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What's the Link Between Your Metabolism & Weight?

Medically Reviewed by Carolin Schneider, MD.

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While you've likely heard the term "metabolism," you may not understand what it is, exactly, and how it relates to body weight. In this chemical process, calories are converted into energy, which, in turn, one's body uses to function.When an individual eats more calories than needed, the excess calories are converted to fat, resulting in weight gain. Although the process of metabolism is the same for everyone, the speed at which one's body uses and burns calories hinges on that individual's metabolic rate.

What Is Metabolism?

Simplified, metabolism is an involuntary process that takes place in the cells of our body so that food can be converted into energy. As you're likely aware, a certain amount of calories is needed for one to sustain their vital body functions — maintaining proper hormone levels, repairing cells, breathing, and so on. That basic level of required energy is referred to as one's basal metabolic rate. Different factors impact how fast a person's basal metabolic rate will be — and while some cannot be changed, others are under one's control.

Additionally, there are two phases or parts of metabolism: anabolism and catabolism. During anabolism, the body takes smaller, less complex molecules and converts them into larger molecules. During anabolism, energy is stored in cells for use in the future. During catabolism, fats, proteins, and carbohydrates are broken down and used for energy immediately. Due to our current lifestyle, in which food is available at all times and the daily energy balance often ends with an excess, this balance, consisting of the absorption and release of energy is disturbed.

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Factors Affecting Metabolism

There are many factors which can affect our metabolism. Some of those factors include the following:

Age

As people age, their basic metabolic rate decreases, which means the body needs fewer calories to maintain itself. If exercise or calorie intake is not adjusted accordingly, weight can start to creep on as people age.

Sex Assigned at Birth

Female individuals tend to have a slower metabolism since, on average, they have less lean muscle.

Genetics

To some extent, a person's metabolic rate is inherited through their genes.

Diet

Eating too few calories can actually cause metabolism to slow down. Deficiencies in the diet may also lead to problems with the endocrine system and cause metabolic disturbances.

Exercise

Regular exercise can teach the body to burn calories at a faster rate. Exercise can help build muscle mass, which also increases metabolism.

Microbiome

The so-called gut-liver axis plays a central role in understanding the human energy supply. The symbiotic community of the organism with bacteria, fungi and viruses in the intestine plays a central role in the effective intake of food. In the past, this system was optimized over thousands of years in order to extract as many nutrients as possible from the food supplied. While food components are absorbed in the intestine and transported to the liver via the portal vein for further processing, the transfer of bacterial components or toxins must be prevented in order to avoid systemic bacterial translocation. Therefore, changes in your microbiota can affect your metabolism.

The Connection Between Weight & One's Metabolism

For thousands of years the human environment was rough and a large part of the lifetime was characterized by getting enough food. Lack of food, infections and wars meant that the average life expectancy was low and a genetic profile was selected that enabled survival under these conditions. In particular, the food intake was irregular. After all, the body was designed to cope with times of starvation.

The transition to the industrialized world took place within a few generations, so no genetic adaptation could take place. The genetic makeup of modern humans continues to correspond to that of our ancestors from the Stone Age when we were still hunters and gatherers. In the meantime, both the daily energy expenditure and the eating habits have changed dramatically in the context of the western lifestyle.

Therefore, weight and metabolism are directly connected in a few ways. When metabolism is slower, the body needs fewer calories to sustain itself. Therefore, if there is no decrease in food intake as the body's metabolism begins to slow down, weight gain will occur. Inversely, if the metabolism becomes faster, but there is no change in food intake or food intake decreases, a person will lose weight.

Besides, it is necessary to remember that the rate at which a person's body converts the calories in food into energy varies individually, and not everyone has the same calorie needs. In addition, an individual's metabolic rate can change over time and is influenced by age, stress and several other conditions.

Metabolic Disorders Associated With Weight Gain

Hormones, which are produced through the endocrine system, play a large role in the regulation of the metabolism. In particular, the thyroid gland produces hormones, which affect the rate at which metabolism takes place. There are certain disorders of the thyroid gland which lead to unintentional weight gain or loss. Two of the most common disorders include the following:

Hyperthyroidism occurs when excess thyroid hormones are released into the body due to an overactive thyroid gland. These hormones cause metabolism to speed up, which may lead to weight loss.
Hypothyroidism is the opposite condition and develops when the thyroid gland is inactive. Too few hormones are released into the body, and metabolism slows down, which can result in weight gain.

Metabolic Rate

While it is clear a person's metabolic rate may play a role in weight management, it is not the only factor that should be looked at. Eating unhealthy, fatty foods, overeating, and living a sedentary lifestyle all contribute to weight gain and are usually more to blame than a slow metabolism. Still, it's important to understand the role metabolism can play in weight management. With proper knowledge, certain changes can be made to increase metabolism, which can help in reaching weight loss goals.

If you're looking to aid your metabolism, some factors to look at include:

Diet

Make sure to eat enough. Eating too few calories and restricting diet too much can have an impact on your weight. What happens is, the body reacts to fewer calories by believing it is being starved, so it slows metabolism down. However, eating small, frequent meals may be a little boost for the metabolism. Every time a person eats, the body needs to use energy to digest the food. On the other hand, you should not exceed your daily calorie limit and especially intermittent fasting is beneficial for your metabolism.

Exercise

Exercise regularly, including strength training. Increasing lean muscle mass may increase metabolism to some extent. As lean muscle is increased in the body, calories are used at a faster rate.

Microbiome

Your microbiome can play a crucial role in your metabolism. A healthy lifestyle can contribute to a favorable microbiota in your gut.

Sleep

Sleep is connected to various metabolic processes and is important to maintain an active metabolism. Sleep deprivation and sleep disorders have metabolic implications. To boost your metabolism, make sure you get enough sleep.

We've also compiled some great ways to kickstart your metabolism — and we've rounded up 10 foods that can aid you in making those changes.

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Resource Links:

"Energy metabolism, fuel selection and body weight regulation" via HHS Public Access, U.S. National Library of Medicine
"Analysis of energy metabolism in humans: A review of methodologies" via Elsevier, U.S. National Library of Medicine
"Sleep and Metabolism: An Overview" via International Journal of Endocrinology, U.S. National Library of Medicine
"Increasing muscle mass to improve metabolism" via Adipocyte, U.S. National Library of Medicine
"Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting" via HHS Public Access, U.S. National Library of Medicine