Weight loss is associated with numerous physical and mental health benefits and generally seen as a positive thing.

However, your brain, which is more worried about keeping you from starving, doesn't necessarily see it that way.

When you lose a lot of weight, your body starts trying to conserve energy by reducing the number of calories it burns (1 ).

It also makes you feel hungrier, lazier, and increases food cravings.

These effects can cause you to stop losing weight and may make you feel so miserable that you abandon your weight loss efforts and regain the weight.

This phenomenon, which is your brain's natural mechanism to protect you from starvation, is often called "starvation mode."

This article investigates the concept of starvation mode, including what you can do to prevent it from happening.

What people generally refer to as "starvation mode" (and sometimes "metabolic damage") is your body's natural response to long-term calorie restriction.

It involves the body responding to reduced calorie intake by reducing calorie expenditure to maintain energy balance and prevent starvation.

This is a natural physiological response, and the technical term for it is "adaptive thermogenesis" (2).

The term starvation mode is a misnomer, as true starvation is something that is almost completely irrelevant to most weight loss discussions.

Starvation mode is a useful physiological response, although it does more harm than good in the modern food environment where obesity runs rampant.

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 your fat tissue than leave it, you gain fat. Conversely, if more calories leave your fat tissue than enter it, you lose fat.

All weight loss diets cause a reduction in calorie intake. Some do so by controlling calorie intake directly (counting calories, weighing portions, etc.), while others do so by reducing appetite so that you eat fewer calories automatically.

When this happens, the number of calories leaving your fat tissue (calories out) becomes greater than the number of calories entering it (calories in). Thus, you lose fat, which your body views as the beginning of starvation.

As a result, your 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 they can also affect the number of calories you burn (calories out).

Starvation mode implies that your body reduces calories out 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 it’s so powerful that it can prevent you from losing weight — or even cause you to gain weight despite continued calorie restriction — is not as clear.

Summary What people refer to as "starvation mode" is the body's natural response to long-term calorie restriction. It involves a reduction in the number of calories your body burns, which can slow weight loss.

The number of calories you burn in a day can be split into four components.

  • Basal metabolic rate (BMR). BMR is the number of calories your body uses to maintain vital functions, such as breathing, heart rate, and brain function.
  • Thermic effect of food (TEF). This is the number of calories burned while digesting a meal, which is usually about 10% of calorie intake.
  • Thermic effect of exercise (TEE). TEE is the number of calories burned during physical activity, such as exercise.
  • Non-exercise activity thermogenesis (NEAT). NEAT refers to the number of calories burned fidgeting, changing posture, etc. This is usually subconscious.

Levels of these four measurements can decrease when you cut calories and lose weight. This is due to a reduction in movement (both conscious and subconscious) and major changes in the function of the nervous system and various hormones (3, 4).

The most important hormones are leptin, thyroid hormone, and norepinephrine. Levels of all of these hormones can decrease with calorie restriction (5, 6).

Summary There are several ways in which the body burns calories, all of which can exhibit decreased activity when you restrict calories for a long time.

Studies show that weight loss reduces the number of calories you burn (7).

According to one large review, this amounts to 5.8 calories per day for each pound lost, or 12.8 calories per kilogram. However, this largely depends on how fast you lose weight. Slow and gradual weight loss due to mild calorie restriction does not reduce the number of calories you burn to the same extent (8).

For example, if you were to lose 50 pounds (22.7 kg) quickly, your body would end up burning 290.5 fewer calories per day.

What’s more, the reduction in calorie expenditure can be much greater than what is predicted by changes in weight.

In fact, some studies show that losing and maintaining 10% of body weight can reduce calories burned by 15–25% (9, 10).

This is one reason why weight loss tends to slow over time, as well as why it’s so difficult to maintain a reduced weight. You may need to eat fewer calories indefinitely.

Keep in mind that this metabolic "slowdown" my be even greater in some groups that have a hard time losing weight, such as postmenopausal women.

Muscle mass tends to decrease

Another side effect of losing weight is that muscle mass tends to decrease (11).

Muscle is metabolically active and burns calories around the clock.

However, the reduction in calorie expenditure is greater than what 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 (12).

Therefore, calorie restriction makes you expend fewer calories to perform physical activity.

Summary Weight loss and reduced calorie intake can lead to reduced calorie burning. On average, this amounts to about 5.8 calories per pound (12.8 calories per kg) of lost body weight.

A reduced metabolic rate 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.

Lift weights

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, three groups of women were placed on a diet providing 800 calories daily.

One group was instructed not to exercise, one to perform aerobic exercise (cardio), while the third group did resistance exercise (13).

Those in the groups that either didn't exercise or did aerobic exercise lost muscle mass and experienced significant reductions in metabolic rate.

However, the women who did resistance exercise maintained their metabolic rate, muscle mass, and strength levels.

This has been confirmed in many studies. Weight loss reduces muscle mass and metabolic rate, and resistance exercise can (at least partly) prevent it from happening (14, 15).

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 80–100 calories per day (16, 17).

It can also reduce cravings, late-night snacking, and calorie intake (18, 19).

Keep in mind that you can reap the benefits of protein by simply adding it to your diet, without consciously restricting anything.

That said, adequate protein intake is also important for preventing the 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 or protein.

This can help preserve muscle mass, which should (at least partly) prevent the metabolic slowdown that comes with weight loss (20, 21, 22).

Taking a break from your diet might help | Taking breaks

Some people like to routinely include refeeds, which involve taking 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 the levels of some of the hormones that decrease with weight loss, such as leptin and thyroid hormone (23, 24).

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.

Intermittent fasting might likewise help, although studies have provided conflicting results. Compared with continuous calorie restriction, some studies report that intermittent fasting decreases adaptive thermogenesis, while others show an increase, or a similar effect (25).

Summary 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 might also help.

When you first attempt to lose weight, you may experience rapid results.

In the beginning weeks and months, weight loss can occur quickly and without much effort.

However, things may slow after that. In some cases, weight loss slows so much that many weeks can go by without any noticeable movement on the scale.

However, a weight loss plateau can have many different causes (and solutions), and it doesn't mean that you aren't losing weight.

For example, water retention can often give the impression of a weight loss plateau.

Summary Despite experiencing rapid results when you first attempt to shed pounds, your weight loss may slow or stop altogether. This is known as a weight loss plateau, which can have many causes and solutions.

Starvation mode is real, but it's not as powerful as some people think.

It can slow weight loss over time, but it won't cause you to gain weight despite restricting calories.

It's also not an "on and off" phenomenon. |Rather, it's an entire spectrum of your body adapting to either increased or decreased calorie intake.

In fact, starvation mode is a misleading term. Something like "metabolic adaptation" or "metabolic slowdown" would be much more appropriate.

The effect 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 when overfeeding is a much greater threat to human health than starvation.