Why Does Your Metabolism Slow down After a Calorie Restriction Diet?

Heather Campbell
 min read

Why does your metabolism slow down after a diet that focuses on limiting calorie intake?

Why Does Your Metabolism Slow down After a Calorie Restriction Diet?Why do you burn fewer calories in the months and even years after the diet?

As a general rule, a metabolism slowdown could be due to muscles needing less energy after weight loss, the amount of brown fat decreasing after losing weight, and reduced leptin production, a substance produced by adipose tissue at the time of satiety.

Be sure to read on so you are aware of the medium to long-term consequences of a calorie restriction diet!

Why does your metabolism slow down? Introduction

A slower metabolism does not appear to be due to a change in the energy needed to digest food, nor is it the case that one would burn less by exercising less.

Several studies show that one moves up to 30% more after successful weight loss than before.

This is because weight loss contributes to a positive feeling that makes it physically easier to be active (like walking to the grocery store or climbing the stairs). After a diet, exercise goes typically a little easier.

Related: For more good reasons to lose excess weight, have a read through our other article What Are the Health Benefits of Losing Weight?

Slowed resting metabolism: Illustration

The explanation of why you may suffer from a slowed metabolism after a hefty diet lies with your muscles.

After a weight loss of about 10%, your resting metabolism will slow down by an average of 10 to 15% but not all scientific studies show the same results.

This is probably because there are always differences between different studies regarding how much weight the test subjects lose, how much they exercise, how often they have been on a diet in the past, and what the rest of their lifestyle looks like.

If you experience frequent stress (and/or lack of sleep) after dieting, those lost pounds will be back in no time.

Causes of a slowed metabolism

More efficient use of energy by the muscles

Your muscles become more efficient in terms of using energy after weight loss.

In other words, your muscles can therefore produce the same output with less energy after a strict diet.

The amount but also the activity of brown fat decreases after losing weight

Brown fat is different from our normal white fat. Our brown fat is not in our belly but more around our sternum and near the neck.

Brown fat gives off heat and makes it easier for us to stay warm.

For example, a baby has a lot of brown fat, which is very useful if you come into the world naked. In other words, brown fat functions as a heat source to keep our bodies warm.

The more brown fat you have, the easier it is for your body to warm up again and the less likely you are to get cold.

Someone with a lot of brown fat has a more active metabolism and thus burns better and faster.

They are people who can eat the same amount of calories as we do but remain skin and bones (we all know a few like that).

We can influence the amount of brown fat

Fortunately, we can influence the amount of brown fat we have.

Research showed that we also have a form of intermediate fat called beige fat.

Scientists like Spiegelman showed that one can convert this beige fat into brown fat by exercising (Dana-Farber Cancer Institute, 2008, August 21, Making ‘Good’ Fat From Muscle And Vice Versa. ScienceDaily).

Tip: For more health benefits thanks to exercise, check out our other post Long-Term Health Benefits of Exercise for Our Body and Brain

If your body is often cold, that’s a sign that you need more brown fat.

If you are exposed to cold more often and thus produce more brown fat, you appear to have better insulin sensitivity. And this is very beneficial in preventing type 2 diabetes.

Brown fat is like a warm coat that keeps us warm. So standing under the cold shower for a minute every day already helps produce some more brown fat.

Exposure to cold affects blood sugar levels after only 10 to 11 days. In fact, brown fat requires a lot of glucose and improves and activates the metabolism.

If dieting causes you to lose brown fat, this is detrimental.

Less production of leptin

Leptin is a substance produced by the adipose tissue at the time of satiety.

It tells your brain that you have eaten enough and that you may stop eating (which you do).

After losing weight, many people walk around feeling excessively hungry. In other words, one is less likely to be satisfied or satiated, and one also suffers from a slowed metabolism.

The cause of this could be that because of less fat mass, you produce a little less leptin.

Some experiments also concluded that if you administer leptin artificially to someone with excessive hunger, that excessive hunger decreases.

Unfortunately, it doesn’t always work because there are many people with enough leptin where it seems that the hypothalamus (the satiety center) in the brain no longer picks up the leptin message.

In this case, one speaks of someone who is leptin-resistant.

Thus, after losing weight and eating a hearty diet, one appears to be hungry more often and more than others.

So you are much less likely to be satiated. Even if you consume less energy, you still continue to experience hunger more often.

This lack of satiety usually does not affect your metabolism.

But it does get tricky when you burn less energy and are also more easily hungry.

Because in this way you can very easily fall into a new period of weight gain.

Stress response in the brain

The hypothalamus is a particular regulatory area in the brain. The hypothalamus controls the autonomic nervous system and the endocrine (hormonal) system.

It regulates sexual arousal, hunger, blood pressure, heart rate, stress responses, sleep-wake rhythm, body temperature, and thirst.

Under the influence of stress, a specific area in the hypothalamus reacts by producing the substance CRF (Corticotropin-Releasing Factor).

The adrenal gland is eventually prompted to release extra amounts of cortisol through a chain reaction. Then the thyroid gland goes to work to release more thyroid hormone.

This triggers a series of stress responses, and we experience, for example, an accelerated heart rate.

Medication that artificially lowers our heart rate (such as beta-blockers) for this reason makes us feel tired and, in some people, has the side effect of weight gain. This is a logical consequence because everything slows down.

A short stress response is not detrimental to metabolism and is probably even beneficial.

But long-term stress is another story. It could be that long-term dieting also produces a long-term stress response. In any case, it usually doesn’t make you happy.

Why does your metabolism slow down? Conclusion

After dieting, one often suffers from a slowed metabolism.

There are 3 principal explanations for this:

  • The muscles handle available energy much more efficiently after a diet (and use less energy for the same effort).
  • The amount of brown fat decreases after losing weight. Brown fat functions as an internal heat source. It guarantees a more active metabolism (thanks to brown fat, you burn better and faster).
  • Reduced leptin production, a substance produced by adipose tissue at the time of satiety. The cause of the reduced production of leptin can be explained by the reduced fat mass after dieting.
About Heather Campbell

As a nutritionist, my field of specialization is science-based nutritional advice but more importantly, it is my goal to share capturing and inspiring stories, examples and solutions which can help plus-size individuals overcome their specific difficulties. Read More