Metabolism

What is metabolism?

Metabolism refers to the chemical (metabolic) processes that take place as your body converts foods and drinks into energy. It’s a complex process that combines calories and oxygen to create and release energy. This energy fuels body functions.

What does your metabolism do?

Your metabolism never stops, even when your body is at rest. It constantly provides energy for basic body functions, such as:

• Breathing.
• Circulating blood.
• Digesting food.
• Growing and repairing cells.
• Managing hormone levels.
• Regulating body temperature.

What is the basal metabolic rate (BMR)?

Your basal metabolic rate (BMR) refers to the minimum number of calories your body needs to function while you’re resting. This amount varies from person to person. Your BMR fulfills 60% to 70% of the energy your body uses. Rapid weight loss and aggressive calorie restriction decrease your BMR — this is one reason why weight loss is usually not linear and may stall at some point.

How does the body use the rest of its energy?

Your body uses about one-tenth of its energy to process food into fuel. The remaining energy fuels your physical movement.

How does metabolism affect weight?

Many people blame metabolic problems for weight struggles. But your metabolism naturally regulates itself to meet your body’s needs. It’s rarely the cause of weight gain or loss. In general, anyone who burns more calories than they take in will lose weight.

What’s the difference between a fast metabolism and slow metabolism?

Someone with a fast metabolism or fast BMR burns a lot of calories even while at rest. If you have a slow metabolism or slow BMR, your body needs fewer calories to keep it going.

A fast metabolism does not necessarily lead to thinness. In fact, studies show that people with overweight/obesity often have fast metabolisms. Their bodies need more energy to keep basic body functions going.

What conditions affect metabolism?

A few people have endocrine disorders that cause their metabolism to work slower. You may burn fewer calories and put on weight if you have:

• Cushing’s syndrome.
• Hypothyroidism (underactive thyroid gland).

Metabolism can also cause other systemic health problems. Anyone who takes in more calories than they burn will gain weight. This can lead to obesity and related problems like diabetes and metabolic syndrome.

What are metabolic disorders?

Metabolic disorders are conditions that affect how the body processes certain nutrients or enzymes. You inherit a metabolic disorder from a parent. How much you eat or exercise isn’t a factor.

Types of inherited metabolic disorders include:

• Gaucher disease.
• Hemochromatosis.
• Maple syrup urine disease.
• Mitochondrial diseases.
• Tay-Sachs disease.
• Wilson disease.

What other factors affect metabolism or metabolic rate?

Many factors can affect how your metabolism functions. These include:

• Muscle mass: It takes more energy (calories) to build and maintain muscle than fat. People with more muscle mass often have faster metabolisms that burn more calories.
• Age: You lose muscle as you get older, which slows down the metabolism.
• Sex: People assigned male at birth (AMAB) tend to have faster metabolisms than people assigned female at birth (AFAB). They have more muscle mass, larger bones and less body fat.
• Genes: The genes you inherit from your parents play a role in your muscle size and ability to build muscle mass.
• Physical activity: Walking, chasing after your kids, playing tennis and other forms of exercise cause your body to burn more calories than being sedentary.
• Smoking: Nicotine speeds up your metabolism, so you burn more calories. This is one reason people who quit smoking may put on weight. But the health consequences of smoking — cancer, high blood pressure, coronary artery disease — far outweigh any benefit you might get from burning a few extra calories.

How can I have a healthy metabolism?

These steps may benefit your metabolism:

• Don’t skip meals. Your metabolism quickly adapts and starts using fewer calories for body functions. If you restrict calories too much, your body starts to break down muscle for energy. A loss of muscle mass slows the metabolism.
• Fuel your metabolism with fresh fruits and vegetables, lean protein and healthy carbohydrates and fats.
• Strength train or do other weight-resistance type exercises to build muscles.
• Quit smoking. Your metabolism may slow down a bit, but you’ll lower your risk of cancer, heart disease and other problems.

When should I talk to a doctor?

You should call your healthcare provider if you experience:

• Extreme fatigue.
• Unexplained weight loss or weight gain.

A note from Cleveland Clinic

Your metabolism plays a critical role in keeping your body functioning. Certain factors like age, muscle mass and physical activity can affect how your metabolism uses calories for energy. Having a fast or slow metabolism isn’t really a factor in weight gain or loss. Your weight has more to do with calories in versus calories out. Drastically cutting back on calories can have a negative effect on how your metabolism works. Talk to your healthcare provider about other ways to achieve a weight that’s healthy for you.