What Is Metabolism?

When it comes to losing weight or maintaining your current weight, your metabolism can influence your results. If you're concerned about this, it's helpful to understand exactly what metabolism is. It's also beneficial to know what can affect it and, if yours might be slower, how to help speed it up.

Metabolism Defined

Metabolism refers to the biochemical processes that the body uses when converting food (calories) into energy to both sustain life and to support physical activity, whether exercise or non-exercise. These processes include:

• Breathing
• Digesting food
• Delivery of nutrients to your cells through the blood
• Use of energy by your muscles, nerves, and cells
• Elimination of waste products from your body 

The rate at which you burn calories or energy is called your metabolic rate. This number includes your basal metabolic rate (BMR)—the number of calories needed to support essential functions, like breathing and circulating blood—and calories burned during physical activity.

Factors Affecting Metabolism

Everyone's metabolic rate is different, as many factors can influence how fast (or slow) our body uses or converts energy.

Age

Metabolism slows as we age. Some studies suggest that this is because our body composition changes as we get older. We gradually lose fat-free mass and, since fat burns fewer calories than muscle, our metabolism declines. Age-related changes in our organs can also reduce metabolic rate.

Sex

Males generally have a higher metabolism than females. Research indicates that this could be due to females conserving energy and storing fat more efficiently than their male counterparts, though it also appears that differences in various hormones may play a role as well.

Body Composition

Lean muscle mass burns more calories than fat, even when your body is at rest. So, the more muscle you have, the more calories you burn over the course of a day and the higher your metabolism. For people who are obese, energy expenditure can be impacted by inflammation.

Body Size (Height)

Your height can also affect your body's metabolic rate, but in somewhat complex ways. People who are taller tend to have a higher BMR (because they're bigger), but some research has found that they tend to burn less calories during exercise, relative to their body weight, compared to shorter people.

When both your height and waist measurements are taken into consideration, it can help determine whether you're at risk of developing metabolic abnormalities such as metabolic syndrome.

Body Temperature

The body uses as much as 40% of its total energy expenditure in an attempt to keep its temperature stable. Therefore, if you are exposed to extreme temps, your body will have to work harder. Working harder raises your metabolism.

Caffeine or Stimulant Intake

If you've ever had too much coffee or too many energy drinks, you have likely felt your metabolism raise firsthand. This is because stimulants such as caffeine can increase your metabolic rate. Their risks can outweigh their benefits, though, so this isn't the safest way to boost your metabolism.

Hormones

If thyroid hormones are not produced properly by your body, your metabolism may increase or decrease. If the thyroid doesn't produce enough hormones (hypothyroidism), the metabolism slows, which may result in weight gain. Whereas, if the thyroid produces too much (hyperthyroidism), this typically contributes to weight loss.

Pregnancy

Women who are pregnant have a faster metabolism. This is due to an increase in body mass, as well as physiological changes in the body. If the woman starts out with a low body weight, her food intake may have to be increased to ensure that she gets enough calories and nutrients.

Food Intake

What's one of the first things most people do when they go on a diet? They cut calories and reduce their food intake. However, your body needs the nutrients in food to support a healthy metabolism. Metabolism also increases when food is being digested.

Activity Level

When you move more during the day, either through exercise or routine daily movements like walking or standing, your body burns more calories. The activity revs up your metabolism, making it easier to lose weight or maintain a weight loss.

Calculating Your Metabolic Rate

To determine your current metabolic rate, you first need to calculate your BMR, or the number of calories your body needs for basic functioning. The most accurate way to do this is to have it tested in a lab. Some health clubs offer metabolic testing as well (for a fee).

Another option is to calculate your estimated BMR yourself. Online calculators are available or, if you'd prefer to calculate this number by hand, you can do so by using the Harris-Benedict Equation:

• Men:  88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years) = BMR
• Women: 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years) = BMR

Once you have your BMR, you can figure out your total metabolic rate. This number is a combination of your BMR and the calories used for processes like exercise and other daily movements. 

Using a fitness tracker is the easiest way to add up the number of calories burned due to movement. If you burn 700 calories from daily movement, for example, and your basal metabolic rate is 1200 calories, your total energy consumption (metabolic rate) would be about 1900 calories.

How to Increase Metabolism for Weight Loss

There are some things that you cannot change about your metabolism. For example, you can't change your age or sex. But there are some things that you can do to boost your metabolism and lose weight. These include:

• Exercise: You burn more calories when you exercise. Even an easy workout increases your metabolism. Harder and more intense workouts burn more calories.
• Increase your daily movement: No time to exercise? Move more during the day. Simple daily tasks like walking, climbing stairs, gardening, and housework require your body to work harder and burn more calories.
• Add muscle: You can improve your body composition to burn more calories. Do strength training exercises to build muscle, and you can burn more calories all day long, even when your body is resting. 
• Eat the right number of calories: Eating too many calories can cause weight gain. Eating too few calories can cause your metabolism to slow down. Make sure you're eating enough calories to maintain a healthy metabolism.

A Word From Verywell

Your metabolism will change slightly from day to day. If you can learn how to manage and maintain a healthy metabolism on a regular basis, it can be easier to achieve both weight loss and weight maintenance for the long term.