The Truth About Metabolism


SupplementsYou blame your weight on a slow metabolism, choose a supplement because it promises to rev your metabolism, and add more protein to the diet because you’ve heard it helps melt away unwanted pounds. Is there a thread of truth to any of these beliefs?

First, it’s important to define metabolism. Metabolism is the process by which your body converts what you eat and drink into energy. During this complex biochemical process, calories in food and beverages are combined with oxygen to release the energy your body needs to function. Even when you’re at rest, your body needs energy for everything from breathing, circulating blood, and adjusting hormone levels to growing hair and repairing cells. The amount of energy to maintain these functions is called your “basal metabolic rate,” or BMR,  which is influenced by genetics, your height and weight, gender, and age.  About 70% of the calories you burn every day go to BMR. Another 100 to 800 calories every day go to digesting, absorbing, transporting, and storing foods you eat.  Physical activity accounts for the rest of the calories your body burns up each day and is by far the most variable of the factors that determine your calorie needs.

Before we get to what works for boosting metabolism, let’s discredit a few myths. There is no research to support food combining, protein-rich diets, or any particular food as a way to kick metabolism into high gear. Some spices, such as cayenne, have a slight, temporary effect on metabolism, but not enough to produce a drop in weight. There is no such thing as “negative calorie” foods, and being overweight is not a result of sluggish glands, unless you have an underactive thyroid gland.

The most important habit to adopt to improve metabolism is exercise. Body fat is like a storage box sitting on a shelf, thus using few calories to maintain its existence. In contrast, muscle is active, calorie-burning tissue that demands more energy while being used, repaired, and even when the body is resting. In general, the more muscle you build and maintain, the higher the metabolism. Aerobic activity also burns calories.

While muscle-building exercise increases metabolism, other factors can slow it down.  According to the National Weight Control Registry, being overweight at some point in a person’s life, has a permanent effect on metabolism. In their study of people who have lost a significant amount of weight and kept it off, it appears to take more exercise to maintain that weight loss than it does for someone who never gained the weight in the first place. Sleep deprivation also results in a slow-down of metabolism. Stress indirectly leads to problems with metabolism. People with high levels of cortisol, a stress hormone, tend to be overweight, and in turn, that excess body fat slows metabolism. Lowering cortisol levels can start a chain reaction that can help metabolism run more effectively.

In short, your ability to lose weight and maintain a desirable body weight comes down to balancing calories in from food with calories out from activity. If you are gaining weight, you’re eating too much or moving too little. If you’re losing weight, you are burning more calories than you are taking in.

Elizabeth Somer, M.A.,R.D.

Shechter A: Obstructive sleep apnea and energy balance regulation. Sleep Medicine Reviews 2016; July 15th.

Quatela A, Callister R, Patterson a, et al: The energy content and composition of meals consumed after an overnight fast and their effects on diet induced thermogenesis. Nutrients 2016;October 25th.


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