Weight loss is generally seen as a positive thing.
It can bring improved health, better looks and all sorts of benefits, both physical and mental.
However, your brain doesn't necessarily see it that way.
Your brain is more worried about keeping you from starving, making sure that you (and your genes) survive.
When you lose a lot of weight, the body starts trying to conserve energy by reducing the amount of calories you burn ().
It also makes you feel hungrier, lazier and increases your cravings for food.
This can cause you to stop losing weight, and may make you feel so miserable that you abandon your weight loss efforts and gain the weight back.
This phenomenon is often called "starvation mode," but is really just the brain's natural mechanism to protect you from starvation.
Fortunately, there are a number of things you can do to help prevent this from happening, so that you can continue to lose weight without torturing yourself.
But before we get to that, let me explain what starvation mode is, and how it works.
What people generally refer to as "starvation mode" (and sometimes "metabolic damage") is the body's natural response to long-term calorie restriction.
It involves the body responding to reduced calorie intake by reducing calorie expenditure in an attempt to maintain energy balance and prevent starvation.
This is a natural physiological response, and isn't really controversial. It is well accepted by scientists, and the technical term for it is "adaptive thermogenesis" ().
I will use the term starvation mode in this article, although it really is a misnomer because true starvation is something that is almost completely irrelevant to most weight loss discussions.
Starvation mode was a useful physiological response back in the day, but does more harm than good in the modern food environment where obesity runs rampant.
Calories In, Calories Out
Obesity is a disorder of excess energy accumulation.
The body puts energy (calories) into its fat tissues, storing it for later use.
If more calories enter the fat tissue than leave it, we gain fat. If more calories leave the fat tissue than enter it, we lose fat. This is fact.
Pretty much all weight loss diets cause a reduction in calorie intake. Some by controlling calories directly (counting calories, weighing portions, etc), others by reducing appetite so that people eat fewer calories automatically.
When this happens, calories leaving the fat tissue (calories out) become greater than the calories entering it (calories in). So we lose fat.
However, the body doesn't see this in the same way as you do. In many cases, it sees this as the beginning of starvation.
So the body fights back, doing everything it can to make you stop losing.
The body and brain can respond by making you hungrier (so you eat more, increasing calories in), but what is most relevant to this discussion here is what happens to the amount of calories you burn (calories out).
Starvation mode implies that your body reduces calories out in an attempt to restore energy balance and stop you from losing any more weight, even in the face of continued calorie restriction.
This phenomenon is very real, but whether this response is so powerful that it can prevent you from losing weight, or even start gaining despite continued calorie restriction, is not as clear.
Bottom Line: What people refer to as "starvation mode" is the body's natural response to long-term calorie restriction. It involves a reduction in the amount of calories your body burns, which can slow down weight loss.
The amount of calories you burn in a day can be roughly split into 4 parts.
- Basal Metabolic Rate (BMR): The amount of calories your body uses to maintain vital functions, such as breathing, heart rate and brain function.
- Thermic Effect of Food (TEF): The calories burned while digesting a meal. Usually about 10% of calorie intake.
- Thermic Effect of Exercise (TEE): Calories burned during physical activity, such as exercise.
- Non-Exercise Activity Thermogenesis (NEAT): Calories burned fidgeting, changing posture, etc. This is usually subconscious.
All 4 of these can go down when you cut calories and lose weight.
It involves a reduction in movement (both conscious and subconscious), and a major change in the function of the nervous system and various hormones (, ).
The most important hormones are leptin, thyroid hormone and norepinephrine, all of which can go down with calorie restriction (, ).
Bottom Line: There are several ways that the body burns calories. All of them can go down when you restrict calories for a long time.
Studies clearly show that weight loss reduces the amount of calories you burn ().
According to a large review study, this amounts to 5.8 calories per day, for each pound lost, or 12.8 calories per kilogram ().
What this means, is that if you were to lose 50 pounds, or 22.7 kilograms, your body would end up burning 290.5 fewer calories per day.
The reduction in calorie expenditure can be much greater than what is predicted by changes in weight.
For example, some studies show that losing and maintaining 10% of body weight can reduce calories burned by 15-25% (, ).
This is one of the reasons weight loss tends to slow down over time, and why it is so difficult to maintain a reduced weight. You may need to eat fewer calories for life!
