In my first blog post of this 3-installment series, I talked about the concept of "Resting Metabolic Rate" (RMR) or "basal metabolic rate". In this blog post I'll explore that concept in more detail, specifically how it is affected by (extreme) dieting and even some near-starvation studies.
RMR signifies the calories you're burning 24/7, independent of your activity.
The next blog post in this series gives you strategies to increase your resting metabolic rate. In this second installment I consider why so many people fail while dieting, whether dieting increases the risk of "metabolic damage", and much more.
The reason I talk so extensively about the science on this topic is that many people have been yo-yo dieting for years if not decades. A slowed metabolism might explain why it's very hard to lose weight long-term by more extreme dieting and more exercise.
As a result, people have extreme food cravings, feel depressed and have low energy, are stressed 24/7, and sleep poorly.
Surely there's a fix? I'll show you the science on this topic soon! Also, make sure to read some of Alex's writings on this topics, if you hadn't seen them before:
But, back to the concept of resting metabolic rate (RMR). Let's move on to the related metabolic slowdown while dieting, where your RMR potentially goes down a lot:
In this section, I'll explore what happens if you deprive your body of calories for longer periods of time. In the most extreme case, you'll move your body towards (semi)-starvation because you simply need energy to function.
Before you decide on cutting down calories dramatically though, let me tell you a secret:
Dieting has a horrific track record.
So even though you hear about dieting everywhere - on television, from health gurus, and in the gym - that track record exists. Surprise, surprise: dieting does not work for most people in the long-run.
Let me explain.
Even if you manage to lose 20 pounds in 4 months, you've still not lost these pounds permanently.
Short-term success means nothing.
One year after following a diet, 80% of people gain most of the weight they've lost back.[52; 230; 231; 232] If post-diet periods are measured longer than a year, that percentage will probably be higher.
What's even crazier is that dieting - especially losing weight and then gaining weight again - can set you up for more obesity in the long-run.
Now, don't get me wrong, overeating does cause you to gain weight over time - in the sense that you're consuming more calories than you expend. That excess of calories is stored as body fat.
(You'll later learn that overeating alone does not explain the obesity epidemic...)
These factors include:
While you might consider some of these strategies burdensome, you'll ave to implement a significant few of them to be successful in long-term weight loss.
The million dollar question however is why dieting has such as frighteningly poor track record? So let's explore the topic of failure:
A lowered resting metabolic rate is the main type of caloric output that changes after a diet: sure you're burning fewer calories by moving less, but metabolic slowdowns explained by the basal metabolic rate pack the biggest punch.
One instance in which metabolic slowdown occurs is lowering your body fat percentage to extreme levels, which elite athletes often do.[31; 32; 33; 34; 35] Such low body fat levels essentially mimic starvation.
If you experience (extreme) hunger, depression, a loss of your period,
or poor sleep, a very low body fat percentage is not healthy for you
All of these consequences occur because your body senses it's underfed and compensates by turning down many processes in your body.
Even your thinking ability, well-being, and libido will be negatively affected under extreme caloric restriction.
Yes, your body literally shuts down many processes because it thinks it's starving...
But why is there a metabolic slowdown in the first place?
The reason is simple: your body does not like to lose weight. Caloric restriction is stressful, and your body actively tries to prevent fat loss.
If you do engage in caloric restriction you'll almost automatically move less than you'd otherwise do.[114; 115; 116] That decrease in movement occurs on an almost subconscious level, and demonstrates how hard it is to "trick" the body into burning more calories.
So if you use a diet that's really low in calories you can reasonably expect to fidget less, take fewer small walks, and even move your feet less frequently when seated.
In the mitochondria, the energy-producing factories of your cells, energy is lost as heat as a byproduct of energy production if you're on a higher calorie diet--a process which is now reversed.
A bag of cookies or tub of ice cream can be gone faster than the speed of light - and you'll still be hungry...
You'll in fact experience that hunger until your fat-free mass is recovered. But by the time you've recovered your fat-free mass by overeating, you've also added body fat tissue beyond your previous level if you start consuming many calories after a diet.
