Does Intermittent Fasting Boost Your Metabolism?

Intermittent fasting is an eating pattern that involves periods of restricted calorie intake (fasting) followed by normal eating.

This pattern of eating could help you lose weight, lower your risk of disease and inhance your lifespan (12).

Some experts even affirm that its beneficial impacts on metabolism make it a healthier way to lose weight than standard calorie restriction (3).

Intermittent Fasting Is Highly Effective for Weight Loss

Intermittent fasting is a simple and very effective approach to fat loss that is comparatively easy to follow (4).

Studies have shown that when it comes to weight loss, intermittent fasting can be similarly effective as traditional calorie restriction, if not more (5678).

In fact, a 2014 review found that intermittent fasting could help people lose an decent 3–8% of their body weight in 3–24 weeks (9).

Additionally, a recent review concluded that in overweight or obese people, intermittent fasting may be a better outlook to weight loss than very-low-calorie diets (10).

Amazingly, this way of eating may also improve your metabolism and metabolic health (1111213).

There are a few different ways to follow intermittent fasting. Some people follow the 5:2 diet, which involves fasting for two days a week. Others practice alternate-day fasting or the 16/8 method.

If you are interested in trying intermittent fasting, you can learn more about it in this detailed guide for beginners.

Intermittent Fasting Increases Several Fat Burning Hormones

Hormones are chemicals messengers that act as messengers. They travel through bloodstream into your body to coordinate complex functions such as growth and metabolism.

They also play an important role in your weight management. This is because they have a strong impact on your hunger, the number of calories you eat and how much fat you store or burn (14).

Intermittent fasting has been associated with improvements in the balance of some fat burning hormones. This could make it a helpful tool for weight regulation.


Insulin is one of the main hormones involved in fat metabolism. It helps in transport of sugar and stores in the form of glycogen also stops your body from breakdown of fats.

Having chronically high levels of insulin can make it much harder to lose weight. High levels of insulin have also been associated with diseases such as obesity, type 2 diabetes, heart disease and cancer (91516).

Intermittent fasting has been shown to be just as effective as other calorie-restricted diets for lowering your insulin levels (171819).

In fact, this eating habit could lower fasting insulin levels by 20–31% (9).

Human Growth Hormone

Fasting can lead to rise in blood levels of human growth hormone, an essential hormone for promoting fat loss (2021).

Some studies have shown that in men, levels of human growth hormone may rise by as much as five-times during fasting period(2223).

Increase in levels of human growth hormone in blood not only support fat burning, but they also maintain muscle mass and have other benefits (24).

However, women don’t always experience the same benefits from fasting like men and it’s currently not clear if women will see the same rise in human growth hormone.


Norepinephrine or noradrenaline, a stress hormone secreted from adrenal medulla that improves alertness and attention, is involved in the “fight or flight” response (25).

It has a variety of other effects on your body, one of which is stimulates fat cells of your body to release fatty acids.

Increases in norepinephrine generally cause larger amounts of fat being available for your body to burn.

Fasting results in a increase in the amount of norepinephrine in your bloodstream (2627).

Short-Term Fasts Boost Metabolism by up to 14%

Many people think that stopping food intake will lead your body to adapt by reducing its metabolic rate to save energy.

It’s well demonstrated that very long periods of fasting can lead to a drop in metabolism (2829).

However, studies have shown that short periods of fast literally increase your metabolism, not slow it down (3031).

One study in 11 healthy men found that a three day fast literally increased their metabolism by a significant 14% (26).

This increase is thought to be due to the increase in the hormone norepinephrine, which promotes burning of fat.

Intermittent Fasting Decreases Metabolism Less Than Continuous Calorie Restriction

When you lose weight, your metabolic rate slows down. Part of this is due to weight loss leads to loss of muscle , and muscle tissue burns calories around the clock.

However, the decrease in metabolic rate seen with weight loss can’t always be explained by the loss of muscle mass alone (32).

Extreme calorie restriction over a long period of time can cause your metabolic rate to slow down, as your body enters in a stage called  starvation mode (or “adaptive thermogenesis”). Your body does this to save energy as a natural defense against starvation (3334).

This has been revealed drastically in a study of people who lost large amounts of weight while participating in the Biggest Loser show on TV.

Participants followed a calorie-restricted diet and heavy exercise program to lose increased amounts of weight (35).

The study found that six years later, most of them had regained approximately all of the weight they had lost. However, their metabolic rates had not returned back and remained around 500 calories lower than you would expect for their body size.

Other studies looking into the effects of calorie restriction on weight loss have found similar results. The lowering of metabolism due to weight loss can be hundreds of calories in a day (3637).

This assures that “starvation mode” is true and can partly explain why many people who lose weight end up regaining it.

Given the short-term effects of fasting on hormones, it’s possible that intermittent fasting may decrease the drop in metabolic rate resulted due to long-term calorie restriction.

One small study demonstrated that losing weight on an alternate-day fasting diet did not lower metabolism over 22 days (17).

However, currently there is no appropriate research available demonstrated the long-term effects of intermittent fasting diets on metabolic rate.

Intermittent Fasting Helps You Hold on to Muscle Mass

Muscle is metabolically active tissue that helps retain your metabolic rate increased. This helps you burn more calories, even at rest (383940).

Sadly, most people also lose muscle along with fat when they lose weight (41).

It’s been declared that intermittent fasting could maintain muscle mass better than calorie restriction because of its effect on fat burning hormones (4243).

Specifically, the increase in human growth hormone noticed during fasting could help maintain muscle mass, even if you’re losing weight (44).

A 2011 review found that intermittent fasting was more effective at preserving muscle during weight loss than a long established low-calorie diet (45).

However, results have been unclear or mixed. A more recent review found intermittent fasting and continuous calorie restriction to have same effects on lean body mass (546).

One recent study found that there is no difference between the lean body mass of people who were fasting and people following continuous calorie restriction after eight weeks. However, at 24 weeks, those in the fasting group had lost less lean body mass (6).

Larger and detailed studies are required to determine if intermittent fasting is more effective at retaining lean body mass.


Although research has shown favourable search outcomes, the effects of intermittent fasting on metabolism are still being investigated (3).

Initial research suggests that short-term fasts enhance metabolism as much as 14%, and several studies recommend that your muscle mass doesn’t reduce much with intermittent fasting (62645).

If this is true, then intermittent fasting has so many important weight loss benifits over diets based on continuous calorie restriction.

At the end of the day, intermittent fasting can be a highly effective weight loss tool for many people.

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