Some Compensatory Mechanisms to Weight Loss
The Body's Responses That Can Hold Us Back and Slow Us Down
This month has been a mini-series on weight loss and some things that happen during the process.
As a quick recap, the series started with a prologue of why it’s important to eat regularly and consistently, followed by a ten-point checklist for anyone to get started on losing body fat and doing so the right way. As you’re likely to know, weight loss will slow down and may eventually come to a halt altogether if we’re not aware of what’s happening and what to do about it, so the second article was troubleshooting these weight loss stalls. Sometimes, though, the process is working, but we can’t see it, so we have the perception of stalling weight loss.
To round out this series, I’d like to review some of the body’s compensatory mechanisms when it’s faced with weight loss, mechanisms that result in a slowing of the progress, further adding to our never-ending-story of frustrations.
The first compensatory mech is this little bugger called metabolic adaptation. Unfortunately, there can be some fearmongering in the health and nutrition space about all this (sounds ironic, and if not ironic, then it still sounds strange: fearmongering about metabolism? Yep, that’s been a thing), and there is a pocket of folks who swear that we can “damage” our metabolisms.
In my view, saying that metabolic damage can occur is a fundamental misunderstanding of what metabolism is, which is the sum of all chemical processes in the body, expressed, as you know, in calories. Calories is simply a unit of heat measurement. So, your metabolic rate is really a measure of how much heat those chemical reactions produce. If you run hot, you’ve either got a faster metabolic rate and/or some extra insulation; if you run cold, you’ve likely got a slower metabolic rate and/or have a little less insulation. (Maybe you’re like me and run cold while having more insulation than you’d like.)
The body’s metabolism is flexible and plastic. It naturally ramps up and down even at different points during the day (that’s a circadian rhythm). If you gain weight, your metabolic rate elevates. If you lose weight, it decreases. Hopefully, this is obvious and makes sense: a bigger body requires more energy to sustain itself as well as to locomote, and the inverse is true for a smaller body.
As you lose weight, your metabolic rate will tick down just because there’s less that’s needed to be done to keep you going. Still, in prolonged or severe energy restriction, the body will tighten its belt and slow things down even more, outside of what would be predicted. One study calls this phenomenon “hibernation mode”1, an energy conservation state. We’re all different, so metabolic adaptation will likely hit two people differently, but the magnitude is often smaller than we’re led to believe, about 6%.2 It’s not huge, but it’s definitely significant—for a person whose resting metabolic rate is 1700 calories, 6% is about a 100-calorie reduction in energy. A hundred cals can go a long way when you’re in an energy deficit and getting hungry.
Fortunately, metabolic adaptation is not permanent and only persists during energy restriction, which is why one article’s title is: “Metabolic adaptation is an illusion, only present when participants are in negative energy balance”3, and as soon as we come back up to our maintenance energy levels, our metabolisms rebound. And if we happen to go into a sustained surplus and/or gain some muscle, it’ll also tick up a bit.
Additionally, there’s a milieu of hormonal responses that occur after prolonged weight loss, such as an increase in ghrelin, which is often referred to as the hunger hormone. More ghrelin is associated with higher appetite levels. As you drop weight, ghrelin increases. Another hormonal response is leptin, which is referred to as a satiety hormone; it signals fullness. As body weight drops, leptin levels also drop.
Already, we have a reduction in metabolic rate—albeit temporary—and altered hormone levels, one that increases appetite and another that decreases satiety and fullness. If weight loss happens too much and/or too quickly, these hormone levels will remain elevated indefinitely, until we’ve regained some weight, basically placating the body.
Hopefully, you’re seeing the body’s response to weight loss makes it an uphill battle.
But wait. There’s more.
Regarding exercise, your body will become more efficient at any activity as you practice it. This efficiency is the result of you being mechanically better at performing movements, essentially better trained, fewer energy leaks and wasted micro-movements, and it’s also the result of the increased muscular and cardiorespiratory fitness. That is, your body becomes more efficient at doing work. You can do more work for less energy. These two factors together, improved mechanical performance and increased fitness, result in what’s referred to as exercise economy, which is one reason why exercise is not to be solely relied on for weight loss.
Other compensatory mechanisms are behavioral and may be either subconscious or conscious. The first and likely subconscious is a reduction in activity, not planned exercise activity but spontaneous non-exercise activity, like doing more chores or just taking another lap around the store if you remembered something you forgot. You might forgo doing little things just because you suddenly don’t feel like it. These micro-activities add up and contribute a meaningful degree of our total daily energy expenditure.
If you have a fitness or activity tracker, check out your total calories at the end of a busy day and compare it to a day of loafing around. For me, this can be a difference of 800 calories, even without exercise. Imagine cutting this number in half, if only for one day. Then a couple. Then most days of the week. You’ve just put the brakes on a major vehicle for energy output.
Another compensatory behavior is the big one, a doozy: compliance. Compliance is another word for “adherence” or “consistency”. Again, this may be subconscious or conscious, and as the authors of one paper note, these actions, decisions, and behaviors are not necessarily volitional4, that is, purposeful, desired, or deliberate choice. Sometimes our compliance is interrupted by other life obligations, responsibilities, and stresses/stressors. We may have time pressures that make it difficult to be consistent with exercise or tracking calories at a meal.
And as I’ve repeatedly referred to my favorite line by NIH researcher Kevin Hall: it’s also the “exponential decay of dietary adherence.”5 It starts off small, a one off here or there, and then it’s acquired into our system.
Again, it’s important to remember that even compliance to consistent energy restriction is affected by the body resisting it. Your body is trying to sabotage your efforts. If you fight it long enough, it will win, which might result in you restaurant hopping or drive-thru parading for a couple of weeks until you’ve regained all of the weight that was lost, and then some.
At this point, hopefully you see how the body doesn’t make this process easy. It fights against our weight loss with:
Metabolic adaptation.
Hormonal changes, especially ghrelin and leptin.
Exercise and activity economy.
Behavioral compensations, such as reducing activity and dietary compliance.
A practical strategy is to focus your efforts for chunks at a time, maybe a few weeks or a couple of months, whatever you seem to be able to handle with relative ease. When the going gets rough and tough, come back to your maintenance energy levels for a while and let your body relax and chill out; let the body’s innate fears of famine and starvation dissipate, which are the drivers of some of these biological, metabolic, behavioral, and cognitive compensatory mechanisms.
For you, maybe this period is one or two days of maintenance energy levels—referred to as a “refeed” in the dieting space. Maybe it’s a week or two—referred to as a “diet break”. Maybe it’s more than a diet break. Maybe you just do a short period of energy restriction, a few days, and when you’re done, you’re done indefinitely, until you’re ready to give it another go. These breaks will make you feel normal, energized, and ready for another round.
Like I said in the ten-point checklist, patience is key, and so is consistency. You want more days on than off, but remember, too, that those “on” days don’t have to be perfect to make progress.
Hopefully, when embarking on a weight loss phase, now you know how and where to start, what to expect, and how and when to intervene.
