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Does Intermittent Fasting Slow Down Metabolism? Busting the Myth

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Kasparas Aleknavičius, MD November 7, 2022

There is a common myth that intermittent fasting slows metabolism.

Don’t be misled by this statement: fasting has plenty of benefits for your overall health and can actually boost your metabolism. Not eating for specific periods may encourage the body to use fat stores for energy, further promoting long-term weight loss.

Intermittent fasting affects your metabolic rate in a good way, depending on the eating windows. This can only happen through safe calorie restriction on a healthy diet. So, how does fasting change your metabolism? Can it really help you lose weight?

In this article, we explain if intermittent fasting slows metabolism.

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What Is Metabolic Rate?

Basal metabolic rate (BMR) refers to the minimum amount of energy your body needs to complete life-sustaining functions, like blood circulation, breathing, or maintaining temperature. Resting metabolism (or resting metabolic rate, RMR) refers to how many calories your body burns in a resting state. The higher your BMR, the more likely you have a fast metabolism that burns extra calories.

Your metabolism is a chemical process that converts food and drinks into energy. Those calories bind with oxygen to give your body fuel. Factors like genetics, age, body weight, gender, diet, and physical activity can affect how fast your metabolism works.

There are several ways you can slow or boost metabolism. Some people perform regular exercise to stimulate those fat-burning chemicals. Others may eat calorie-rich foods, like rice and red meats, to slow their metabolic rate and achieve weight gain.

Just be aware of common triggers that have a significant impact on metabolism. Things like stress, lack of sleep, binge eating, and starvation may damage your metabolic health. It’s always better to look after your body and ensure you eat nutritious foods.

A high metabolic rate is great for losing weight. You don’t need a huge calorie restriction if your body requires those calories to function. Just be mindful that weight loss isn’t just about a fast metabolism; you should continue exercising and eating healthy foods.

Does Intermittent Fasting Slow Metabolism?

Intermittent fasting methods are great for strengthening metabolism. Fasting isn’t about starving yourself but more about changing the times you eat. Your body is encouraged to use fat stores for energy, leading to great weight loss that’s both healthy and safe.

The DoFasting app can make fasting much easier for beginners and pros. You can find 7 of the most popular intermittent fasting periods to try on your fitness journey. Each method comes with tips and tricks to help you lose that stubborn weight.

Let’s take a look at the effects of intermittent fasting on metabolism:

Increases metabolic rate

Short fasting periods push the body to burn fat cells and retain lean muscle mass. It can increase your metabolic rate, further improving the calorie-burning process. Not eating food early in the morning or late at night can stop extra glucose storage.

Only short-term intermittent fasting strengthens overall metabolism. The long-term effects of fasting on metabolism are still being studied. You can try beginner fasting methods, like the 12-hour fast, to feel comfortable during non-eating windows.

Remember that a high metabolic rate can help you lose weight. Your body burns through more calories in the day just to function properly and keep muscles energized. Always start with an easy fast before going into the extended fasting periods.

Effective for weight loss

Different types of intermittent fasting positively impact weight loss. Fasting for longer time frames can encourage the body to burn more fat cells.

A person may lose 7-11 pounds over ten weeks if they follow a calorie-restricted diet alongside fasting. You might drop more weight by doing strenuous exercise, eating low-carb foods, or trying advanced methods like the 24-hour fast.

Just a heads-up: intermittent fasting is healthy when you take the right steps. Never aim to reach starvation mode or not eat for longer than 24 hours. Some people like the challenge of a 36-hour fast, but that doesn’t mean it will help you lose weight safely.

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Promotes fat-burning hormones

Any intermittent fasting method can strengthen fat-burning hormones that boost your metabolism and stimulate weight loss. Each hormone works to reduce body fat when you’re not consuming too much sugar or carbs.

Below, you’ll find the three main hormones that fasting affects:

  • Human growth hormone
  • Insulin
  • Norepinephrine

The human growth hormone (HGH) may decrease fat storage and increase lean muscle mass. Fasting boosts this type of hormone up to 300% after just three days. Your pituitary gland also releases HGH to build and repair muscles after weight training.

