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What Is Metabolism? Everything You Need to Know

Researching ways to burn fat or why you might be gaining weight throughout the years? Metabolism is likely in the center of the search but its role is vital to health beyond weight loss.

What Is Metabolism? Everything You Need to Know

People have often bantered about their type of metabolism in conversation before. In a body-focused culture, it is common to spend endless hours researching how to increase metabolism in hopes of losing weight. 

Unfortunately, there are many myths surrounding metabolism. A quick search of 'how to speed up metabolism' will likely plunge you into a rabbit hole of eating more spicy food, drinking frigidly cold water, and eating every two hours, but to no avail.

It is time to clarify the vague function known as metabolism once and for all! Keep reading to discover not only how metabolism works but how to safely and sustainably maintain a high metabolic rate.

What Is Metabolism?

Most definitions of metabolism refer to it as the chemical (metabolic) processes inside cells that convert food and drink into usable energy so that the body can then carry out basic life functions. 

This is otherwise called resting metabolic rate (RMR) or basal metabolic rate (BMR). It is the minimum number of calories a body needs to complete autonomic functions like breathing, circulating blood, growing cells, and producing hormones.

The totality of metabolism includes the following and determines how many total calories one needs to maintain basic health and an appropriate weight range. As a collective, this is called total daily energy expenditure (TDEE) and includes the following:

1. Resting or basal metabolic rate - 60-70%

2. Digestion (also known as the thermic effect of food) - 10-15%

3. Physical Activity - 15-30%

4. Non-exercise thermogenic activity (NEAT) - movement that is not regimented like walking the stairs - 2-10%

How Does Metabolism Work?

First of all, the human body possesses many natural regulators of metabolism that try to keep it as close to equilibrium or homeostasis as possible. Cells are constantly receiving signs and signals that spark catalysts known as enzymes to conduct chain reactions that result in chemical byproducts such as ATP, heat, and nitrogen. The body also has built-in mechanisms that release any waste products through the skin, lungs, kidneys, and bowel. 

Ultimately, metabolism is a delicate balancing act between anabolic and catabolic activity.

Catabolic reactions aim to produce energy needed for cellular activity. Generally, this means the body is breaking down large molecules like starch and fat into ATP to then provide fuel for muscular contraction, skeletal movement, temperature and pH regulation, and anabolism.

Anabolic reactions, on the other hand, aim to build and store. Anabolism supports cellular growth and repair and storage of energy for future use. Examples of anabolic reactions include wound healing, muscular hypertrophy, and fat storage.

What Controls Metabolism?

All in all, the endocrine system regulates the rate and controls the direction of metabolism via chemical messengers known as hormones. The endocrine system is a complex web of glands and organs, including the following introduced right below. 


Located at the base of the brain, the hypothalamus stimulates and suppresses the release of hormones from the pituitary gland. It controls water balance, respiration, circadian rhythm, temperature, blood pressure, and appetite.

Pituitary Gland

A pea-sized gland that sits directly under the hypothalamus, it is often called the master gland because it secretes its own hormones and also signals other glands to produce or halt other hormones. 

Major pituitary hormones include ACTH, FSH, LH, GH, prolactin, oxytocin, ADH, and thyroid-stimulating hormone (TSH).


Also part of the digestive system, the pancreas produces insulin and glucagon, two hormones that regulate catabolism and anabolism. 

Recall that as long as insulin remains in the bloodstream, the body will remain in anabolism, This is why those with insulin resistance have such difficulty losing weight.

Testes and Ovaries

Part of the reproductive system as well, ovaries produce estrogen and progesterone and testes produce testosterone. These all affect metabolic rate.

Pineal Gland, Thymus, and Parathyroid

The pineal body, which is located in the middle of the brain, produces melatonin that regulates circadian rhythm. 

The thymus produces white blood cells that fight infections and destroy harmful cells. 

The parathyroid gland located on top of the thyroid largely regulates calcium balance and therefore, bone health.

