The Truth about Slow Metabolism

Our bodies need a constant supply of energy. The very same activities that keep us alive (breathing, thinking, moving) require our cells to continuously break down nutrients. Some people believe that they gain weight because their cells are lazy and don’t break enough nutrients, letting the excess accumulate. They claim to have a “slow metabolism”. But does it really exist? And if so, can it be accelerated?

There are a number of things that affect how much energy we use during our resting state. One of them is our overall body size, with larger bodies requiring larger amounts of energy. Another one is the percentage of muscle and fat in our bodies. Muscle cells require more energy than fat cells, so the higher the proportion of muscle in your body, the higher your metabolic rate will be. Age is also an important factor, with metabolic rates decreasing over time, probably because we tend to accumulate fat and lose muscle as we age.

To a certain extent, it is possible to tweak these parameters to increase the metabolic rates. For example, if you work out, you’ll be losing fat and gaining muscle, thus “accelerating” your metabolism. However, there is currently no way to stimulate the activity of your cells artificially, be it by specific foods and drinks or by any other means (please read ‘A Pill To Lose Weight?‘ to learn about the risks of trying to lose weight “the easy way”).

The claims that some food can speed up your metabolism have limited scientific support. It is often heard, for example, that spicy foods can speed up metabolism. But while it is true that they do raise body temperature and stimulate cellular activity, the effect is so transient that its impact on basal metabolism is negligible, let alone in fat accumulation.

You might have also heard that eating before going to sleep promotes weight gain. The rationale behind this claim is that when you sleep your metabolic rate is lower, and hence your body accumulates more fat. The truth is that although our bodies do use less energy when we sleep, they still burn nutrients. What’s important is how much you eat during the whole day, and not so much if you eat it before going to sleep (see ‘10 Nutrition Myths”).

To sum up, it is very unlikely that slow metabolism might be the reason underlying someone’s weight gain. Except some rare medical conditions, such as the Cushing’s syndrome, basal metabolic rates seem to be pretty constant among individuals, once corrected for muscle and fat composition.

However, there are foods that are more rapidly metabolized than others. In this case, slow-digesting foods are a better choice for losing weight. Fiber, for example, takes longer to be absorbed by your body. This means that when you eat fiber your body is busy for a longer time, prolonging the feeling of fullness and keeping your cravings at bay (check out ‘The Importance Of Fiber‘ to learn more about the benefits of fiber).

So remember, if you want to befriend your metabolism, keep you food options healthy and exercise regularly!

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About Author

Hi, my name is Emilio Greenberg and I work on obesity research. I graduated in Biology and later did my Master's degree in Madrid, where I met Sarah ("How I've met Emilio"). I now hold a PhD in Molecular Biology and am Assistant Professor at the University, so I spend my time between the bench and the classroom. My research focuses on human metabolism, obesity and the influence of different diets in our health. I try to understand how our bodies process the food that we eat and how our eating habits influence our susceptibility to disease. We are currently living an epidemics of obesity that needs to be tackled. I hope that through this series of articles I can help you understand the crucial importance for your health of keeping a balanced diet. Because, as much as a cliché as it may sound, we truly “are what we eat”... continue reading

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