When we hear the word metabolism, many of us instinctively think about our weight and what we can and cannot eat or how having a “slow” or “fast” metabolism affects our nutrition. Metabolism, however, is much more nuanced than most people realize. It not only refers to the way our body regulates our weight but also includes all of the chemical processes within our bodies that help to maintain normal function. Let’s take a deeper dive into the question “what is metabolism?” and discover how it is influenced by our food choices and genes, to help us better understand how to live a healthier life.
What Is Metabolism?
Metabolism is how your body converts food into fuel to power your body. It also includes the synthesis of molecules such as DNA, RNA, proteins, lipids, and certain carbohydrates and the removal of certain waste products. However, this definition is deceptively simple for a system that is so complex and essential to our everyday survival.
Our body’s metabolic process is an intricate network that involves the brain, stomach, heart, pancreas, kidney, brown fat, white fat, beige fat, and many more tissue types.1 Because metabolism is such a complex and fascinating topic, our goal is to simplify all confusion surrounding the all-important question “what is metabolism?”
What Is Metabolism in Relation to Nutrition?
Good nutrition is a crucial component of maintaining a healthy metabolism. Essential nutrients supply energy—or calories—and give our bodies the necessary chemicals we cannot synthesize ourselves. The foods we eat provide a variety of substances that are vital to the building, repair, and upkeep of our bodily tissues. After all, what is metabolism without efficiently functioning systems?
In order to supply this energy, our digestive system releases enzymes that break down proteins, fats, and carbs into their smaller molecules. These molecules—which include fatty acids, amino acids, and sugars—can be carried throughout the body to cells for fuel. When we consume more energy than we need, these molecules are stored for later use in adipose (fat) cells, the liver, or the muscles.
The process of using energy stores within the body, or building new healthy tissue, is called anabolism. Releasing fuel from our energy reserves, or breaking down tissue, is called catabolism. To fully understand what metabolism is, let’s explore these terms a bit more.
Anabolism is the process in which our bodies synthesize large molecules out of smaller ones. Anabolism maintains the health of our tissues. When anabolic reactions take place in the body, they use simple molecules and chemicals to manufacture many different complex products. These include the growth and mineralization of our bones, as well as increases in muscle mass.
The body uses metabolism hormones to manage energy stores and optimize nutrient intake.
Here are some examples of anabolic hormones:
- Growth hormone is made by the pituitary gland, which stimulates growth.
- Insulin is made by the pancreas and regulates the level of sugar glucose in our blood supply to make sure it doesn’t get too high. It’s worth noting that human cells cannot utilize glucose without proper insulin.
- Testosterone helps develop male sex characteristics, such as facial hair and a deeper voice. It also holds the job of strengthening bones and muscles.
- Estrogen is involved in strengthening our bone mass and also helps women develop female characteristics, like breast growth.
Catabolism is the process in which our bodies release energy by breaking down larger molecules into simpler components. For instance, when the body needs to increase its glucose levels, it releases the hormone glucagon and signals to the liver that it’s time to release the stored glucose (which is in the form of glycogen) into the bloodstream. This is a process known as glycolysis and is a prime example of catabolism.
Here are some examples of how catabolic hormones work:
- Adrenaline, also known as the fight-or-flight hormone, is released from the adrenal glands during times of extreme stress or danger. It is largely responsible for the body’s immediate response to a crisis.
- Cortisol, commonly known as the stress hormone, is a steroid hormone that helps regulate body functions in times of high stress. It puts nonessential processes—such as immunity and reproduction—on hold and maintains crucial processes like blood pressure.
- Glucagon is a hormone that works with the body to control glucose levels by signaling to the body when glucose needs to be released by the liver. It works opposite insulin to make sure blood sugar levels don’t drop too low.
In order to reap the full benefits of having an informed answer to the question “what is metabolism?” you will need to understand how metabolic processes work within the body. An individual’s diet needs to contain not only essential macronutrients—such as proteins, fats, and carbohydrates—to maintain a healthy metabolism, but also key micronutrients—such as iron and vitamins B and D. Adequate hydration also plays a key role in healthy metabolic functions.
Learning Facts and Debunking Myths About Metabolism
Being able to tell the difference between metabolism facts and myths will help you know which nutrition experts to listen to and which ones to tune out. Here are some common truths and misconceptions about metabolism.
Fact: Metabolism occurs in every cell.
That is true. Metabolism is the sum of reactions that occur within our bodies.
Fact: The majority of the calories you burn are due to your basal metabolic rate (BMR).
Indeed. As opposed to energy burned through any movement or activity, BMR is the energy needed simply to keep us alive.
Fact: Individuals vary in metabolic rates.
