The part of your metabolism that burns calories throughout the day is called your basal metabolic rate (BMR).

There's little you can do to speed up your BMR to lose weight.

In order to lose weight, you must consume fewer calories than you burn each day through a combination of diet, exercise, and BMR processes that are mostly out of your control.

As you age, your metabolism will slow down but studies show that staying active can help.

This article was medically reviewed by Mir Ali, MD , bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center.

This article is part of Insider's guide on How To Lose Weight.

Metabolism is the set of chemical reactions that break down the food we eat into energy and muscle.

Though many people think that they will lose weight if they speed up their metabolism, this isn't necessarily true. Here's what you need to know about the complicated relationship between metabolism and weight-loss.

Popular myths about metabolism and weight loss

When people refer to metabolism being "fast" or "slow" what they are really referring to is a measure of Basal Metabolic Rate (BMR). BMR determines the number of passive calories that you burn — these are the calories that your body uses up while at rest.

A popular misconception is that adding muscle will help you metabolize calories faster — and while this is partially true, muscles at rest actually burn very few calories. Most of the metabolizing energy you expend is through your brain, heart, kidneys, and other organs that are constantly at work keeping you alive and healthy.

There is evidence that cardiovascular exercise can help boost your metabolism for a short period after you work out, but this effect only lasts for an hour or so and is not usually enough to cause significant weight loss.

There's also the myth that eating certain foods will speed up your metabolism. But the reality is that even if certain foods can affect your BMR it's not nearly enough to make a noticeable difference in your weight. In order to lose weight, you must create a deficit between the calories you consume through food and the calories you burn through a combination of diet, physical activity, and passive metabolic processes that are largely out of your control.

Genetics play a key role in your BMR

The sad truth is that it's hard to change your BMR in any significant way. The fact that some people naturally have a faster BMR than others is largely due to genetics.

A review, published in 2011 in Molecular Genetics and Metabolism, that examined 9 twin studies and 19 family studies found that metabolic syndrome — and some of the symptoms associated with it including obesity, high cholesterol, and insulin resistance — are common among families, suggesting a significant heritability factor.

The exception to this rule comes up only for rare illnesses like Cushing's syndrome or hypothyroidism, which both slow metabolism.

Aging and your BMR

As you age, your metabolism becomes less efficient, or what we think of as "slowing down," says Heather Seid, a registered dietician and Bionutrition Program Manager at Columbia University.

There are many reasons your metabolism slows down, including losing muscle mass and changes in your cells. But the main reason for metabolism change is that people become less active as they get older.

Unfortunately, you can't completely stop your metabolism from slowing down as you age but exercise may give you a boost. Studies show that keeping active as you grow older can help curb a metabolism slowdown.

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