid-diet time marks) over a long period of time during weight loss and/or weight gain to confirm this for sure, the available experimental data have been used by computational modelers to predict the nature of changes in RMR in response to changes in diet.
The figures below show two scenarios: one (top) in which caloric intake is increased by a larger amount, to the extent that energy intake (EI) ends up exceeding the predicted total energy expenditure (TEE) for a long period of time (which means weight regain and probably fat regain), and the other (bottom) in which a smaller increase in caloric intake is implemented, minimizing the amount of time during which EI exceeds the predicted TEE. Now, this is a computational model, and is likely incomplete in its assumptions, but it’s a good place to start us through the thought process.
In essence, we want to aim for something more like the second graph in the cases above, but since we’re talking about starting off our reverse diet at a point where body weight has stabilized (e.g. at the end of a cut), we know that our EI at that point is roughly equal to TEE (otherwise, body weight would still probably be changing). This means that unlike the situation depicted above, as soon as we increase EI, we will probably be exceeding TEE and thus facilitating potential weight gain (whereas the modeled individual above has some “padding” because their TEE is still higher than their EI when they begin to raise their EI). So, the goal then is to increase EI, or energy intake, in small, discrete increments so that EI only exceeds TEE by a small amount during the time that we are waiting for RMR (and TEE) to adapt (increase) in response to the extra energy intake.
The model predicts that a steady increase in energy intake over several months will drive what looks to be a somewhat biphasic increase in TEE in that the rate that TEE raises progressively faster at first and then eventually begins to level out. If this prediction is correct, this basically tells us that we want to allow enough time for TEE adaptations to get in full swing, but after that point, there will be diminishing returns. Since we don’t want to spend years working our energy intake back up (although for some people that have seriously restricted their food intake for several years, it may take many, many months of slow reverse dieting to undue whatever adaptations have occurred), we want to space our incremental increases in energy intake just far enough apart that we allow a good portion of this TEE adaptation to occur. How long this actually translates to waiting between increments probably depends a lot on the circumstances (diet history, hormonal health, body composition, etc.) of the individual and is somewhat guesswork at this point. It might be a big leap to make, but I’m going to make the assumption that even when we are talking about time spans as short as a week, TEE will follow a similar adaptation response as what is predicted over longer durations.
The incremental increases in energy intake that are practiced during a reverse diet, then, might promote sort of micro-cycles of TEE adaptation. I’ve tried to illustrate this hypothesis in the figure below. The important idea here is that while both figures show the individual moving from an intake of 2,000 Calories per day to 2,400 Calories per day, the total amount of energy surplus (the shaded regions) during this process is probably going to end up being higher in the “back to maintenance” scenario than it will be when a reverse dieting strategy is applied. This boils down to the reverse dieter arriving at the same caloric intake as the non-reverse dieter while also regaining less weight in the process.
Again, based on both the predictions of the models above and also on comparisons to other more well understood models of adaptations to perturbations in physiological systems, it seems likely that even with reverse dieting, the rate of RMR adaptation will begin to slow with each caloric increment (the figure below was just to help visualize the idea underlying reverse dieting and doesn’t accurately portray this potential caveat). This is why—as mentioned above—I would recommend increasing the amount of time you stay at each level of caloric intake after you have made your first few increments. I could give you an exact plan in weeks and Calories, but really it will probably be best for you to just monitor what is happening to your body and your weight as you go. If you see your weight begin to increase after an increase, don’t panic; it will probably level out if you just stay at that intake for some time and keep working hard. It’s important to keep in mind that while reverse dieting will minimize weight regain, it won’t completely eliminate it in the journey to restore RMR.
Of course, these are just hand drawn graphs of my hypothesis. I could be completely wrong here. Still, given the widespread anecdotal evidence for the success of reverse dieting in progressively raising energy intake without allowing for excessive weight regain following a restrictive diet, I am inclined to think that even if the details of my hypothesis are misguided, reverse dieting does indeed lead to the outcome that my beautiful graphs predict.
One last consideration about reverse dieting is that the extent to which it will be necessary (or at least prudent) is going to depend on several factors, with the most important two probably being the duration and the severity of the caloric restriction you are reverse dieting out of. Again, at this point I am referencing anecdotal evidence more than anything else, but it appears that the longer you maintain a caloric deficit and the more severe the deficit, the more resilient your metabolic rate will be to change. As is the case when it comes to changing your body in other ways, if you have been grossly undereating for years on end, it is probably going to take a good amount of time and discipline to undo whatever metabolic adaptations have occurred during that time. In these cases, the optimal strategy may be to make even smaller increases in energy intake with longer periods of time in between steps.
Clearly, even with the reverse dieting strategy, we will still hit a point where we can’t really raise our energy intake much higher without gaining weight. How long you decide to spend reverse dieting out of a deficit will be a big determinant in how high you bring your energy intake before you find your new “maintenance” level (remember that this is not a hard-set number). If you don’t want to spend much time moving in small increments, by all means, step your intake up as you need to! Just know that the faster you make these changes, the more prone you are to regaining some of your lost weight. Find the balance that works best for you!
Now that we have all learned about the perils of metabolic adaptation, remember that if you really want to lose weight, your quest isn’t really over until you’ve restored your RMR and avoided regaining the lost weight. So far, the best way we know of to do this is probably reverse dieting. Remember, whether you are in the process of dieting down or reverse dieting your food intake back up, slow, gradual changes are going to give you the most stable (and probably most desirable) results. In short, don’t be hasty!
Let me know if you’ve had trials or triumphs with weight loss/regain in the comments below! Thank you so much for reading, and please, please, please, For the Love of Lifting, sign up for the newsletter (or follow me through the links below) and spread the word!
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- Dulloo, A.G. and J. Jacquet, Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores. The American journal of clinical nutrition, 1998. 68(3): p. 599-606.
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- Hall, K.D., Predicting metabolic adaptation, body weight change, and energy intake in humans. American Journal of Physiology-Endocrinology and Metabolism, 2010. 298(3): p. E449-E466.
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