What does "Metabolism" Actually Mean?

By Catherine Roy, June 30, 2023

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The term "metabolism" is often used in lay conversations and scientific debates alike. But what does metabolism actually mean? What constitutes a "slow metabolism" or a "high metabolism"? 

If those answers aren't clear, that's ok! This article dives into the science behind metabolism, how blood biomarkers can provide insight into metabolic function, and how an optimal metabolism contributes to healthspan optimization. Through science-backed recommendations to improve markers tied to metabolism, InsideTracker's personalized Action Plan can guide you to live healthier longer.

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What is metabolism?

Metabolism refers to the sum of reactions that occur in each of our cells to provide the body with energy. Metabolism is the way the body utilizes calories from food to produce the energy needed to keep all necessary bodily functions (breathing, digestion, etc) running seamlessly. The number of calories a person needs to eat throughout the day to accomplish various functions is determined, in part, by their metabolism.

Metabolism is the sum of three factors

How efficiently your metabolism functions is determined by three factors: basal metabolic rate (BMR), thermic effect of food (TEF), and energy expenditure due to physical activity (EEPA). These three pieces affect how calories are used in the body. Together, they are known as your total energy expenditure.

  • Basal metabolic rate (BMR): BMR is the total number of calories your body needs at rest—and only at rest. This means no sitting up, no talking, no use of any muscles. BMR accounts for anywhere between 60-70% of daily calorie intake, making it the largest contributor to overall metabolism. [1] We all have different BMRs because it’s determined by a number of factors including age, gender, muscle mass, hormones, stress, physical fitness level, and nutritional state. Having a fast metabolism is usually associated with a high BMR.
  • Thermic effect of food (TEF): The digestion of food involves a lot of different processes. And although you don’t have to actively work to digest a meal, your body still uses up energy doing so. The cumulative amount of calories it takes for the body to digest food makes up TEF. On average, this accounts for approximately 10% of daily energy expenditure. Protein has the greatest effect, followed by carbohydrates, then fat.
  • Energy expenditure from physical activity (EEPA): The calories your body uses during movement. This includes calories burned while working out, as well as any physical movement, like typing or folding laundry. This accounts for roughly 20% of your daily calorie burn, but can vary depending on daily activities. [1] 

So, having a fast metabolism is usually associated with a high BMR, but how about those of us with “slow” metabolisms? Is it possible to boost metabolism? According to science, yes! Here's how. 


5 biomarkers related to metabolism

There are several blood biomarkers that contribute to overall metabolism. While they aren't direct measures of total energy expenditure, they can still influence it. Let's dive into the science behind five blood biomarkers that contribute to the body's metabolic function. 

  1. Glucose: The body's primary source of energy. The body must regulate glucose levels in the blood to maintain good health.
  2. Insulin: A hormone that facilitates the movement of glucose (sugar) from the bloodstream into cells, to be used for energy or stored for later use. When this process is disrupted, it can lead to insulin resistance, a red flag for metabolic health.
  3. Cholesterol: A waxy, fat-like substance that is made in the body by the liver and serves many vital functions. Normal cholesterol levels (HDL and LDL included) are important for maintaining energy, an active metabolism, and a healthy heart and circulatory system.
  4. Triglycerides: A type of lipid found in your blood. When you eat, your body converts the calories it doesn’t immediately need into triglycerides. Then, between meals, hormones release triglycerides from storage to use for energy. Adequate levels of triglycerides are important for maintaining energy, improving metabolism, and promoting heart health.
  5. Vitamin D: An important nutrient that helps the body absorb calcium, which helps to maintain bone strength and regulate the development and maintenance of the nervous system and skeletal muscle.

These are just five of many blood biomarkers that can quantify metabolic function. Routinely measuring these markers and more can determine where your metabolism is optimal—and what still needs work. InsideTracker's comprehensive blood panel not only measures these blood biomarkers, but depending on your results, delivers personalized recommendations to improve metabolic health and several other facets of healthspan. 


How metabolism is tied to longevity

Metabolic health has evidence-based ties to longevity. The impact of metabolism on healthspan is noted through several processes in the body.  