Yes, there is actually a lot of variation between individuals when it comes to metabolic rates. Many factors go into solving the question “what is metabolism?” that may also influence why two people can eat the same number of calories with incredibly different results or outcomes.
Fact: Your metabolism decreases as you age.
This is technically correct. Our muscle mass decreases as we age, which contributes to a slower metabolic rate. However, while weight gain is often associated with growing older, it isn’t usually a direct result of your metabolism slowing down but rather the fact that most of us become significantly less active as we age.
Myth: Eating several smaller meals throughout your day increases your metabolism.
While eating smaller meals may fit well into some people’s lifestyles, the research overall does not support the notion that eating frequently throughout the day increases the number of calories we burn or helps with fat loss. In fact, for some individuals, frequent meals can actually cause them to feel hungrier during the day and lead to overconsuming food.
Myth: Skipping meals is a smart way to lose weight fast.
You may lose weight by eating less food, but you’re not helping your metabolism out in a healthy way. In fact, when you are not eating enough for long periods of time, your body goes into starvation mode. Your metabolism slows in hopes that you’ll use up less energy and burn fewer calories. Skipping meals will likely leave you feeling even hungrier and craving (potentially unhealthy) foods, which can result in eating more calories than your body needs.
What Factors Influence Your Metabolism?
As we previously mentioned, there are many things that affect your metabolism. Let’s explore the factors that work together to influence your metabolism every day.
Genes and Your Metabolism
Over 400 different genes have been connected with obesity—although only a few of them appear to be major contributors. Genes can play a role in an individual’s appetite, sense of fullness, cravings, metabolism, distribution of body fat, and even the tendency to eat as a mechanism to cope with stress or sadness. Research has suggested that genes may account for 25 to 80 percent of a person’s risk of obesity.
No two people are the same. Each of us has our very own, highly unique genetic makeup. To address weight issues, you may find it beneficial to understand the significant role genes play in excess weight. Genes give our bodies instructions on how to respond to changes in the environment.
A variation in how different people respond to the same environment tells us that genes play a role in weight. Studies of the fat mass and obesity-associated (FTO) gene show that its most common genetic variants are strongly associated with the occurrence of type 2 diabetes and cases of obesity.2
How Nutrition and Dietary Intake Impact Metabolism
Many modern diets, such as the standard American diet (SAD), are low in nutrient diversity and high in energy-dense foods. Energy-dense foods are often foods that are high in fat but have low water content. Diets like SAD, which are full of processed and high-sugar foods, are associated with metabolic syndrome.3 The human diet is meant to include a diversity of components, including nutrients that supply the raw materials we need to fuel multiple metabolic processes in every cell.
For healthy weight maintenance, our energy intake needs to match our energy expenditure and our macronutrient intake has to balance the body’s macronutrient oxidation as well.4 So, what is metabolism, really? Ideally, it is a true equilibrium between the energy we consume and the energy we expend.
Studies have shown that reaching this balanced state is easier when we eat plenty of whole grains, fruit, vegetables, and lean proteins—all of which help our bodies power their functions and activities.5
Additionally, metabolism is much more than just our weight. Focusing on meeting your nutritional needs over lowering the number on a scale helps to build more sustainable eating behaviors that are linked to good health. Vitamins, fiber, minerals, and other nutrients are very important to long-term well-being. When people pay more attention to losing weight, they may end up becoming deficient in vital nutrients, such as calcium or vitamin B12. Again, it’s not about cutting out entire food groups but ensuring balanced meals.
Metabolism of Macronutrients
When you restrict your food supply, a number of circulating peptides, substrates, and hormones act on your hypothalamus, brain stem, and autonomic nervous system to increase your appetite in an effort to correct the macronutrient balance.4
Since energy is needed to properly fuel metabolic processes in our systems, it can be quite handy to have a way to calculate your energy needs. When wondering “what is metabolism?” an equally crucial question to ask yourself is “how many calories do adults need?” Or, more specifically, how many do YOU need?
Knowing your personal daily calorie intake needs can be a great first step in adopting a realistic eating plan. When supplemented with a physical activity plan, you can attain—and maintain—your healthiest weight. To interpret your BMI with a calculator tool, you can use these numbers as a guideline: a healthy BMI is between 18.5 and 24.9 kg/m², overweight is between 25 and 29.9 kg/m², and obese is 30 kg/m² or more.
What Is Metabolism in Relation to Weight?
Factors that contribute to the regulation of our metabolism include sex, age, physical activity level, and body composition. Our metabolic functions are also influenced by hormones, such as those produced by the thyroid gland and pancreas. Additionally, certain health conditions or health statuses can impact metabolism, including some diseases and injuries.
The body’s total energy expenditure (TEE) can be further divided into four various areas known as our basal metabolic rate (BMR), resting metabolic rate (RMR), thermic effect of food (TEF), and physical activity.
