What is it exactly?

Most people have an idea of what metabolism is, but it’s often not a complete, accurate picture. Many components affect metabolism, which is essential to how your body functions. Many people assume that you can alter it. Is this belief correct? What impacts does your metabolism have?

No matter what you’re doing, your body is always working and using energy, which comes from the food and drinks you consume. Your metabolism is a series of processes that control how your body creates and uses energy. These processes include breaking down nutrients from our food and those that build and repair our bodies. The amount of energy is measured in kilojoules (kJ). Metabolism is broken down into two processes: anabolism and catabolism. Anabolism is the part of metabolism in which our body is built or repaired. It helps with the storing of energy, supporting new cells, and maintaining body tissues. The process requires energy that comes from your food. If you eat more than you need for daily anabolism, the excess nutrients are stored as fat. Catabolism is the opposite. It’s the breaking down energy to move, heat, and energize your body. This is done by breaking food components (such as carbohydrates, proteins, and dietary fats) into simpler forms.

Components of Metabolism

Your metabolism measures, or total energy expenditure (TEE), can be divided into three components. Your basal metabolic rate (BMR) is the amount of energy your body use at rest. This helps to keep all its systems functioning correctly (such as breathing, keeping the heart beating to circulate blood, growing/repairing cells, and adjusting hormone levels). It accounts for the largest amount of energy expended daily (50 – 80%). Your BMR is primarily determined by your total lean mass, especially muscle mass, because lean muscle mass requires a lot of energy to maintain. Essentially, the more muscle mass you have, the more kilojoules you will burn. Also, anything that reduces lean mass will reduce your BMR. This is why it’s essential to preserve or even increase your lean muscle mass through exercise when trying to lose weight. Usually, it means combining training, such as weight-bearing and resistance exercises, with eating healthier rather than just changing diet alone.

The thermic effect of food (thermogenesis) is the amount of energy your body uses to digest the foods and drinks you consume and absorbs, transports, and stores their nutrients. It accounts for about 5 – 10% of your energy use. Your BMR rises after you eat because you use energy to eat, digest and metabolize food. This starts soon after you start eating and peaks two to three hours later. The increase can range between 2 – 30 % depending on the size of the meal and the types of foods you’ve eaten. For example, fats raise the BMR 0 – 5%, carbohydrates 5 – 10%, and proteins 20 – 30%. Hot spicy foods, like chili, horseradish, and mustard, can have a significant thermic effect.

Energy used during physical activity is the energy used by physical movement. It varies the most depending on how much energy you use each day. It can include planned exercise (like going for a run or playing sport) and all incidental activities (such as hanging out the washing, playing with the dog, or even fidgeting!). This incidental activity is called non-exercise activity thermogenesis (NEAT) and accounts for about 100 to 800 calories used daily. Based on a moderately active person (30–45 minutes of moderate-intensity physical activity per day), physical activity contributes 20% of daily energy use. Our muscles may burn through as much as 3,000 kJ per hour during strenuous or vigorous physical activity. However, estimating the energy spent during exercise is difficult because the actual value for each person will vary.

Calculating Your BMR

To determine your metabolic rate, you need to calculate your BMR. The most accurate way to do this is to have it tested in a lab. Sometimes, health clubs offer it for a fee. Another option is to calculate your estimated BMR. Online calculators are available or, if you’d prefer to calculate this number by hand, you can do so by using the Harris-Benedict Equation:

Men: 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years) = BMR
Women: 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years) = BMR

Once you have your BMR, you can then figure out your total metabolic rate. This is a combination of BMR and the calories used throughout the day. The easiest way is to use a fitness tracker. For example, if you burn 700 calories from daily movement and your BMR is 1200 calories, your total metabolic rate would be about 1900 calories. This means you need to consume 1900 calories a day to maintain your weight. If you take in less, you’ll lose weight. However, if you take in more, you’ll gain weight.

Are Basal Metabolic Rate and Resting Metabolic Rate the same?

Your basal metabolic rate is slightly different than your resting metabolic rate (RMR). Often, the terms are mistakenly used interchangeably. Your RMR is the number of calories your body would need if you were to do nothing for the next 24 hours. It’s calculated by measuring oxygen consumption and carbon dioxide exhalation after a person has been seated or lying down for at least 15 minutes and hasn’t exercised in the previous 12 hours. Several online calculators, including the one by the National Institutes of Health (NIH), estimate your RMR.

What affects your metabolism?

Metabolism can vary a lot between people, and researchers aren’t sure why. Several factors impact your metabolism.

Genes. Your genes are the blueprints for the proteins in your body, and they’re responsible for the digestion and metabolism of food. Sometimes, a faulty gene means your body produces a protein that is ineffective in dealing with our food, resulting in a metabolic disorder. In most cases, genetic metabolic disorders can be managed under medical supervision, with close attention to diet.

Hormones. They help regulate metabolism. Hormonal imbalances can influence how quickly or slowly the body burns energy. Some of the more common hormonal disorders affect the thyroid, which makes hormones that regulate many metabolic processes, including energy expenditure.

Age. A common myth is that age causes your metabolism to slow. In actuality, metabolism slows with age due to loss of muscle tissue and hormonal/neurological changes. Another issue is that as we get older, we aren’t as physically active as we once were, but our diet may not change to suit our body’s needs. The effect happens gradually, even if you have the same amount of fat and muscle tissue. Continual decline starts as young as age 18. Research has shown that strength and resistance training can reduce or prevent this muscle loss.

