The idea that the body can undergo metabolic damage from dieting has been around for many years. The most recent incarnation came from Layne Norton. He claimed, based on hundreds of emails, that he had clients that were either not losing fat or weight on 1200 calories or, better yet, gaining weight.
The fact that 50 years of research contradicts this was irrelevant to him. As a self-proclaimed anti-guru, Layne engaged in every guru game to dismiss the facts. Why? Because money was on the line. Science only matters to him (and others) when it doesn’t hurt the bottom line.
But the fact is that literally every piece of data over 5 decade suggests that his claims are false. The truth of the matter is that people claiming to be gaining weight on low calories are not eating low calories. Rather, they are mis-estimating their calorie intakes. We all told Layne this. He ignored it. Of course now, that his seminar showings have run their course, Layne is posting that the real reason people aren’t losing weight is due to calorie misreporting. It’d be funny if it weren’t pathetic.
In any case, I addressed permanent metabolic damage on this site a number of times and have decided to collect the various questions in one place. Here you go.
Is Permanent Metabolic Damage Real?
Question: Lately I’ve seen a lot of hype regarding metabolic damage that can occur when dieting to very low body fat levels, where individuals permanently “damage” their metabolisms to the point where they are getting fat on 800-900 calories a day. It’s said to occur when losing weight too fast or trying to do too much cardio on top of a very low caloric intake.
This sounds like bro-hype but I’m wondering: Is there any truth to this phenomenon?
Answer: There are several issues at stake here and I’m going to address them in reverse order. Certainly I have seen some weirdness occur (and there is at least one study to support this) where excessive cardio in the face of a large caloric deficit can cause problems, not the least of which is stalled fat/weight loss. In that study, the combination of a very large deficit plus about 6 hours of cardio seemed to decrease metabolic rate more than the diet alone. This is something I intend to cover in more detail at a later date.
This, along with personal observations, was what led me to strongly suggest against doing a lot of cardio on The Rapid Fat Loss Handbook program; in fact I’d say that a majority of failures on that program can be tracked to people trying to do too much cardio and it doing more harm than good. Invariably, the folks who minimize activity (beyond the basic weight workouts) and let the deficit of the diet do the work do better in terms of fat loss. So certainly there is an element of truth to that.
However, we need to look at magnitudes here and do a bit of reality checking. Several in fact.
The first is to look at the food intake. 700-900 calories is not a lot of food and, typically, at the end of a contest diet, hunger is simply off the map. I find it doubtful that someone is truly consuming that little food on a day to day basis at the end of a contest diet.
Note that I did not say impossible (anorexics certainly seem to do this); I’m simply doubtful that someone is consuming that little food in the face of extreme hunger on a day to day basis. They may be reporting that that is their true food intake but I’d be doubtful that it was truly that low on an everyday basis.
Now, as discussed in the Q&A I linked above (as well as in other articles on the site and in my books), there is no doubt that the body undergoes a variety of rather annoying adaptations to reduced calories and fat loss. Reduced metabolic rate, reduced spontaneous activity, etc. all occur and this works to slow fat loss. But what we’re really dealing with here is a magnitude issue.
First and foremost, if someone is claiming to get fat on only 900 calories per day, that implies that their actual total daily energy expenditure is actually LESS than that. That is, as I discuss in some detail in The Energy Balance Equation, we know that to actively gain fat requires a caloric surplus (relative to expenditure).
To gain fat at say 900 calories, and to do so at any fast rate would imply that daily energy expenditure was significantly less than that. For example, assume that someone eating only 900 calories per day were gaining fat at a rate of 1 pound per week. That would imply a 500 cal/day surplus or a total daily energy expenditure of 400 calories per day.
For an average sized male who started out with a maintenance energy expenditure of 2700 calories per day that would be an 85% reduction in energy expenditure. For an smaller female who started with perhaps a 1700 calorie/day maintenance, that would be a 75% reduction from where they started. And simply, that level of reduction is far and beyond everything that’s ever been measured in the history of research on this topic. I mean in 5 decades no such thing has ever been seen.
The Minnesota Semi-Starvation Study
Now, some might argue that the stressors of competition dieting haven’t been examined and they’d probably be right; to my knowledge, no-one has examined the metabolic rate of a bodybuilder following an extreme contest diet. Quite in fact, most studies don’t examine lean individuals at all but there is one study that is possibly relevant which is the seminal Minnesota Semi-Starvation Study.
