We’ve all heard the word metabolism, but do you know what it actually is?

Metabolism is the process by which your body converts what you eat and drink into energy your body needs to function.

This can process can be faster or slower depending on a few variants, and you can actually control how slow or fast your metabolism is with your food intake and exercise regime.

Let’s get into the science of it.

(Prefer to listen instead? Check out my podcast episode on this topic here.)

We all create energy mostly from glucose (blood sugar), and from ketones (from the breakdown of fat).

The energy that your body needs to function is called your energy expenditure. Energy expenditure is made up of 3 things:

  • Resting metabolic rate
  • Physical activity
  • Dietary thermogenesis (energy needed for digesting food)

An increase in body tissue, either muscle or fat, increases your resting metabolic rate. This is the energy required to fuel the body’s functions down to the cellular level.


Increased weight = increase in metabolism.

Weight loss = decrease in metabolism.

It makes sense. If you have more body tissue overall, your body has more functions to support. It must get blood and oxygen to all the tissues and must complete more cellular processes.

It’s important to note that resting metabolic rates are different in everyone and we do not have enough evidence to say that a higher or lower metabolism predisposes someone to weight gain.

Having said that, athletes are in a different category. For example, someone who is lean and building large amounts of muscle may increase caloric intake and increase their resting metabolic rate, but this does not apply to the average person trying to lose weight.

In non-athletes, 70% of the daily energy we use is from our resting metabolic rate, 20% is from physical activity, and only 10% of the energy we use up is from diet-induced thermogenesis.

Increasing muscle mass with resistance training, such as lifting weights or using resistance bands, can make a big difference. The more muscle mass you have, the less your metabolism will slow as you lose weight. This means that instead of your resting metabolic rate going down while you lose weight, you can keep it up.

For someone who is “lean,” the energy that muscles use while you are resting can be approximately 3 times higher than fat. The daily metabolic rate of muscle could be 13 kcal/kg/day and adipose tissue (or fat) 4.5 kcal/kd/day. This varies depending on the muscle to fat ratio. On the other spectrum, if you have hundreds of pounds of body fat the resting energy, the metabolic rate, will increase to maintain the fat tissue.

The bottom line

The reason you are overweight is not that you have a “low metabolism.” In fact, if you have excess body fat, you most likely have a “faster metabolism.” As you lose weight your metabolism slows down.

How can we apply this information?

The goal is not to have a “fast metabolism.” The goal is to use energy in your body efficiently.

The best two ways to do that are to;

  1. Stop grazing & snacking through the day. Plan to eat 2-3 meals per day and leave the snacking behind.
  2. Maximize your exercise results. Schedule time for exercise. Keep changing up the type of exercise you are doing. If you continuously do the same thing your body becomes efficient at it and it stops being as effective. You can use more energy when your body is constantly doing new things.


Wang Z, Ying Z, Bosy-Westphal A, et al.: Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure. Am J Clin Nutr 2010 92:1369-1377. https://www.ncbi.nlm.nih.gov/pubmed/20962155
Pontzer H, Durazo-Arvizu R, Dugas LR, et al.: Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans. Curr Biol 2016 26:410-417. https://www.ncbi.nlm.nih.gov/pubmed/26832439

Till next time, stay healthy.

Dr. Kristine LaRocca


Disclaimer: Although I am a medical doctor, I am not YOUR doctor. So the things I teach are not to be used as medical advice. You should consult your physician to discuss what is best for you personally.

If you would like to become my patient, schedule a free consultation below.

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