What Is Metabolism?

woman walking with yoga mat

Jordan Siemens / Getty Images

Your metabolism is unique to you, and the rate of your metabolism depends on many factors. Some people believe their metabolism is fast or slow and often attribute their body weight to their metabolic rate.

While metabolism does play a role in body weight, it isn't set in stone and is only one aspect of how you burn calories or balance energy levels. Learn more about what metabolism is, how it can change, and tips on maintaining a healthy metabolic rate.

What is Metabolism?

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

Metabolic Processes

  • 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 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.

The rate at which you burn calories or energy is called your metabolic rate. Your BMR is the most significant component of your metabolic rate, accounting for 60% to 75% of your total calories expended daily.

Factors That Affect Metabolism

Everyone's metabolic rate is different, as many factors can influence how fast (or slow) our body uses or converts energy. These factors include your age, sex, body composition and size, whether you are pregnant, eating enough, and more. Read more about these factors below.

Age

Metabolism slows as you age. Some studies suggest that this is because your body composition often changes as you get older. You may gradually lose lean mass while your body fat levels may stay the same or increase. Since fat burns fewer calories than muscle, your metabolism may decline.

This loss of lean mass leads to body composition changes, which are a factor regardless of age. However, age-related muscle decline, called sarcopenia, is a known health risk that does contribute to increased visceral and adipose tissues that can cause health problems.

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.

However, one reason males may tend to have a higher metabolism is due to their propensity to carry more lean mass, which is metabolically active and increases the metabolic rate. Therefore, this factor may be primarily due to body composition, rather than sex.

Women's total energy expenditure when unadjusted for fat-free mass is on average about 5% to 10% lower than men's, which is partly due to sex differences in body composition.

For women, in particular, menopause signifies a shift in hormones that also changes metabolism. After menopause women become more insulin resistant and have decreased levels of estrogens and increased levels of circulating androgens. These hormonal changes can alter the metabolism.

Body Composition

Lean muscle mass burns more calories than adipose tissue, 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. Lean mass is also more insulin sensitive and offers protective effects against metabolic disease.

For people who are obese, energy expenditure can be impacted by inflammation.As well, high body fat mass lowers the amount of glucose and fatty acids the metabolism uses as fuel. Increasing lean mass has been shown to reduce this effect and improve metabolism.

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 fewer calories while walking relative to their body weight, compared to shorter people. This is due to more efficient walking by taking longer strides.

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.

People who are obese tend to have lower core temps, so some researchers suggest that this could have lowered their metabolism and contributed to their initial weight gain.More research is necessary.

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. Caffeine increases your metabolic rate significantly during ingestion and continues for three hours.

During exercise, caffeine boosts the rate of fat burning that occurs due to increased metabolic rate. This effect remains for several hours after exercise.

Hormones

Your metabolism may increase or decrease if your body does not appropriately produce thyroid hormones. 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.

The aforementioned hormonal differences between males and females also come into play, along with the shifts in hormones during and after menopause. These hormones affect glucose, amino acid, and protein metabolism and the metabolization of nutritional fats, and the distribution of fat on the body, such as hips, thighs, and abdomen.

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

People often cut calories and reduce their food intake when trying to lose weight. However, your body needs the nutrients in food to support a healthy metabolism. Metabolism also increases when food is being digested. This is called the thermic effect of food.

The thermic effect of food (TEF) is the number of calories your metabolism burns to digest your food, and it differs based on which foods you eat. This contributes to your non-exercise activity thermogenesis (NEAT), which makes up your total energy expenditure.

Your personal TEF can be different depending on several factors. For instance, TEF slows as you age, which is another reason why age contributes to changes in metabolism.

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.

Your total energy expenditure can change from day to day depending on activity level, but your basal metabolic rate stays fairly steady.

Your total daily energy expenditure (TDEE) includes all the calories you burn during a 24-hour period. Calories burned come from processes including your brain functions, breathing, digestion, and other bodily functions for living. It also comes from your physical activity of any kind like fidgeting or intentional exercise.

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 determine your total metabolic rate. This number combines 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, your total energy consumption (metabolic rate) would be about 1900 calories.

How to Increase Metabolism for Balanced Weight

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 support a balanced weight. These include:

Exercise and Daily Movement

You burn more calories when you exercise. Energy used to exercise is called exercise activity thermogenesis (EAT), which refers to intentional exercise activity. Unintentional physical activity and movements are called non-exercise activity thermogenesis (NEAT). EAT contributes about 5% of TDEE and NEAT makes up 15% or more of TDEE on average.

Increasing your NEAT can really add up, so try things like a treadmill desk, pacing during phone calls, playing with the kids or dog, or doing chores around the house. Simple daily tasks like walking, climbing stairs, gardening, and housework require your body to work harder and burn more calories.

Build Muscle

You can improve your body composition to burn more calories. Losing weight can help, but adding lean muscle mass is even more advantageous. Do strength training exercises to build muscle, and you can burn more calories all day long, even when your body is resting. 

Eat the Correct Amount 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.

Research shows that consuming a calorie deficit that is too large or prolonged can decrease your metabolic rate, making weight loss more challenging. A smaller, sustainable calorie deficit that is broken up with diet breaks is less likely to cause diet fatigue both physically and mentally.

