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Do Diet Pills Ruin Metabolism?

By Sarah Nyako ; Updated July 18, 2017

Some ingredients in diet pills, such as caffeine, work to stimulate our systems, which can cause a temporary increase in our metabolic rate. However, diet pills can also have the reverse effect, particularly if they lower the amount of muscle mass we have. If not used under medical supervision, diet pills can actually sabotage weight loss efforts.

About Diet Pills

There are many different types of diet pills. Some work by giving you energy to maintain a more active lifestyle and burn more calories. Others suppress your appetite, causing you to eat less and experience fewer cravings. Others flush your body of water weight or stimulate bowel movements that can cause temporary weight loss. Some pills contain a combination of ingredients that perform many of these functions. The only FDA-approved over-the-counter diet pill, Orlistat, actually prevents the absorption of dietary fat.

Understanding Metabolism

To understand how diet pills can affect our metabolism, it is important to understand what exactly metabolism is. The word refers to a complex system that converts food into energy. Both the food we eat and the energy we burn can be expressed in a unit called a calorie. The total amount of energy our bodies process in a day to perform all the necessary functions is known as our basal metabolic rate. Many things can affect the number of calories our bodies burn, such as weight, age, gender, physical activity and body composition.

Loss of Muscle Tissue

It is important to note the effect of body composition on metabolism. Muscle tissue is more metabolically active than fat. That means it takes more energy to maintain muscle mass than it takes to maintain fat mass. If you take two people of the same height and weight, the individual with the greater percentage of muscle mass will burn more calories in a day. That means their metabolism is higher, they can eat more to maintain their weight, and will have an easier time losing weight. It also means that if they are in a state of deprivation, their bodies will burn the muscle tissue first, so that it can conserve energy. In this way, diet pills that greatly suppress appetite can have the opposite of the intended effect. It can cause people on them to eat too little, which will cause a loss of muscle mass and a reduction of metabolism.


If you are curious about using a diet pill, discuss it with your doctor. Many contain ingredients that may be harmful to you or that may interact negatively with a current condition or medication. If you do decide to try a prescription diet pill, follow the directions carefully. Additionally, make sure to eat at the very least 1,200 calories if you are a woman and 1,500 if you are a man. If you are interested in using a diet pill for energy or appetite control, look instead to changing your lifestyle to increase energy. Getting enough sleep and eating several smaller nutritious meals throughout the day can keep your blood sugar and energy levels steady.

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