Permanent Metabolic Damage – Q&A

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: This seemed a good followup Q&A after last Friday’s Lean Body Mass Maintenance and Metabolic Rate Slowdown – Q&A since it’s semi-related and I seem to have total writer’s block regarding anything approximating a feature article right now.

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.  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.

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 cylical dieting such as my own Ultimate Diet 2.0 and Martin Berkhan’s Intermittent Fasting approach 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.

[FB comments]



18 thoughts on “Permanent Metabolic Damage – Q&A

  1. Hey Lyle, great article.

    Could you elaborate on one thing please.
    When would additional cardio on a cyclical diet like the UD be damaging to your results?
    The study you mentioned…was it 6hrs of cardio a week? That seems possible

  2. Lyle,

    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?

  3. Lyle,
    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. -Chris

  4. So there is evidence of metabolic derangement, but do you think it is permanent even when returning to normal caloric intake?

  5. 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.

    ETA: Oh never mind… I found some info using ‘reduction in thermogenesis after semistarvation’ as a search term. e.g.

  6. 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 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?

  7. Lyle,

    First, let me say, I enjoy your articles and this website very much. I have learned a lot!

    Metabolism crash can be reverse t3, when your body puts on the brakes to prepare for a time when food is scarce – the ancient survival mechanism. To those with a normal metabolism going into a fat reduction plan, the metabolism will recover in a couple of months into maintenance. If someone is prone to auto-immune issues, a low cal diet can tank the thyroid and really kick the reverse t3 into high gear, slowing the metabolism to a crawl. Like you mentioned, water retention and the high cortisol levels make it seem like the weight is coming back or not coming off no matter how low the calories are cut. In normal folks, these things should go away after a couple of months after resuming normal caloric intake. Being aware of the signals of the thyroid not recovering are very important. They can be connected with insulin resistance also. Getting tested for hypo thyroid AND reverse t3 should be considered if the water gain and cortisol continue after a couple of months. People need to be aware that if they aren’t eating much, and can’t lose weight no matter what, they need to get it checked out. Thanks for talking about this.

  8. I wrote like an 8 part series on bodyweight regulation here on the site. Bet I talk about it somewhere there.

    Beyond that, your answer is too vague to get an answer beyond: A duck.

  9. I just found your website. I did find some very good information regarding eating 6 meals a day, why to do this and why not to do this. But once I saw your book about Fat Loss, low calories and using a ketogenic state to lose fat, I got really worried about your advice.

    I have read, and please tell me if I am wrong, that ketosis is horrible because after coming off ketosis the body’s ability to use carbs correctly is severely effected. It often leads to quick, massive weight gains larger than the previous weight loss. The body also is less efficient at losing weight now and that water, lean mass and fat are all lost. I know personally losing lean mass does lead to future fat loss reductions.

  10. The body has a problem with carbs for maybe 24 hours after a ketogenic diet is ended. My first book discusses all of this in excruciatingly painful detail. Basically everything you’ve been led to believe about ketosis is incorrect.

  11. Hi,

    I found this post as I was looking for an answer to the question proposed here.

    I have a friend (actually.) that crash dieted to lose weight, and she now struggles with precisely this permanent metabolic damage. She exercises regularly and only consumes 600 to 1000 Calories a day. This, I assume, is before exercise, but even so, this is far less than a normal person needs for internal energy demand.

    I really just wanted to clarify that such a condition exists.

    Have a nice day.

  12. You noted the Minnesota Semi-Starvation Study and how the control was implemented, but why did you try to draw your own conclusions regarding metabolic damage when that study actually completely covers the topic? The refeeding of the control group…how much they ate and the amount of time that it took for them to recover their normal body weight…was examined in detail and evidence offered that proves intermittent fasting or calorie restriction for any reason will eventually make you very, very fat.

  13. I have restricted calories my entire adult life and gotten up to 250 pounds. I am a woman 5 foot 5. I work out 2 to 3 hours every single day, and i work out HARD and switch it up, cardio, resistance training, classes and so on. I eat 700 – 1400 calories every day.. no dairy… low carbs… mostly just chicken and vegetables and all the good stuff.. I could write a book on nutrition. I am down to 200 pounds and have been stuck for a month now, cannot lose another ounce to save my life, even though I do different exercises, eat different things, take vitamins, drink plenty of water and so on. I track everything I eat. Yes, this absolutely DOES exist.

  14. Yeah, no you don’t. No human can eat that lttle consistently. Like most, with 99% certainty you are misreporting your food intake. And doing so much activity that your cortisol is through the roof. Less cardio, track your food. Stop being crazy.

  15. My conclusions come from far more than that one study. My point is that AT NO TIME did these folks stop losing fat. Which is what was claimed by metabolic damage, that magically fat loss stopped and FAST WAS REGAINED despite low calories. That’s what metabolic damage meant originally. And it’s bullshit.

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