Many people assume that metabolism is the process that determines whether they gain or lose weight, but this is somewhat misleading. Metabolism is not necessarily responsible for burning fat. Instead, it is a complex process in which the body converts food and drink into energy that is used for many functions, including circulating blood, breathing, and repairing cells.

What Determines Metabolism?

Many things determine metabolism. Men generally burn more calories than women because they have less body fat and more muscle. Younger people burn more calories than older people as the amount of muscle decreases and the amount of fat increases. Just about everything the body does requires energy and contributes to metabolism.

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Anabolism and Catabolism

There are two types of metabolism: anabolism and catabolism. Anabolism is constructive. It supports cell growth, maintains and repairs tissue, and stores energy. During this process, small, simple molecules become large and complex. Catabolism is destructive, breaking down large molecules of fat and carbohydrates to release energy. The energy from catabolism heats the body, moves the muscles, and fuels anabolism.

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Endocrine System

Hormones released by the endocrine system control metabolism. For example, the pituitary gland releases growth hormone — which stimulates growth and development — and antidiuretic hormone that controls water retention in the kidneys, among many others. The pancreas releases glucagon to raise blood sugar levels and insulin to lower them. Insulin also stimulates the breakdown of fat, protein, and glucose.

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Weight Gain

Weight gain is complicated, and it is not always the result of a slow metabolism. People with medical conditions like Cushing's syndrome or hypothyroidism can be adversely impacted by a slow metabolism, but generally, it is not to blame for weight gain. More likely contributing factors are genes, diet, environment, sleep, stress, and exercise.

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Metabolism Myths

There are many myths about metabolism. For example, some people believe that exercise increases your metabolism, but the increased calorie burn only occurs during the exercise and for about an hour afterward. Building muscle boosts metabolism slightly, but not enough to make a significant difference. Some foods, including caffeine, hot peppers, and green tea, raise metabolism slightly, but not enough to cause weight loss.

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Metabolism and Exercise

In many cases, people who believe they have a fast metabolism are likely just more active than others. The more active someone is, the more calories they burn, and the more likely they are to lose weight. Aerobic exercise is the most efficient way to burn calories, but any extra movement helps.

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Basal Metabolic Rate

The basal metabolic rate (BMR) is what people commonly refer to as metabolism. BMR is the rate at which someone burns energy at rest, and it can contribute to weight gain. If someone with a low BMR eats the same food as someone with a high BMR, the person with a low BMR is more likely to gain weight, even if they both get the same amount of exercise. Many things influence BMR, including genetics and body composition.

notebook explaining basal metabolic rate calculation


Weight Loss

Instead of trying to boost metabolism, there are healthier ways to achieve weight loss. Exercise is key but only when it is not used as an excuse to overeat later in the day. Building muscle may not increase metabolism, but it does lead to strong bones and muscles, making exercise easier. Other practices that help include eating only when hungry and consuming a variety of nutritious foods.

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Metabolic Disorders

Metabolic disorders occur when the metabolic process is interrupted by abnormal chemical reactions. These disorders affect the breakdown of carbohydrates, lipids, or amino acids. Some of these disorders are inherited, like Tay-Sachs disease or Hunter syndrome. Mitochondrial diseases affect the way cells produce energy. Other metabolic diseases develop over time, like diabetes. There are hundreds of inherited metabolic diseases, and treatments include everything from special diets to liver transplants.

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Prevention of Acquired Metabolic Disorders

There are many strategies to prevent an otherwise healthy person from developing a metabolic disorder over time. Daily exercise and smoking cessation are key. Diet plays a huge part, too. Doctors recommend a plant-based Mediterranean diet, DASH diet, or vegetarian diet low in saturated and trans fats and high in fiber.

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