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What is metabolism and how does it work? Key points to know

Medically reviewed on August 1, 2022 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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Metabolism: it’s a term you’ve probably come across before, whether in science class or from a health-conscious friend. And while many of us have a general sense of how our metabolism works, it’s natural to have additional questions about such a complex phenomenon.

At its core, metabolism is the chemical process behind every physical or physiological function your body undertakes, whether swimming laps at your local health club or reading this article. But what factors affect metabolism? Is there any truth to the idea that you can modulate the “speed” at which it operates?

This guide will break down the science of how metabolism works, what factors affect it, and how to determine whether yours is running in optimal condition.

What does metabolism do?

Metabolism is the chemical process your body undergoes to turn the foods and beverages you consume into energy. [1] It involves combining oxygen with the calories you acquire through diet with oxygen and releasing them into your system, which enables your body to function properly and efficiently.

Think of your metabolism as the engine that’s constantly whirring behind the scenes to supply you with the energy you need for your daily activities. Metabolic processes are also behind virtually every physiological function your body performs, including:

  • Digestion
  • Blood circulation
  • Breathing
  • Growing and repairing cells
  • Hormone regulation

Medical experts refer to the amount of energy you need for these essential body functions as your resting metabolic rate (RMR). Ultimately, this is your base-level metabolic rate.

How does metabolism work?

The term “metabolism” actually refers to two distinct, concurrent chemical processes that balance each other out:

  1. Anabolism – Also referred to as constructive metabolism, anabolism is the process of turning tiny energetic building blocks into larger complex molecules like proteins and fats. Anabolic processes include storing energy, building muscle, and healing wounds.
  2. Catabolism – Also called destructive metabolism, catabolism performs the opposite function of anabolism. During this process, larger molecules (like fats and carbohydrates) are broken down to release energy. Catabolic processes include maintaining body temperature, enabling muscle movement, and fueling anabolism.

Every time you eat or drink, the nutrients from your diet are either broken down for energy (catabolized) or stored away for later (anabolized).

While it’s crucial to store some energy for later, too much can lead you to amass body fat—one of the primary places where the body stores energy. This explains why consuming food faster than your metabolism can process may sometimes lead to weight gain.

Fast vs. slow metabolism

When people talk about their metabolism in casual settings, they often assign it a “speed.” Maybe you have a friend who says they have a fast metabolism, or you’ve heard someone on the bus complain about their slow metabolism.

People use these speeds as a way of quantifying this unseen internal process. A fast metabolism refers to an RMR that burns calories quickly, whereas a slow metabolism refers to an RMR that takes longer to expend extra calories.

Some people—especially those who are trying to lose body weight—consider having a fast metabolism to be one of the easiest ways to lose and keep off excess body fat. While individuals with “faster” metabolisms tend to burn calories faster, a slower metabolism requires fewer calories to function.

With that in mind, a faster metabolism isn’t necessarily the secret key to weight loss, though it can influence individual body weight, shape, and size. [2]

What factors affect metabolism?

While a “fast” metabolism may play a role in how your body manages energy, there are many other factors that can affect your RMR. [2]

Some of the most important ones include:

  • Genetics and hormones – There are several intrinsic and immutable factors affecting metabolism that you can’t change. For example, your sex plays a role: males typically have higher basal metabolic rate than females. [3] Age is also a factor, as metabolism tends to slow with age, largely due to loss of lean muscle mass. What’s more, some people are born with metabolic disorders that affect how they metabolize certain nutrients.
  • Diet – Anytime you eat, your metabolism kicks into overdrive. This phenomenon is called the thermic effect of food (TEF). However, not all foods are processed with equal efficiency. Your body takes longer to burn protein than carbohydrates or fats, which means your metabolism will stay active for longer when you eat a protein-rich diet. [4] So, some people do use metabolic confusion or do a metobolic reset to reach their weight goals.
  • Exercise – The more energy you expend, the more calories your metabolism must burn to keep up. As such, a high level of physical activity may serve to increase your metabolic rate.
  • Sleep – More recently, researchers have found a potential link between sleep and healthy metabolism. Studies have shown that a lack of sleep or poor sleep quality can negatively affect the hormones responsible for regulating your metabolism. [5]
  • Stress – High stress levels can also have an impact on your metabolism. In particular, cortisol (colloquially known as “the stress hormone”) is known to play a significant role in your metabolic rate. [6]

Test your metabolic health at home with Everlywell

Ultimately, your metabolism is a natural process that’s elemental to both your short- and long-term well-being, impacting your energy levels, appetite, and your weight care journey.

That’s why it’s vital to know where your metabolism stands. By taking an at-home Metabolism Test from Everlywell, you can measure three hormones known to affect metabolic health: cortisol, free testosterone, and thyroid-stimulating hormone (TSH).

With quick turnaround times, CLIA-certified lab results, and comprehensive, physician-reviewed analysis, you can start developing a better understanding of your metabolism by shopping the Everlywell at-home test kit collection today.

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  1. Metabolism and weight loss: How you burn calories. Mayo Clinic. URL. Accessed August 1, 2022.
  2. Does metabolism matter in weight loss? Harvard Medical School. URL. Accessed August 1, 2022.
  3. Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective. National Institutes of Health. URL. Accessed August 1, 2022.
  4. The truth about metabolism. Harvard Health Publishing. T URL. Accessed August 1, 2022.
  5. Sleep and Metabolism: An Overview. National Institutes of Health. URL. Accessed August 1, 2022.
  6. Interactions between sleep, stress, and metabolism: From physiological to pathological conditions. National Institutes of Health. URL. Accessed August 1, 2022.
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