That's bad news...
In that case, you're worse off than before because you've now gained a few pounds. Another problem is that your basal metabolic rate is now down compared to your pre-weight loss levels, making you gain pounds much more quickly in the future.
And yet, hunger almost literally overtakes you during extreme diets and thus sabotages the results you've worked so hard for. The consequence of that hunger is that many people overeat - even binge eat.
Simple: by depriving yourself of food for weeks if not months your body ingests all the calories it can. And after gaining these new pounds of fat, your body determines that level as the "new normal" - even though you're heavier than before now.
Sorry for the bleak message...
If you gain more fat as compensation after dieting then that's called "fat overshooting".
Fat overshooting is dangerous precisely because an excess of fat is necessarily gained in order for your body to fully restore fat-free mass. The principle of fat overshooting also explains why so many people re-gain their pounds after a period of "successful dieting".
In other words, the hugner only stops after extreme dieting after you've replenished all your fat free mass (and extra body fat).
Keep in mind that metabolic slowdown or damage is not just restricted to one population group. The principle also applies if you've got an eating disorder, for example, which can cause extreme leanness - and backfire in the basal metabolic rate department.
The basal metabolic rate changes due to chronic calorie restriction are called "metabolic adaptations" You may think: "why does my body make such changes at all?"
I often introduce evolutionary arguments in my blog posts. I think there's convincing evidence showing an evolutionary perspective yields new insight into health that would be missed by regular medical studies (for nerds: e.g. randomized controlled trials).
In this case, metabolic adaptations occur as a defense mechanism against future starvation. if your ancestors had very little food 2 million years ago, their bodies increased its ability to store body fat once food stores became plenty again.
That increase in body fat stores boosted your chances for survival.
Remember that during starvation, or living at extremely low body fat percentages (which athletes sometimes do), your body becomes literally more efficient with any calorie that you ingest. Every single calorie you consume generates less heat as a byproduct of energy production, for example.
You'll literally end up with lower body temperatures.
When less heat is generated, your body can allocate more energy to your muscles to hunt. Any process that does not directly help your survival gets shut down, such as libido and spontaneous movement.
Based on the principle of natural section it can be concluded that the mechanism of metabolic adaptations confers a survival advantage--if it did not, ancestors with a strong propensity for metabolic adaptations (as opposed to weak or non-existent) would not have procreated, and you would not be here today.
In plain English: if the possibility of metabolic adaptations did not confer a survival advantage to your ancestors you'd probably not have that ability either...
Extreme dieting is even paired with epigenetic changes.
Epigenetics studies the expression of certain genes.
If you were pregnant and survived the "Hunger Winter" on very little calories in the Netherlands during the German occupation in World War 2, for example, your children have metabolic adaptations that predispose them to greater body fat gains. The obesity-associated health risks would also be higher for your kids.[78; 79]
(I live in the Netherlands)
That experiment was carried out by Ancel Keys, the same physician who later develop the (faulty) theory that saturated fat causes heart disease.
In the Minnesota Starvation Experiment, near starvation conditions were simulated on 36 participants.
The year was 1944.
The experiment lasted one full year.
After a 12 week control period where participants ingested a normal quantity of calories, they were placed on a 24-week starvation (mimicking) period.
Participants were prescribed 1,560 calories per day and physical labor was mandatory as well.
During the starvation period, their food intake simulated that of the concentration camps in Europe. Participants lost 25% of their body weight on average - some even had to quit.
After some time participants began to fantasize about food all day long, and used several strategies to make their food appear more voluminous. Controlling oneself became exponentially harder - many participants sank into depressions.
Even self-mutilation occurred: one participant chopped off three fingers with an axe, but due to an impaired thinking ability could no longer remember whether he had done so intentionally...
Heart rate, sex drive, and strength all declined.
Men had been very healthy no longer were. Still think extreme caloric restriction is the way to go for weight loss?
Fortunately, a 12-week re-feed period followed after the controlled semi-starvation. Participant's response to higher caloric intakes was then investigated.