Adrenal Gland

Located on top of each kidney, the adrenal gland works very closely with the hypothalamus and pituitary gland to release corticosteroids like cortisol, norepinephrine, and epinephrine. These all directly maintain blood pressure and regulate metabolic rate. 


A butterfly-shaped gland near the front of the neck, the thyroid is understood to have the biggest impact on metabolic rate. However, it has been mentioned that because the pituitary controls the thyroid, it should really earn silver. 

Nonetheless, the thyroid produces the master regulating hormone called thyroxine (T4) as well as triiodothyronine (T3) and thyroid-stimulating hormone (TSH). The pituitary controls the regulation of TSH, which then controls T3 production and conversion into the active thyroid hormone, T4.

What Affects Metabolism?

From genetics to diet to exercise, many variables influence metabolism. Learn how each factor does so and tips to improve on each in the new section. 


To some extent, genetics affect our metabolism. Everyone is born with a set of genes that have a propensity to be turned off or on based on the average inputs. This then affects the expression of disease or vitality amongst the body.

For example, a set of twins are both born with the exact MTHFR gene. One of the twins stayed active after college, generally eats healthfully and sleeps enough, does not smoke, and maintains meaningful relationships. Their body will essentially analyze these inputs and express the MTHFR gene in a positive or negative way. 

Because these habits are positive inputs, the MTHFR gene will likely continue correctly coding and they will maintain a reduced risk of developing health complications associated with that gene.

On the other hand, if the second twin regularly smoked, drank excessive alcohol, rarely exercised, did not sleep well or enough, and felt isolated or lonely, they would likely increase their risk of developing health problems associated with the MTHFR gene, like B-vitamin deficiencies.

If this example included two unrelated people, then one of them would have naturally inherited the ability to maintain a higher metabolism regardless of the input. This is what people are actually referring to when they discuss their high and low metabolisms. 

Indeed, this is why many smokers develop lung cancer but others die of appropriate 'old age'. The latter group possessed genes that were better equipped to respond to inflammatory stressors such as nicotine or trans fat.

Regardless, the following inputs highly affect gene expression, and therefore, metabolism much more than the literal set of genes they were born with. This can be hard to face because the responsibility falls to the individual. We cannot solely blame our genes any longer!


Of all the variables, diet likely plays the largest role in affecting metabolism. The foods we eat directly supply nutrients to cells. High-quality carbs provide fiber and antioxidants, lean protein offers helpful amino acids, and healthy fats bolster cell walls. 

These types of nutrients allow cells to keep functioning optimally. This then translates into maintaining a higher metabolism even through aging.

Conversely, eating too many inflammatory food components like saturated fat, trans fat, refined carbs, and added sugars and lower quality protein weakens cells, disrupts communication, breaks down cell walls, and more. This hurts metabolism and makes it more difficult to easily maintain a healthy weight range, especially as one ages.

Stay tuned for a very comprehensive article on how specific foods and nutrients affect metabolism!

Physical Activity & NEAT

The type, frequency, and consistent duration of exercise and non-exercise activity thermogenesis (NEAT) play a role in metabolic rate as well. 

While cardio is known for improving the cardiovascular system and boosting mood and feel-good hormones, strength training takes the cake for improving metabolism most. This is because resistance training builds muscle, and muscle tissue is the most metabolic type of tissue. 

The more muscle someone has, the more calories they will likely burn more calories at rest. Another type of exercise known as HIIT also appears to serve as a metabolism booster thanks to a phenomenon called exercise post-oxygen consumption (EPOC), which also increases caloric burn for plenty of hours after exercise is concluded.

The fourth type of movement - NEAT - may also affect metabolism, but to a lesser extent than consistent exercise. NEAT is considered any extra movement outside of regimented exercise and includes activities like walking upstairs, doing household chores, short walks, gardening, chasing kids, etc. 

However, if someone is not regularly engaging in planned exercise, then NEAT becomes much more important. While NEAT is meant to be somewhat effortless, some people may meaningfully boost their metabolism by aiming to get in 30-60 minutes of NEAT every day. 

