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What is fast metabolism?

Medically reviewed by Neka Miller, PhD on January 12, 2020. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Wondering what a fast metabolism actually is how you can determine if you have one? Then read on to discover the basics of “fast metabolism.”

But first, to better describe what fast metabolism is, let’s clarify what metabolism itself is.

Check your levels of three key hormones that affect metabolism and weight (cortisol, testosterone, and thyroid-stimulating hormone or TSH) with the easy-to-use, at-home Metabolism Test. Note that this test does not give you a measurement of your metabolic rate.


Understanding the process of metabolism

Metabolism describes the tightly-regulated biochemical process the body uses to convert the food you consume into the energy needed to power your body’s many activities—including crucial functions related to growth, movement, and reproduction.

A couple of key concepts around metabolism include the following:

  • Catabolism is when large molecules are broken down into smaller molecules during metabolic processes. This often involves the release of energy.

  • Anabolism occurs when smaller molecules are reformed into more complex molecules that the body needs. Unlike catabolism, anabolism uses energy to build larger molecules.

Another key part in the process of metabolism are hormones like cortisol, testosterone, and thyroid-stimulating hormone (TSH)—all of which play key roles in supporting metabolic functions and activities. When your body experiences changes in the hormones that regulate metabolism, your energy levels, weight, and body composition may change.

What does it mean to have a fast metabolism?

When people talk about having a “fast metabolism,” this means that one’s metabolic processes consistently burn up more calories in a given time frame compared to the average for some population or set of people. Calories are a unit of measure that represents the amount of energy in food and drinks; in popular usage, “calories” are the same as the more technical term “kilocalories.”

What is high metabolism?

A “high metabolism” is just another way to refer to a fast metabolism—meaning your body tends to burn more calories in a given timeframe (even when at rest) relative to the metabolism of other people you’re using as a point of comparison.

Experiencing changes in your weight or energy levels and aren’t sure why? The Everlywell at-home Metabolism Test lets you check 3 key hormones commonly associated with metabolism and weight to help narrow down possible causes and determine whether a hormone imbalance may be affecting your metabolism. Note that this test does not give you a measurement of your metabolic rate.

Measuring metabolic processes

There are several different ways to measure, or quantify, key aspects of metabolism. Fundamentally, these measurements aim to provide a better understanding of one’s energy intake and usage—in other words, one’s energy balance.

Here are some important ways metabolic processes can be measured:

Basal metabolic rate (BMR): The daily rate at which your body uses energy while at rest (the basal level) to power only your vital functions (think breathing and maintaining your body temperature). It involves a lot of different systems in the body. It’s estimated that about 60-80% of the body’s total energy expenditure is due to BMR. Accurately determining one’s BMR can be challenging and requires specialized instruments (such as calorimeters). But it’s possible to calculate an estimated BMR with these equations:

  • Women: BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)
  • Men: BMR = 66 + (6.23 x weight in pounds) + (12.7 x height in inches) - (6.8 x age in years)

For adult females, a BMR of 1300-1500 calories per day is average; for adult males, the average BMR is 1600-1800 calories per day.

Thermic effect of feeding (TEF): Calories burned during digestion and while your body is processing food. TEF accounts for about 10% of the body’s total energy expenditure.

Thermic effect of exercise (TEE): The amount of calories that are expended to support physical activity. This includes physical activities intentionally undertaken as part of an exercise regimen or sport as well as non-exercise activity thermogenesis (NEAT), which includes activities like fidgeting, changing one’s posture, standing, walking around, and cleaning.

What causes you to have a fast metabolism?

Your metabolism is largely influenced by genetics. However, other factors may contribute to how well and how quickly your metabolic processes burn through calories, including:

  • Sex
  • Age
  • Muscle mass
  • Body size and composition
  • Physical activity levels
  • Hormone disorders (for example, Cushing’s syndrome and hypothyroidism)

Additionally, people with more lean muscle mass are known to generally have a faster metabolism because they are able to burn more calories while in a state of rest. Muscle cells require more energy than fat while at rest, which means that more lean muscle mass can lead to an increased metabolic rate (and therefore more calories are burned more frequently).

(Related content: Signs of fast metabolism)

Learn your levels of 3 key hormones (cortisol, testosterone levels, and thyroid-stimulating hormone or TSH) that affect metabolism and weight with the Everlywell at-home Metabolism Test. This at-home lab test lets you easily collect your sample from the comfort of your home, send it to a CLIA-certified lab for testing using the prepaid mailer provided in the kit, and get digital results in just a few days. The test can help indicate if a hormone imbalance may be interfering with your weight gain or weight loss goals. Note that this test does not give you a measurement of your metabolic rate.

Signs of a slow metabolism

Wondering how to speed up metabolism? Here’s what to know


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