Keep in mind that it is possible that this metabolic "slowdown" is even greater in some groups that have a hard time losing weight, such as postmenopausal women.
Muscle Mass Tends to Go Down
Another side effect of losing weight, is that muscle mass tends to go down ().
As you may know, muscle is metabolically active, and burns calories around the clock.
However, the reduction in calorie expenditure is actually greater than can be explained by a reduction in muscle mass alone.
The body becomes more efficient at doing work, so less energy than before is required to do the same amount of work ().
So calorie restriction makes you expend fewer calories for the physical activity (whether deliberate or subconscious) that you perform.
Bottom Line: Weight loss and reduced calorie intake can lead to reduced burning of calories. On average, this amounts to about 5.8 calories per pound of lost body weight.
Keep in mind that your metabolism slowing down is simply a natural response to reduced calorie intake.
Although some reduction in calorie burning may be inevitable, there are a number of things you can do to mitigate the effect.
The single most effective thing you can do is resistance exercise.
The obvious choice would be to lift weights, but bodyweight exercises can work just as well.
Studies have shown that resistance exercise, as in exerting your muscles against resistance, can have major benefits when you're on a diet.
In one study, 3 groups of women were placed on a 800 calorie/day diet.
One group was instructed to not exercise, one to do aerobic exercise (cardio), while the third group did resistance exercise ().
Both the women who didn't exercise and those who did aerobic exercise had lost muscle mass, and had a significant reduction in metabolic rate.
However, the women who did resistance exercise maintained their metabolic rate, their muscle mass and their strength levels.
This has been confirmed in many studies. Weight loss reduces muscle and metabolic rate, and resistance exercise can (at least partly) prevent it from happening (, ).
Keep Protein High
Protein is the king of macronutrients when it comes to losing weight.
Having a high protein intake can both reduce appetite (calories in) and boost metabolism (calories out) by 80 to 100 calories per day (, ).
It can also cut cravings, reduce late-night snacking and make you eat hundreds of fewer calories per day (, ).
Keep in mind that this includes just adding protein to your diet, without consciously restricting anything.
That being said, your protein intake is also important to prevent adverse effects of long-term weight loss.
When your protein intake is high, your body will be less inclined to break down your muscles for energy.
This can help preserve muscle mass, which should (at least partly) prevent the metabolic slowdown that comes with weight loss (, 20, ).
Taking a Break From Your Diet Can Help
Some people like to routinely include "re-feeds" where they take a break from their diet for a few days.
On these days, they may eat slightly above maintenance, then continue with their diet a few days later.
There is some evidence that this can temporarily boost some of the hormones that go down with weight loss, such as leptin and thyroid hormone (, ).
It may also be useful to take a longer break, as in a few weeks.
Just make sure to be conscious of what you're eating during the break. Eat at maintenance, or slightly over, but not so much that you start gaining fat again.
Be prepared to gain a few pounds from the added food and increased water weight. This is nothing to worry about.
Bottom Line: Lifting weights and keeping protein intake high are two evidence-based ways to reduce muscle loss and metabolic slowdown during weight loss. Taking a break from your diet can also be useful.
When people start to lose weight, things can happen very quickly in the beginning.
In the first few weeks and months, weight goes down fast and without much effort.
However, things slow down after that. In some cases, weight loss slows down so much that many weeks can go by without any noticeable movement on the scale.
A weight loss plateau can have many different causes (and solutions), and it doesn't necessarily mean that you aren't losing weight.
Water retention, for example, can often give the impression of a weight loss plateau.
This article here lists 15 simple ways to break a weight loss plateau.
Starvation mode is real, but it's not as powerful as some people think.
It can make weight loss slow down over time, but it won't cause someone to gain weight despite restricting calories.
It's also not an "on and off" phenomenon, like some people seem to think. It's an entire spectrum of the body adapting to either increased or decreased calorie intake.
Starvation mode is actually a terribly inaccurate term. Something like "metabolic adaptation" or "metabolic slowdown" would be much more appropriate.
This is simply the body's natural physiological response to reduced calorie intake. Without it, humans would have become extinct thousands of years ago.
Unfortunately, this protective response can cause more harm than good where overfeeding is a much, much greater threat to human health than starvation.