Muscle Mass

Piggybacking off the previous section, lean body mass plays a large role in metabolism. Regardless of exercise, the amount of muscle tissue one has greatly determines metabolic rate. Lean muscle tissue is the most metabolic tissue, so the more one has, the higher their metabolism. 

So, the person that completes three to four 45 min strength training sessions per week could very well have a better metabolic rate than the person doing one to two-hour cardio sessions almost every day. More exercise does not always equate to more positive metabolic function. Smart, evidence-based workout programs that do not stress the body out too much achieve positive metabolic adaptations much better.


Drinking unbearably cold water will not raise metabolism in any meaningful amount long term. But hydrating enough will make it easier for metabolism to remain high. Water lubricates cells and ensures they have enough 'life force' to continue doing their jobs.

On the other hand, dehydrated cells tend to be sluggish and will not be able to perform as efficiently. In other words, dehydrated cells work slower and this translates into a slower metabolism.


Finally, the variable few people want to acknowledge as being important towards metabolism– sleep. But it simply cannot be denied that getting enough high-quality sleep improves metabolism a meaningful amount. 

Cellular growth and repair occur during those precious night hours, so chronically undersleeping does not allow enough time for cellular recovery. This causes cells to break down and decrease their ability to withstand stress. 

A common theme, the result is dull, lethargic cells. Not to mention, undersleeping affects hormones that regulate important metabolic functions like appetite and blood sugar management. 

How to Boost Metabolism

In theory, the simplest way to boost metabolism is to optimize the above lifestyle habits. Because metabolism is regulated by an entire system, boosting it requires optimizing each and every part.

It should also be said that boosting metabolism is very individualized. One person might respond better to dietary factors while another sees significant improvement with exercise and hydration variables. Nonetheless, here is a good starting point for everyone. They might not seem fancy, but they are surely effective.

Metabolic Variable

How to Optimize


Make the majority of carb sources antioxidant-rich: fiber, whole grains, fruits, and vegetables and reduce processed/packaged foods to <1-2/day

Eat enough protein to facilitate muscle growth/maintenance (.8-2.0 g/kg body weight dependent on goals)

Include plenty of healthy fat sources and reduce inflammatory ones: omega-3 fatty acids in fatty fish, olive oil, avocados, nuts and seeds


Exercise consistently (3-6x/week)

Include strength training of all major muscle groups 2-3x/week

Prioritize muscle recovery and avoid over-exercising, which can increase stress hormones and slow metabolism

Muscle Mass

Include strength training with progressive overload principles

Consume enough high quality/bioavailable protein like grass-fed beef, wild-caught fish, free-range eggs, and beans and legumes

Optimize NEAT for additional benefits


Aim to drink at least ½ body weight in ounces of water daily

Make most beverage choices hydrating


Consistently get 7-9 hours of high-quality sleep

Avoid screens and/or use blue light blocker glasses 2-3 hours before bed

Other Potentially Effective Tips

Take 1-5 min (very!) cold showers to increase brown fat (Wim Hof method)

Include spicy food sometimes (no need to go overboard)

Consume 60-100 mg caffeine per day (at least 8 hours before bedtime) as desired 

Exercise outdoors

Get 10-15 min of sunshine without sunscreen (to optimize vitamin D)

Manage stress effectively to reduce stress hormones

Maintain meaningful relationships/connections

Metabolism Recap

Metabolism is complex and influenced by many unique factors such as genetics and diet. Overall, though, metabolism is not necessarily fixed and can be improved for the better.

Adopting a healthy lifestyle, including eating a balanced diet and increasing activity levels, can support an efficient metabolism. Other factors, like taking cold showers and managing stress, may also be helpful metabolism boosters. 


Anatomy of the Endocrine System. Johns Hopkins Medicine. https://www.hopkinsmedicine.org/health/wellness-and-prevention/anatomy-of-the-endocrine-system

Metabolism (for Teens). KidsHealth. The Nemours Foundation. Reviewed July 2019. https://kidshealth.org/en/teens/metabolism.html.

Overview of Metabolism. Khan Academy. https://www.khanacademy.org/science/ap-biology/cellular-energetics/cellular-energy/a/overview-of-metabolism.