I’ve talked about this study before and it represents one of the most massively well-controlled studies on the topic ever done (or that will ever be done). In it, war objectors were placed on approximately a 50% reduction from maintenance calories (which only put them around 1500 calories/day or thereabouts in the first place) and were held there for 6 straight months. Activity (walking) was enforced and most men reached the lower limits of body fat percentage by the end of it. I’d note that only men were studied so it’s possible that women, who are prone to showing more resistance to fat loss, could show a differential response.
And the total reduction in daily energy expenditure only amounted to 40% (of which the majority of that was due to the weight loss). Weight and fat loss had basically stopped at the end of the study which makes sense; the original 50% deficit had been reduced to at most 10% due to the 40% reduction in metabolic rate.
The bottom line is that no study I’ve ever seen has suggested that total daily energy expenditure could be reduced to the levels that are implied by ‘gaining fat rapidly at 700-900 calories/day’.
So what’s going on? Certainly some bad hormonal things go on when you combine heavy activity with heavy deficits for extended periods to low body fat levels (I’d note that various types of cyclical dieting such as my own Ultimate Diet 2.0 seem to side-step at least some of this). Thyroid levels drops, nervous system output drops, testosterone levels crater, cortisol goes through the roof.
And I would suspect/suggest that it is this last effect that is being observed and taken as evidence of “metabolic damage”. In a water depleted, glycogen depleted bodybuilder coming out of a contest diet, water balance is going to go absolutely crazy and cortisol is one mediator of this. Water retention secondary to glycogen storage will also contribute.
So you have a situation where a post-contest bodybuilder may be seeing just massive swings in water weight (which can appear like rapid fat gain) following the contest; especially when you consider the normal runaway hunger that tends to occur at that point.
Between glycogen storage and simple cortisol mediated water retention, I can’t see any other reason to explain the observation. Even one day of overeating carbs can cause massive water retention (for example, shifts in water weight of 7-10 pounds over a day or two are not uncommon on cyclical diets) and I suspect that’s what is being observed.
Which is all a long way of saying the following: certainly there is evidence of metabolic derangement when you diet people down to low levels of body fat, this can probably be made worse if you undergo the normal severe overtraining cycle that most dieters go through at that point. But I don’t see any physiological way that true rapid FAT gain can occur at such low calorie levels. I’d suspect that water retention (and a bit of neurosis equating water weight gain with true fat gain) is the primary culprit here.
Can You Cause Permanent Physiological Damage?
Question: I suppose a follow-up question to this answer is just how rare it would be to cross a true “point of no return” where you may have fouled up your internal physiology to where it may never be able to rebound. Or is it usually a case of time and reversing some of the actions that cause it in the first place? i.e. the longer and more extreme the descent, the longer it will take to recover, but recovery is entirely possible
Would clinically severe eating disorders probably be the only instances where someone could allow things to devolve to such a degree that any sort of irreparable damage may have been done to some part of the body and its normal functioning?
Answer: First let me say that I am not and do not claim to be any sort of expert on the topic of eating disorders. It’s simply not been a major area of interest of mine. I think it’s worth considering that what is going on in something like anorexia or bulimia is quite different than what is going on with the topic I was primarily addressing in the original Q&A, to wit contest diets in bodybuilders/physique athletes.
For example, if nothing else we can see massive differences in the nutritional intake of a dieting bodybuilder/physique competitor (typically based around high protein intakes and ‘healthy’ foods) as opposed to the near complete absence of food in the anorexic or the alternation of binging and purging in the bulimic.
With that said, what little literature I have looked at in terms of recovery from eating disorders doesn’t lead me to believe that there is any sort of permanent damage. So long as a “normal” weight is regained (here we’re typically looking at the anorexic), things come more or less back to normal. Even in the seminal Minnesota study, metabolic rate eventually rebounded to normal. Of course the subjects had regained all of the fat they had lost as well for that to occur.
But again, this is really outside of my major sphere of interest; if anyone reading this has expertise that can contribute to this question, I think we’d all love to see it.
How Long Does it Take to Restore BMR?
Question: Layne Norton once said that from the day one begins to eat normally again, it can take anywhere from 3-4 months to completely restore BMR to 100% from post-dieting levels. Although he didn’t cite it, do you know of any studies roughly reflecting this extended time frame? I’m only referring to restoration of normal hormone output and, thus, adaptive thermogenesis, since if the weight loss were maintained, BMR would still be relatively lower than it was pre-diet simply by virtue of a lower final body weight.