Body size/composition. Larger people have more muscle mass and usually need more calories because their BMR is higher. The amount of lean muscle tissue a person has significantly impacts their BMR. That’s because muscle uses a lot more energy than fat while at rest. This is why it’s thought that you’ll have a higher resting metabolism if you can build up your muscle and reduce your body fat.

Gender. Men usually have faster metabolisms than women because they tend to be larger. Also, research indicates that this could be due to females conserving energy and storing fat more efficiently than their male counterparts because it appears that differences in various hormones may play a role.

Stimulants. These include caffeine, tea, or nicotine, and they can increase the BMR for short periods.

Diet. This plays a huge role in metabolism. Crash dieting, starving, or fasting (basically eating too few kilojoules) encourages the body to slow the metabolism to conserve energy. In fact, BMR can drop by up to 15%. Unfortunately, lean muscle tissue is also lost, which further reduces BMR. On the other hand, the popular strategy of eating frequently to avoid “starvation mode” may cause weight gain, especially if you end up eating more than your body needs. It’s important to realize that everyone loses weight when they burn up more calories than they eat. To lose weight, you need to create an energy deficit by eating fewer calories or increasing the number of calories you burn through physical activity or both. The Dietary Guidelines for Americans recommends cutting calories by 500 – 700 calories a day to lose 1 – 1.5 pounds a week. Foods with protein are more difficult to digest and support muscle mass growth, especially if you strength train. Fiber also makes your body work harder because it’s more challenging to chew and break down. Spicing up your food is another way to boost body temperature to burn more calories (it only has a small impact, though). Some research has found that extra water consumption can also increase your resting metabolic rate. A healthy diet with a suitable amount of calories and consistent meals will give your body the energy it needs.

Exercise. It’s the most critical aspect in boosting your metabolism. The more active you are, the more calories you burn. Aerobic exercise is the most efficient way to burn calories. As a general goal, include at least 30 minutes of physical activity in your daily routine. An intense workout program revs up your metabolic engine for hours following a session. Some high-intensity interval training can rev up your metabolism for as much as a full day. Experts also recommend strength training exercises at least twice a week because it helps build muscle. Do heavy resistance training to slow the rate that you lose muscle mass beginning in your late 30s or early 40s. Holding on to as much muscle as you can with age will keep your metabolism higher. Some other tips are to modify the way that you carry out household chores to increase your heart rate, take an extra trip up the stairs, pace around while you chat on the phone, or stand while you work on your laptop to prevent your body from staying sedentary for extended periods.

Sleep. Sleep is vital to regulating your blood sugar. If you don’t get good, quality sleep, your body will have trouble with glucose levels, leading to a lack of energy. Boosting your metabolism through diet and exercise will also help your body burn more calories while at rest.

Environmental temperature. If the temperature is very low or very high, the body has to work harder to maintain its normal body temperature, which increases your BMR. The body uses as much as 40% of its total energy expenditure to keep its temperature stable.

Can you speed up your metabolism?

Speeding up your metabolism is highly unlikely despite many methods that claim to do. Unfortunately, these either don’t work or won’t create lasting results. These products are often more hype than help, and some may cause undesirable or even dangerous side effects. Dietary supplement manufacturers aren’t required by the Food and Drug Administration (FDA) to prove that their products are safe or effective. Supplement makers tout ingredients such as green tea, caffeine, capsaicin, selenium, and more, either individually or together, as metabolism boosters. However, while some have been shown to increase the rate at which people burn calories slightly, it’s not to the extent that it will make a significant difference over time.

What is adaptive thermogenesis?

Adaptive thermogenesis is a seemingly permanent reduced resting metabolism in people who have lost a large amount of weight, especially if it was done rapidly. It makes sense that losing weight will slow down the metabolism since slimming down generally involves muscle loss. Also, when the body is smaller, it doesn’t have to work as hard to keep running. However, researchers have found that the slowdown after weight loss often appears to be substantially greater than makes sense for a person’s new body size. One theory is that it may be the body’s way of defending a specific weight range, called the set point. If you gain weight and keep that weight on for some time, the body gets used to it. When that weight drops, many subtle changes kick in (ex. hormone levels and brain) slowing the resting metabolism. However, it also increases hunger and decreases satiety from food. It seems the body’s goal is to get back up to that set point weight. However, researchers don’t fully understand why this metabolic slowdown happens.

Can you maintain weight loss?

On average, 15% of people can lose 10% of their weight or more and keep it off. The key is finding lifestyle changes you can stick to over a long time. It’s also vital to view those as changes needed to control diseases, like obesity. According to a study from the National Weight Control Registry, there are certain traits, habits, and behaviors of those who’ve lost at least 30 pounds and kept it off for a minimum of one year. The study has more than 10,000 members, who answer annual questionnaires about how they’ve managed to keep their weight down. Some of the things they have in common are weighing themselves at least once a week, exercising regularly at varying degrees of intensity (most common is walking), restricting calorie intake, staying away from high-fat foods, eating breakfast, and watching portion sizes.

It’s easy to blame problems with weight on metabolism. However, weight is a complex process that involves genetics, hormones, diet, lifestyle, sleep, physical activity, and stress. The reality is that metabolism often plays a minor role. The most significant factors as you age are often poor diet and inactivity. A balance of good habits will help your metabolism recognize a new ideal weight. You might not be able to control your biology, but you can control your choices.