  • The body's metabolism controls various processes that work together to maintain physiological balance and support the repair and renewal of cells, tissues, and organs. [2]
  • An efficient metabolism increases nutrient absorption, energy production, and waste removal. [3] 
  • A well-regulated metabolism helps to maintain stable blood sugar levels, control inflammation, and promote a healthy body weight. [3] 

Metabolism is critically important to monitor because metabolic dysfunction is associated with an increased risk of several chronic diseases that impact overall longevity like diabetes and heart disease. The good news is that there are science-backed ways to improve metabolism that are associated with living healthier longer. 


How to maintain a healthy metabolism

While there are many science-backed ways to maintain a healthy metabolism, here are five that InsideTracker's science team has found strong evidence to support. 

1. Prioritize sleep

It seems like a good night’s sleep is the solution for everything, and a healthy metabolism is no exception. Lack of sleep disrupts appetite hormones, increases caloric intake, and negatively alters glucose metabolism. [4, 5] Chronic, or even partial sleep deprivation, is associated with an increased risk of obesity and diabetes. [6]

To get a good night's rest, aim to get 7-9 hours of sleep every night. Developing a nighttime routine—such as powering devices down an hour before bed and reading with a cup of tea can help you get those extra hours in.

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2. Meet your daily protein goal

Compared to carbohydrates and fat, protein has the highest thermic effect, meaning the body utilizes the highest amount of calories to digest and absorb it. [7]   

Aim to include a complete protein source at every meal. For meat eaters, that can easily be done with eggs, chicken, fish, or lean beef. For plant-based eaters: tofu, tempeh, quinoa, and buckwheat are great options.

3. Add in high intensity interval training workouts (HIIT) 

HIIT workouts increase post-exercise oxygen consumption, fat oxidation, and metabolic rate. [8, 9] Essentially, they keep the body burning fuel long after your workout is over (often known as the “after-burn” phenomenon).

HIIT workouts include 30-60 seconds of high intensity aerobic work followed by 1-4 minutes of rest or recovery, repeated for 4-10 rounds. Try to incorporate HIIT workouts three times per week on nonconsecutive days. Local gym's typically have group fitness classes like HIIT.

4. Use a standing desk

Ever tried a standing desk? In multiple studies, those who used a standing desk for even just part of the work or school day had an increased energy expenditure compared to those who remained seated all day. [10, 11, 12]

Most standing desks are adjustable, meaning they can be used standing or sitting. So, if being on your feet all day seems a bit intimidating, start by alternating between sitting and standing and work your way up, literally!

5. Get more steps in 

Increasing daily step count is an effective strategy to promote physical activity throughout the day, which in turn has significant benefits on metabolic health. A 2020 systematic review found that for every 1,000-step increase in daily step count, there was an estimated 6% risk reductions in all-cause mortality. [13] 

To get more steps in throughout the day, consider going for a five-minute walk every hour. Take a spin around your neighborhood, or visit your local grocery store and walk through each aisle.



  • Metabolism describes the bodily processes needed to turn food into energy the body needs to keep it alive.
  • How many calories you need a day depends on your total energy expenditure, which is the sum of BMR, TEF, and EEPA.
  • Certain markers found in the blood can influence your total energy expenditure, such as insulin glucose, insulin, cholesterol, triglycerides, and vitamin D.
  • It is possible to boost metabolism through lifestyle factors such as quality sleep, aerobic exercise, and meeting your protein needs.


[1] https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/energy-expenditure 

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4759747/ 

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4892884/ 

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3619301/ 

[5] https://pubmed.ncbi.nlm.nih.gov/21715510/ 

[6] https://pubmed.ncbi.nlm.nih.gov/26467988/ 

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4258944/ 

[8] https://pubmed.ncbi.nlm.nih.gov/23438230/ 

[9] https://pubmed.ncbi.nlm.nih.gov/27747847/ 

[10] https://pubmed.ncbi.nlm.nih.gov/22971879/ 

[11] https://pubmed.ncbi.nlm.nih.gov/27256708/ 

[12] https://pubmed.ncbi.nlm.nih.gov/27515973/ 

[13] https://ijbnpa.biomedcentral.com/articles/10.1186/s12966-020-00978-9 

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