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Mythbusting: Metabolism

What Is Metabolism?

Metabolism is the process of converting food and drink into energy.1 This complex process involves a series of chemical reactions in our bodies that transforms what we eat and drink into the energy we use to carry out our daily activities and most basic functions, like breathing and maintaining a heartbeat. All living things undergo this vital process, not just humans.

Metabolism can be divided into two categories: anabolism and catabolism.1 The body regulates these two chemical processes to keep them in balance with each other.

Anabolism involves a “building” process: Energy (in the form of calories) is used for bodily functions – especially those related to growing and repairing cells in your body.1

Catabolism involves “breaking down” functions: Food and drink are reduced to simpler forms that the body can use.1 This process releases energy.

Metabolism occurs in every single cell in our bodies. We’re always burning energy, even when we’re sleeping, and we need sufficient energy to keep our metabolisms up and running efficiently.1

Is Metabolism Genetic?

Although it’s very common to hear claims about products or diets that can “boost your metabolism,” these claims are unproven, inaccurate and, often, not physiologically possible. Changing the rate of your metabolism is not as simple as taking an herbal supplement and immediately burning body fat.

Metabolic rate, or the amount of energy (calories) your body uses over a period of time, is, to some extent, genetically determined. Other factors, such as age, gender, muscle-to-fat ratio, amount of physical activity and hormone function, contribute to how “fast” or “slow” this process functions.

The number of calories, or energy, used in metabolic processes can be divided into three main categories:

  • Resting Metabolic Rate (RMR): This is the amount of energy your body needs for basic functions at rest, such as breathing, pumping blood and basic neurological functions.2 RMR comprises around 60 to 80 percent of your total energy expenditure.3
  • Thermic Effect of Food (TEF): Your body needs energy to digest the food you eat. This accounts for around 10 percent of your total energy expenditure.3
  • Physical activity: The amount of energy your body spends on physical activity depends on how much physical activity you engage in and how intense it is. Typically, physical activity accounts for around 10 to 30 percent of your total energy expenditure.

As mentioned earlier, genetics can influence metabolic rate to a certain extent. This helps explain why some individuals can take in a large amount of energy (calories) and not gain weight, while others tend to gain weight while eating less food. One review of studies found that about 40 percent of individuals’ differences in energy usage, including their resting metabolic rate, thermic effect of food, and the energy cost of low-to-moderate intensity exercise, are due to inherited characteristics.4   

However other factors also come into play. As we age, we are not only less physically active, but we also lose muscle mass. Muscle mass (or “fat-free mass”) is metabolically active tissue, meaning it uses up energy. Having less muscle mass may result in using energy at a slower rate. One review of studies suggests that the age-related decrease in metabolic rate is due not only to the natural loss of muscle mass, but to a decrease in the mass and metabolic rate of organs and body tissues as well.5

Gender also influences metabolic rate. Women tend to burn fewer calories than men of comparable age and weight because women naturally have less muscle mass.

As you can see, metabolism is not a simple, single entity that we can easily manipulate up or down. However, there are some modifiable factors that can affect metabolic rate. Let’s explore them.

Does Eating Less Lower Your Metabolism?

In short, yes. Let’s see how this works. 

The body is biologically wired for energy conservation, though not necessarily for weight loss. In fact, your body interprets eating less food than it needs as being under starvation conditions and eventually adapts to function at a lower metabolic rate. Interestingly, this is a protective mechanism, as the body fights against the threat of not getting enough energy.

When we eat fewer calories than our body needs to carry out its biological functions, our bodies preserve energy by adapting to a lower metabolic rate, making weight loss that much harder with each low-calorie diet. Furthermore, as we lose weight, our bodies undergo hormonal changes that increase appetite and decrease satiety, making it even more difficult to lose and maintain weight.6

Thus, unhealthy practices such as skipping meals, following fad diets, or drastically restricting calories can contribute to slowing down your metabolism. In addition, your body needs not only energy, but nutrients such as carbohydrates, fats, protein, vitamins, and minerals to function optimally. Restrictive diets put you at risk for deficiencies in these important nutrients.

How to Improve Your Metabolism 

Although our metabolic rate is, for the most part, out of our control, we can help support it by practicing healthy lifestyle habits. We can’t really “speed it up”, but we can keep it as healthy as possible. Here are some habits you can incorporate to help your body use energy more efficiently.

Action Steps

  1. Stay physically active throughout your life. Regular physical activity can help keep you fit, flexible, and mobile. It also affects the efficiency with which your body metabolizes certain substances. In one well-designed study, 80 days of regular aerobic and strength exercise significantly influenced the way men’s muscles metabolized fatty acids and ketone body substrates (both sources of energy), and other substances in the body.7 Always consult your healthcare provider before changing your exercise routine. 
  2. Incorporate resistance exercise into your workout routine. We tend to lose muscle mass as we age, which contributes to a slower metabolic rate. Resistance exercise helps preserve muscle mass, and, thus, may help slow the decline of your metabolic rate. Free weights, weight machines, or movements that use your own body as resistance (such as push-ups) are some great options.
  3. Follow a balanced, varied diet. Your body needs consistent energy to function properly and avoid slowing down its metabolic rate. Eating a wide variety of foods not only supplies you with sufficient “fuel”, but also ensures you get all the nutrients your body needs. Try to include nutrient-dense foods such as whole grains, fresh fruits and vegetables, lean proteins, and healthy fats in each of your meals. Your metabolism – and your overall health – will thank you for it.


Rx Only. For the safe and proper use of Plenity or more information, talk to a healthcare professional, read the Patient Instructions for Use, or call 1-844-PLENITY.

The opinions provided in this article are those of the author alone, and in no way imply an endorsement by Gelesis Inc. The information in this article should not be used as a substitute for talking with your health care professional. Always talk with your health care professional about diagnosis and treatment information.