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What is fast metabolism?

Sian Baker

Medically reviewed by Sian Baker, Dip ION mBANT mCNHC
on March 31, 2023. To give you technically accurate, evidence-based information, content published on the Check My Body Health blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

A fast metabolism refers to the rate at which a person’s body burns calories. People with a fast metabolism are able to burn calories quickly, which can make it easier for them to maintain a healthy weight. A fast metabolism can be caused by genetics, muscle mass, and regular physical activity.

What is the process of metabolism?

Metabolism refers to the chemical processes that occur within a living organism in order to maintain life. These processes include the conversion of food into energy (through a process called cellular respiration) and the elimination of waste products.

The process of metabolism can be broken down into two main categories: catabolism and anabolism.

Catabolism is the process of breaking down molecules to obtain energy. This process includes the breakdown of carbohydrates, fats, and proteins through a series of enzymatic reactions to yield energy in the form of ATP.

Anabolism is the process of building molecules from simpler compounds. This process includes the synthesis of proteins, nucleic acids, and complex lipids from simpler precursors.

Both catabolism and anabolism are necessary for the body to function properly, and they are constantly occurring at the same time in the body. The balance between catabolism and anabolism determines whether a person is in a state of energy balance (calories consumed equal calories expended) or energy imbalance (calories consumed do not equal calories expended).

Is it good to have a fast metabolism?

Having a fast metabolism can be beneficial for maintaining a healthy weight, as it allows the body to burn calories quickly. People with a fast metabolism may find it easier to lose weight or maintain their weight because they are able to burn more calories than people with a slower metabolism. Additionally, a fast metabolism can also lead to better muscle definition, as the body is able to burn fat more efficiently.

However, it’s worth noting that a fast metabolism alone does not guarantee a healthy weight or overall health. A balanced diet, regular physical activity, and other healthy lifestyle habits are still important for maintaining overall health and fitness.

Also, having a fast metabolism is not always desirable, people with a fast metabolism may find it difficult to gain weight or may have trouble maintaining their weight. They may have to eat more and/or more frequently than others to maintain their weight.

It’s important to remember that metabolism is a complex process that is influenced by many factors such as genetics, muscle mass, hormones, and lifestyle habits. Consult a healthcare professional if you have concerns about your metabolism.

How do you measure metabolic processes

There are several ways to measure metabolic processes in the body, including:

Calorimetry: This method measures the amount of heat produced by the body to determine the number of calories being burned.

Indirect calorimetry: This method measures the amount of oxygen and carbon dioxide the body uses to determine the number of calories being burned.

Metabolic rate testing: This method measures the amount of oxygen and carbon dioxide the body uses, as well as the volume of air the body inhales and exhales, to determine the body’s metabolic rate.

Body composition analysis: This method uses a variety of techniques such as bioelectrical impedance analysis, dual-energy X-ray absorptiometry (DXA), or skinfold measurements to determine the amount of body fat and lean muscle mass.

Biochemical tests: These tests measure the levels of various hormones, enzymes and other substances in the blood or urine that can indicate the rate of metabolism and/or the presence of metabolic disorders.

It’s worth noting that some of these methods are more invasive than others and may not be suitable for everyone. Also, these methods have limitations and might not be able to give a complete picture of the metabolic process, it’s important to consult a healthcare professional to help you interpret the results.

What causes you to have a fast metabolism?

There are several factors that can contribute to having a fast metabolism, including:

Genetics: Some people may have a genetic predisposition to a faster metabolism, meaning that their bodies naturally burn calories more quickly than others.

Muscle mass: People with more muscle mass tend to have a faster metabolism because muscle tissue burns more calories than fat tissue.

Hormones: Thyroid hormones play a key role in metabolism, and an overactive thyroid can lead to a faster metabolism.

Age: As people age, their metabolism tends to slow down, so younger people tend to have faster metabolisms than older people.

Gender: Men tend to have a faster metabolism than women, due in part to their typically greater muscle mass.

Environmental Factors: Exposure to cold temperatures, intense physical activity, stress, and certain medications can also cause a temporary increase in metabolism.

It’s worth noting that the contribution of each factor may vary from person to person. Also, there are many factors that can affect metabolism, it’s important to consult a healthcare professional if you have concerns about your metabolism.

How do you calculate a metabolic rate

There are several ways to calculate metabolic rate, but the most common method is to use the Harris-Benedict equation. This equation uses a person’s height, weight, age, and gender to estimate their basal metabolic rate (BMR), which is the number of calories the body burns at rest.

The Harris-Benedict equation for men is: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)

The Harris-Benedict equation for women is: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)

It’s worth noting that the Harris-Benedict equation is just an estimation, and it may not be accurate for everyone. There are other equations that have been developed to estimate BMR, such as the Mifflin-St. Jeor equation.

It’s also important to note that BMR is just one aspect of metabolism, and it doesn’t take into account other factors such as muscle mass, physical activity, and other environmental factors that can affect metabolism. For a more accurate assessment of metabolism, it’s best to consult with a healthcare professional and have indirect calorimetry or metabolic rate testing done.


  1. Physiology, Metabolism. StatPearls. Accessed January 12, 2020. (
  2. Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Summary. Available from:
  3. Trexler ET, Smith-Ryan AE, Norton LE. Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr. 2014 Feb 27;11(1):7. PMID: 24571926; PMCID: PMC3943438.
  4. Understanding calories. National Health Service. Accessed January 12, 2020. (
  5. Biochemistry, Heat and Calories. StatPearls. Accessed January 12, 2020. (
  6. Psota T, Chen KY. Measuring energy expenditure in clinical populations: rewards and challenges. Eur J Clin Nutr. 2013;67(5):436-442.
  7. Chung N, Park MY, Kim J, et al. Non-exercise activity thermogenesis (NEAT): a component of total daily energy expenditure. J Exerc Nutrition Biochem. 2018;22(2):23-30.
  8. Weight loss. Mayo Clinic. Accessed January 12, 2020. (
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