Intermittent fasting has been known to reduce insulin resistance during a non-eating window. The body needs insulin to keep blood glucose in a safe range (100 mg/dL after an 8-hour fast). Not eating for 16 hours can also maintain normal insulin production.

Many types of fasting can increase the amount of norepinephrine in your bloodstream. This hormone supports healthy blood pressure and increases the heart rate. A greater level of norepinephrine could encourage your body to burn more fat.

Having more of these hormones will encourage further weight loss. Your metabolism is on high alert when losing weight and using fatty acids for energy. Always monitor your calorie intake and follow an eating pattern that feels comfortable and healthy.

What Slows Down Your Metabolism?

One thing to note is that fasting does not slow your metabolism but boosts it. Some conventional calorie-restricted diets may have different effects on your metabolism. A good example is the ketogenic diet which involves low-carb foods.

Eating minimal carbs and fatty foods can encourage the metabolism to burn fat for energy instead of glucose. However, some people make the mistake of severely restricting their calories, which leads to a slower metabolism in the long run.

Intermittent fasting is a better weight loss method if you stick to eating a good amount of calories. You don’t want to fall into the trap of continuous calorie restriction when removing carbs. Always monitor your food intake to prevent starvation mode.

There are many other factors that weaken metabolic functions. This could be skipping meals with high-protein content. Protein can increase metabolism by 20-30% after nutritious meals, which helps to strengthen the thermic effect of food (TEF).

Not getting enough physical activity is another big reason. A sedentary lifestyle decreases the amount of calories you burn in 24 hours. If you want to lose weight, go for a long walk or try to move around when you’re working from home all day.

Should You Try Fasting Now?

Intermittent fasting isn’t for everyone, including people who might have certain health problems. Pregnant or breastfeeding women should stay away from this fat loss method, as it can stop proper development due to the lack of daily calories.

Those who have experienced past eating disorders may need to avoid fasting. Calorie restriction for long periods can disrupt your mental health and possibly trigger another eating disorder. It will be best if you stick to a regular eating pattern that contains healthy foods.

Specific health problems, like cardiovascular disease or digestive issues, may not work well with intermittent fasting. Periods of fasting can disrupt your body’s natural functions and create symptoms of constipation, headaches, low blood sugar, and bloating.

People who do extensive weight training may not benefit from fasting. They need a continuous food supply to fuel their muscle growth. If you don’t eat for a long period of time in the morning, you might start losing lean muscle mass instead of fat.

Some doctors may recommend you stay away from fasting while taking medication that requires food consumption. It’s not worth damaging your health or ruining the effects of medication, so only try intermittent fasting while not taking prescription drugs.

If you have any of these problems or physical factors, find another weight loss method that strengthens fat metabolism. A dietitian can point you in the right direction that’s healthy for your body. Some low-calorie diets may be better in your specific case than fasting.

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Conclusion

So, does intermittent fasting slow metabolism?

Fasting doesn’t slow down metabolism or disrupt your resting metabolic rate. It can actually increase the fat-burning process. If you want to lose that extra bit of weight, try to eat fewer calories to use more energy expenditure through rest.

Remember not to try fasting if you have specific health problems. Metabolism slows if you suffer from a weakened immune system. Avoid very low-calorie diets and always seek professional advice when learning safe weight loss methods.

Author

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Kasparas Aleknavičius, MD
  • Head of Medical Affairs at Kilo Health
  • Medical Doctor at Vilnius University, Lithuania
  • Partnering with the EU-funded Young50 and EUPAP projects

Kasparas Aleknavicius is a medical doctor that graduated from Vilnius University, working as head of medical affairs at Kilo Health. After nearly 5 years in the industry, Kasparas focuses on digital health and is looking for innovative ways to help people lead healthy lifestyles through digital health and wellness platforms.

You can find Kasparas on LinkedIn and follow his latest research on Medium.

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