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 regularly, it can be easier to achieve weight loss and weight maintenance for the long term. Speaking to your health care provider about your weight loss goals and concerns is wise.

24 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. National Library of Medicine. Metabolism.

  2. Comana F. Resting metabolic rate: How to calculate and improve yours. National Academy of Sports Medicine.

  3. Geisler C, Braun W, Pourhassan M, et al. Age-dependent changes in resting energy expenditure (REE): Insights from detailed body composition analysis in normal and overweight healthy Caucasians. Nutrients. 2016;8(6):322. doi:10.3390/nu8060322

  4. Galmes-Panades AM, Konieczna J, Abete I, et al. Lifestyle factors and visceral adipose tissue: Results from the PREDIMED-PLUS study. Luque RM, ed. PLoS ONE. 2019;14(1):e0210726. doi:10.1371/journal.pone.0210726

  5. Mauvais-Jarvis F. Sex differences in metabolic homeostasis, diabetes, and obesity. Biol Sex Differ. 2015;6(1):14. doi:10.1186/s13293-015-0033-y

  6. Yoo J, Fu Q. Impact of sex and age on metabolism, sympathetic activity, and hypertension. FASEB j. 2020;34(9):11337-11346. doi:10.1096/fj.202001006RR

  7. Patni R, Mahajan A. The metabolic syndrome and menopause. J Mid-life Health. 2018;9(3):111. doi:10.4103%2F0976-7800.241951

  8. McCarthy D, Berg A. Weight loss strategies and the risk of skeletal muscle mass loss. Nutrients. 2021;13(7):2473. doi:10.3390/nu13072473

  9. Shan B, Wang X, Wu Y, et al. The metabolic ER stress sensor IRE1a suppresses alternative activation of macrophanges and impairs energy expenditure in obesity. Nat Immunol. 2017;18:519-29. doi:10.1038/ni.3709

  10. McPherron AC, Guo T, Bond ND, Gavrilova O. Increasing muscle mass to improve metabolism. Adipocyte. 2013;2(2):92-98.

  11. Weyand PG, Smith BR, Schultz NS, Ludlow LW, Puyau MR, Butte NF. Predicting metabolic rate across walking speed: one fit for all body sizes? Journal of Applied Physiology. 2013;115(9):1332-1342. doi:10.1152/japplphysiol.01333.2012

  12. Liu L, Ping Z, Li L, Yang Y, Li C, Zhang M. [Power and the cutoff value of waist-to-height ration predicting metabolism syndrome]. J Hygiene Res. 2012;41(6):992-6.

  13. Landsberg L. Core temperature: A forgotten variable in energy expenditure and obesity? Obesity Rev. 2012;13(S2):97-104. doi:10.1111/j.1467-789X.2012.01040.x

  14. Liu A, Arceneaux III K, Chu J, et al. The effect of caffeine and albuterol on body composition and metabolic rate. Obesity. 2015;23(9):1930-5. doi:10.1002/oby.21163

  15. Acheson KJ, Zahorska-Markiewicz B, Pittet P, Anantharaman K, Jéquier E. Caffeine and coffee: Their influence on metabolic rate and substrate utilization in normal weight and obese individualsAm J Clin Nutr. 1980;33(5):989-97. doi:10.1093/ajcn/33.5.989

  16. Gutiérrez-Hellín J, Del Coso J. Effects of p-synephrine and caffeine ingestion on substrate oxidation during exerciseMed Sci Sports Exerc. 2018;50(9):1899-1906. doi:10.1249/MSS.0000000000001653

  17. Kawicka A, Regulska-Ilow B. Metabolic disorders and nutritional status in autoimmune thyroid disease. Postepy Hig Med Dows (Online). 2015;69:80-90. doi:10.5604/17322693.1136383

  18. Comitato R, Saba A, Turrini A, Arganini C, Virgili F. Sex hormones and macronutrient metabolism. Critical Reviews in Food Science and Nutrition. 2015;55(2):227-241. doi:10.1080%2F10408398.2011.651177

  19. Most J, Dervis S, Haman F, Adamo K, Redman L. Energy intake requirements in pregnancy. Nutrients. 2019;11(8):1812. doi:10.3390/nu11081812

  20. Kullman S, Kleinridders A, Small D, et al. Central nervous pathways of insulin action in the control of metabolism and food intake. The Lancet: Diabetes & Endocrinology. 2020;8(6):524-34. doi:10.1016/S2213-8587(20)30113-3

  21. Calcagno M, Kahleova H, Alwarith J, et al. The thermic effect of food: A reviewJ Am Coll Nutr. 2019;38(6):547-551. doi:10.1080/07315724.2018.1552544

  22. Du S, Rajjo T, Santosa S, Jensen MD. The thermic effect of food is reduced in older adultsHorm Metab Res. 2014;46(5):365-9. doi:10.1055/s-0033-1357205

  23. Bosy-Westphal A, Hägele FA, Müller MJ. What is the impact of energy expenditure on energy intake? Nutrients. 2021;13(10):3508. doi:10.3390/nu13103508

  24. Casanova N, Beaulieu K, Finlayson G, Hopkins M. Metabolic adaptations during negative energy balance and their potential impact on appetite and food intake. Proc Nutr Soc. 2019;78(3):279-289.

Additional Reading
  • U.S. National Library of Medicine. Metabolism. Updated July 2, 2020.