Some participants had to slowly increase their caloric intake again as part of the controlled experiment--others started to binge eat, expressing nearly insatiable hunger. On average, participants needed about 4,000 calories per day to recover.
When left free, participants ate over 10,000 calories in one day.
The recovery period took years in some cases...
The Minnesota Starvation Experiment perfectly demonstrates what happens during extreme caloric restriction. Even when corrected for fat-free mass losses, semi-starved people end up with lower metabolic rates.
In other words, the loss of muscle mass during starvation cannot fully explain the extent to which your metabolism slows down. Fat-free mass does therefore not exclusively predict resting metabolic rate.
The moral of this section? Think twice about fixing your issues with "eat less and exercise more" - athletes who do so, or people who almost starve due to circumstances need lots of time to recover...
In the end, biology always wins out and you will binge eat on foods to compensate...
Give yourself some credit as well.
Just because you're investing in your health
by reading this blog post!
To summarize the lesson of this section: be aware of metabolic adaptations occurring in response to losing lots of weight.
In the next section, we'll look at metabolic adaptation in people who previously were obese. I turns out obesity and starvation have commonalities...
You already know that once you lose lots of weight, it becomes exponentially harder to have a normal weight again. So if you've ever weighted 300 or 400 pounds, your body "remembers" that weight as "normal".[59; 212]
Building a lean 180 pounds physique will thus be harder if you've ever weighed 400 pounds compared to having had a maximum 200-pound weight in your lifetime - all other variables being equal.
And that's problematic:
A society that convinces you - through Instagram models and TV ads - that caloric restriction is sufficient to attain your ideal body weight does tons of harm.
You probably know yo-yo dieting.
Yo-yo dieters usually lose a ton of body fat, but then re-gain that bodyfat over time (plus more).
The term "yo-yo dieting" does not just refer to a person who loses and regains the weight once--the yo-yo principle is repeated over the course of many years.
The end result is that they're worse off than before because of metabolic adaptations. Every time you're engaging in caloric restriction, your basal metabolic rate slows down. If you regain the weight quickly, you've got a slower metabolic rate and more body fat.
Each time the cycle repeats the problems get worse and worse...
If you've previously been obese it can thus be difficult to retain the results you've worked so hard for. As a formerly obese person, any calorie you ingest is thus much more prone to be stored as body fat.
Let's explain that finding:
If you're obese, your resting metabolic rate is lower than would be predicted according to the Harris-Benedict formula. That lower resting metabolic rate remains after you've successfully lost weight.[38; 39; 40; 41; 53; 110; 111; 112; 113; 124; 163; 203; 213]
(Contradicting studies do exist.[e.g. 209])
Do you know the "Biggest Loser" TV show? On that TV show participants are put on a diet that contains very few calories. That low caloric diet is combined with several hours of exercise per day.
Participants of the "Biggest Loser"ended up with basal metabolic rates that was 700 calories lower than before losing the weight.
You may think: "they just have to recover from the impact of the extreme dieting"
Not at all...
The damage was still present 6 years after the participants finished with the TV program. 700 calories is a lot: 1 big steak contains 670 calories...
Bright side again: with the correct strategies metabolic adaptations are probably reversible. Metabolic damage is thus not permanent.
I do nonetheless feel for people who have lost lots of weight, as they've been guided into a hole due to improper guidance...
But what about if you're healthy and overeat?
Well, some of the excess calories are thus burned off as heat. For that reason, if you just return to a normal eating style after the holidays you'll often lose all the weight again over time.
A hormone called "leptin" is partially responsible for that effect.
(I'll treat leptin in full detail in another blog post).
The more body fat you have, the higher your leptin levels generally are. Body fat exerts leptin into the rest of your body. Leptin signals energy availability. Your brain senses that leptin (if you're healthy), and downregulates hunger once leptin levels are high.[61; 62]
You may thus automatically eat less food after the holidays due to overfeeding the previous days. Combined with an increased basal metabolic rate, the body fat you accumulated after the holidays is thus slowly burned off over time.