Answer: No direct research on this comes to mind immediately although it may exist. I think the problem is that, usually in looking at post-diet “recovery” there is almost always a regain in body fat which tends to color the issue. For example, in the Minnesota study that I mentioned in the question above, following the 6 months of semi-starvation, the men were allowed to eat as much as they wanted. And they went nuts, eating massive numbers of calories and regaining fat. Which normalized metabolic rate eventually but doesn’t really apply to what you seem to be describing.
Frankly, I’m not 100% sure that hormones will ever return to completely normal (see next question) assuming that the lowered body weight/body fat level is maintained. They can be improved by raising calories to maintenance for sure. This is part of the rationale behind The Full Diet Break although that’s really meant to break up periods of explicit dieting (I also suggest it at the end a diet to start normalizing things). Which is a long way of saying “I don’t know” If Layne has a reference for that, I’d love to see it.
Is Metabolic Derangement Permanent Metabolic Damage?
Question: So there is evidence of metabolic derangement, but do you think it is permanent even when returning to normal caloric intake?
Answer: The studies of the post-obese (see next question) suggest that, even at weight maintenance (i.e. when calories have been returned to normal), there is still a small overall reduction in basal metabolic rate (on the order of perhaps 5%) compared to someone who is ‘naturally’ of that weight. Meaning that if you compare someone who is 180 pounds without dieting to someone who has dieted down to 180 pounds, the second person will show a slightly reduced metabolic rate compared to the predicted values. But the effect is slight when calories are brought back to maintenance.
As I discussed in the original Q&A, it looks like the main impact in terms of reducing daily energy expenditure is on spontaneous activity levels; this probably explains why exercise seems to have so much bigger of an impact on weight maintenance than weight loss.
I am unaware of any research examining if this is maintained in the long-term (i.e. will the post-obese continue to show decreases in spontaneous activity). However, the long-term studies of the post-obese (ranging from 2-5 years if my memory serves correctly) suggest that the effect on basal metabolic rate never goes away. So yes, it’s effectively permanent; it’s simply small.
How Long Does it Take for Metabolism to Become Normal?
Question: I’m also wondering about the permanence of any such metabolic adaptations. It seems likely to me that metabolism would return to normal at some point. If so, how long would it take? It seems like I read something about this in a discussion of the Minnesota study, but I’d have to go searching to see if I’m remembering correctly.
Answer: As noted in the question above, what data I’ve seen looking at the post-obese in the long-term suggest that there is a slight reduction in basal metabolic rate that doesn’t appear to ever go away. Studies have examined this for periods up to 7 years and there is always some small impact. Based on what we know about the issue of setpoint I wouldn’t expect this to ever truly go away.
I imagine someone will ask the logical followup to this in the comments which is “So what about people who get and stay lean in the long-term, how do they do it?” Maybe addressing that will get me past my writer’s block to write an actual article about it.
Obese People with Screwed Up Metabolisms
Question: I am a clinical nutritionist at clinic where we see a lot of people with “screwed up metabolisms”. In a different vein, there are the people who got fat from overeating and eating the wrong types of foods and became insulin resistant. Now they have to eat low calorie diets otherwise they gain weight.
One of my clients weighs 360 lbs and her BMR according to the the InBody is 2700 calories. The girl eats maybe 1200 calories a day and maintains that weight. Reversing insulin resistance by eating the proper foods and incorporating resistance training obviously helps. I am wondering if there is an approach to increasing calories systematically when working to reverse insulin resistance without gaining weight?
Answer: This is really a bit outside of what the original Q&A was discussing but I’ll address it anyhow; certainly there can be metabolic derangements that occur in obesity (what’s cause and what’s effect is often hard to determine). However, it’s highly unlikely that your client is truly maintaining her weight on 1200 calories per day if her measured BMR is that high (meaning that her total daily energy expenditure is even higher). Insulin resistance or not, that’s simply a physiological impossibility. And no study shows that it is.
The more likely (and exceedingly common) issue is that she’s simply consuming more food than she’s aware of or self-reporting. Because even in studies of insulin resistance, when calories are reduced (and and accurately monitored), weight/fat loss occurs. So either she’s a physiological anomaly or she’s not really eating 1200 calories per day. And my experience (along with a large body of research) suggests that it’s the latter issue that’s the cause of the problem.