Basal Metabolic Rate and Resting Metabolic Rate
BMR and RMR are often used interchangeably, but they have slightly different definitions. Your BMR is simply the minimum number of calories that your body needs to carry out all basic functions and maintain life.
Your RMR is the number of calories that your body burns while it’s resting. BMR measurements are slightly more accurate, while RMR measurements are taken in less strict conditions. These basic resting rates account for most of the energy you expend on a daily basis.
Thermic Effect of Food
TEF, also known as thermogenesis, is the amount of energy the body needs to digest the foods and drinks consumed throughout the day and absorb, transport, and store nutrients. Thermogenesis accounts for about five to ten percent of your energy use.
The energy used by physical activity is drastically varied between individuals. Physical activity is not only how much exercise we get each day, but all of a person’s movement—including unintentional activities like shivering, fidgeting, or cooking dinner. Physical activity accounts for the last ten to 15 percent of the energy that we burn each day.
Note that your current weight can actually affect your metabolism. Weight loss—especially extreme weight loss—is more complicated than simply eating and drinking fewer calories than you burn.
Up to 90 percent of people who have lost a significant amount of weight will inevitably gain it back.6 Sustainable weight management can be difficult since our bodies, believe it or not, are programmed to be resistant to weight loss. This is due to factors like hunger hormones, including leptin and ghrelin.
The theory is that your body has a set point largely controlled by your genes and extracellular fluid that it will keep trying to get back to.7 In order to overcome weight loss-induced counter-regulation when you’re overweight, biological signals must be taken into account.
This also helps to explain people’s age-old frustration with weight loss plateaus. As pounds are shed, you lose both muscle and fat. Muscle is what aids us in keeping our metabolism up, so as you lose weight, your metabolism declines and you burn fewer calories than you were burning at your heavier weight.
What Is Metabolism in Relation to Exercise?
Your overall fitness level has an effect on your metabolism, too. One study compared the effects of resistance training, aerobic training, and combined aerobic and resistance training on blood lipids, anthropometric parameters, and cardiorespiratory fitness in obese or overweight individuals.8
Evidence highlights combined aerobic and resistance training as the most effective approach to controlling weight and improving certain measures, such as waist circumference. Therefore, a combination of training is likely valuable in a recommended prevention and treatment plan for those at an unhealthy weight. Incorporating resistance training into your regular exercise routine is also helpful for maintaining healthy bones and muscles, as increased muscle mass could boost your energy and metabolism.8
What Is Metabolism in Relation to Aging, Sex, and Chronic Disease?
There are many factors that impact your metabolism’s ability to perform sufficiently. Among these variables are age, sex, and chronic disease.
Age is something that cannot be overlooked when exploring the question “what is metabolism?” Age brings substantial changes in the regulation of metabolism and body weight. For one thing, leptin—the bodily chemical that helps your brain know when you should stop eating—has weakened signals when you get older, making it harder to tell that you’re no longer hungry.
Aging can also cause changes to the way you process glucose, the sugar the body makes when it’s fed and subsequently uses for energy. These changes can lead to diabetes, as well as a higher risk of heart disease, amputations, blindness, and more. One study from Tufts University demonstrates that dysregulation of energy intake occurs more in seniors—even in individuals that would otherwise consider themselves to be healthy.9
The same study reveals that change in body weight is associated with further consequences for the elderly population—including micronutrient deficiencies, increased hospital admission, frailty, an increased risk of falls and injury, and delayed recovery from those injuries.9 When it comes to lipid metabolism, there is an age-related reduction in fat oxidation and an increase in adiposity as well.10 For these reasons, you should increase physical activity and adjust your diet as you age.
There is also a known age-related decline in protein turnover, or the synthesis and breakdown of protein.11 Protein is a macronutrient that is required for building and repairing tissues and making hormones, enzymes, and other vital body chemicals. It is a building block of muscles, blood, bones, cartilage, skin, hair, and nails.
While men are often thought to have higher metabolisms than women due to increased muscle mass, differences in hormones can also influence metabolism. Sex hormones and chromosomes affect the physiology, structure, and function of several organ systems throughout a person’s lifespan.
One study reveals that sex hormones regulate energy homeostasis and the neuropsychiatric process in the central nervous system.12 According to the same study, malfunction in the central nervous system contributes to schizophrenia, metabolic disorders, and other conditions, like depression and anxiety. Sex hormones—especially estrogen—may have protective effects on lipid and glucose metabolism in our livers, and on perfusion pressure of our kidneys. Conversely, dysregulation could lead to renal and hepatic dysfunction.12
Interestingly, the study also states that women have been documented to have a reduced risk of obesity-related metabolic disorders over men. However, the prevalence of these metabolic disorders does tend to increase in women after menopause. Furthermore, it is less common for premenopausal women to suffer from cardiovascular diseases compared with men of the same age brackets.12
While certain health conditions can influence a person’s metabolic rate, altered metabolic function can affect their risk for chronic diseases.13 The question is no longer simply “what is metabolism?” Instead, it’s “what is metabolic inflexibility?”