In overweight and obese people, however, leptin signaling is off:
The reason for that mismatch is your brain has an inability to sense leptin. That condition is called "leptin resistance". The "hypothalamus" brain area is specifically affected by the leptin.[94; 95; 96; 97; 98]
As a response to dieting your leptin hormone levels can also change for the negative.[43; 107; 108; 109] Due to low body fat, low leptin levels tell your brain that energy is scarce and that you need to find food.
In both obesity and weight loss leptin levels can thus be off.
When your brain correctly senses leptin levels, however, that will help you keep the weight off.[214; 215] I'll return to leptin in the following section. For now, just ask yourself "why is leptin signaling off in the first place?"
I'll let you ponder about that...
So let's return to the previous subject:
The fact that you'll increase your metabolic rate after overeating if you've got a regular body weight should not be glossed over:
To become obese, you'll not only need to eat more than you expend, but you need to increase calorie intake to adjust for the increase in caloric expenditure of an enhanced metabolic rate.
Remember the earlier case in which someone weighed 242 pounds with a basal metabolic rate of 2,300 calories? If they were to increase their weight to 270 pounds, their basal metabolic rate may increase to 2,500 calories.
In that case even more calories are needed to promote future weight gain (or to maintain that body weight). Normally, a negative feedback loop thus prevents you from achieving a 300 or 400 pound body weight.
(Assuming that their other calorie expenditures such as exercise stay the same).
Returning to the Holidays example: if you gain a few pounds around Christmas, your resting metabolic rate may increase with 100 calories per day, allowing you to lose excess body fat over the next couple of weeks.
Additionally, increasing caloric intakes do thus have an effect on obesity.
If you consume just a few percent of calories more than you expend each year, and continue that pattern over long periods time, you'll end up morbidly obese.
As humans have not been underweight or obese for millions of years, body weight is thus tightly regulated under normal circumstances.
I've now ended up with a paradox: over-eating causes you to be obese, but eating less causes metabolic slowdown. The solution to that paradox is found in the next sections.
On another note:
One counterargument against increasing basal metabolic rate is that it's sometimes associated with an increase in mortality. That greater mortality can (partially) be explained because most people with higher metabolic rates are also obese in modern society. Higher metabolic rates are thus not problematic in isolation...
Summarizing this section: fat loss leads to metabolic adaptations in which your basal metabolic rate slows down. That metabolic slowdown makes you more prone to regain the lost weight (and more), but unfortunately almost never accounted for in fat loss advice.
Just think about that...
How many times have you heard a personal trainer say: "it's great you've lost those 50 pounds, but now the real struggle begins"
The answer is probably never, and that's a shame...
Metabolic slowdowns should thus be avoided for long-term fat loss. I'll help you with that problem...
In the subsequent installment, I explore: 1) strategies to increase your basal metabolic rate; 2) how to increase your caloric diet after a diet without gaining lots of fat (to build your basal metabolic rate).
I hope you now see how your resting metabolic rate is very dynamic and not set in stone. Several conditions can also change your resting metabolic rate, and perhaps affect it in the long-term.
In the first installment of this blog post I talked about envisioning the resting metabolic rate as a savings account. Now you hopefully see why. If you follow a diet that is like the Minnesota starvation experiment or the Biggest Loser, with extremely low caloric intakes, problems might emerge.
It's much better to focus on eating sufficient healthy food and applying many other strategies, such as improving the amount of deep sleep you get, moving sufficiently throughout the day, lowering your exposure to noise pollution and air pollution, eating organic foods free of toxins like glyphosate, and more.
Just read the blogs on this website and you'll come very far. Also, make sure to read the third installment of this blog post series that teaches you how to increase your resting metabolic rate according to the latest published science!
This is a post by Bart Wolbers. Bart finished degrees in Physical Therapy (B), Philosophy (BA and MA), Philosophy of Science and Technology (MS - with distinction), and Clinical Health Science (MS), has had training in functional medicine, and is currently a health consultant at Alexfergus.com.
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