Disrupted metabolic flexibility, or metabolic inflexibility, is associated with all sorts of pathological conditions, from metabolic syndrome and type 2 diabetes to cancer.14 The good news is that exercise—both resistance training and aerobic activities—has the potential to reduce the risk of metabolic syndrome.
There is expanding interest among researchers involving the role of metabolism in disease. Conditions like Alzheimer’s disease, Parkinson’s disease, sarcopenia, osteoarthritis, and ocular health are also being examined. Through new and ongoing studies, our ability to understand how metabolism ties into overall health and wellness continues to grow.
This knowledge will be used to bring about enhanced, holistic medicine and a fuller understanding of our bodies and their functions.
Can a DNA Test Really Tell You How to Eat?
As you saw, genes and other factors determine how foods are processed. You’ll no longer have to wonder “what is metabolism?”
With all of the information you’ve read thus far, you’re probably beginning to wonder what actionable steps you can take to improve your health. Knowledge is power. But if you don’t use it to take steps toward a better future, what’s the point?
That’s why we want you to check out this FREE resource. It will guide you further down the highly effective path of using science-backed data to gain a wholesome understanding of people’s individual genetic needs in order to enhance their lifestyles.
You can use this guide to help you make smarter decisions moving forward and create a whole new wellness plan that works specifically for your body.
1. Harms M, Seale P. Brown and beige fat: development, function and therapeutic potential. Nature Medicine. 2013;19(10):1252-1263. doi:10.1038/nm.3361.
2. Mizuno T. Fat Mass and Obesity Associated (FTO) Gene and Hepatic Glucose and Lipid Metabolism. Nutrients. 2018;10(11):1600. doi:10.3390/nu10111600.
3. Chen Y, Michalak M, Agellon LB. Importance of Nutrients and Nutrient Metabolism on Human Health. Yale Journal of Biology and Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6020734/.
4. Galgani J, Ravussin E. Energy metabolism, fuel selection and body weight regulation. International Journal of Obesity. 2008;32(S7). doi:10.1038/ijo.2008.246.
5. Mozaffarian D, Hao T, Rimm EB, Willett WC, Hu FB. Changes in Diet and Lifestyle and Long-Term Weight Gain in Women and Men. New England Journal of Medicine. 2011;364(25):2392-2404. doi:10.1056/nejmoa1014296.
6. Sumithran P, Prendergast LA, Delbridge E, et al. Long-Term Persistence of Hormonal Adaptations to Weight Loss. New England Journal of Medicine. 2011;365(17):1597-1604. doi:10.1056/nejmoa1105816.
7. Müller M. Is there evidence for a set point that regulates human body weight? F1000 Medicine Reports. 2010;2. doi:10.3410/m2-59.
8. Schwingshackl L, Dias S, Strasser B, Hoffmann G. Impact of Different Training Modalities on Anthropometric and Metabolic Characteristics in Overweight/Obese Subjects: A Systematic Review and Network Meta-Analysis. PLoS ONE. 2013;8(12). doi:10.1371/journal.pone.0082853.
9. Roberts SB, Rosenberg I. Nutrition and Aging: Changes in the Regulation of Energy Metabolism With Aging. Physiological Reviews. 2006;86(2):651-667. doi:10.1152/physrev.00019.2005.
10. Toth MJ, Tchernof A. Lipid metabolism in the elderly. European Journal of Clinical Nutrition. 2000. https://www.nature.com/articles/1601033.pdf?origin=ppub.
11. Basisty N, Meyer JG, Schilling B. Protein Turnover in Aging and Longevity. Proteomics. 2018;18(5-6):1700108. doi:10.1002/pmic.201700108.
12. Shi H, Brown LM, Rahimian R. Sex/Gender Differences in Metabolism and Behavior: Influence of Sex Chromosomes and Hormones. International Journal of Endocrinology. 2015;2015:1-2. doi:10.1155/2015/245949.
13. Huang PL. A comprehensive definition for metabolic syndrome. Disease Models & Mechanisms. 2009;2(5-6):231-237. doi:10.1242/dmm.001180.
14. Smith RL, Soeters MR, Wüst RCI, Houtkooper RH. Metabolic Flexibility as an Adaptation to Energy Resources and Requirements in Health and Disease. Endocrine Reviews. 2018;39(4):489-517. doi:10.1210/er.2017-00211.