Your Metabolism Balances Using Energy and Storing Energy
Metabolism is a two-step process between catabolism and anabolism. The balance between the two is controlled by hormones, chemicals released by cells that have specific functions. Hormones are either classified as anabolic or catabolic depending on what they do:
Catabolism breaks down macronutrients into their smaller units to release energy for physical activity or to use for anabolism. For example, the catabolic hormone cortisol is released in response to stress, causing your body to break down muscle protein to use for energy.
Anabolism builds up larger molecules from smaller units requiring units of energy — for example, creating hormones, enzymes, and compounds for cell growth to build bone and muscles. The anabolic hormone insulin, for example, controls the amount of glucose in your blood by converting it into compounds that cells can use or store. The sex hormones testosterone and estrogen are also anabolic hormones that work to develop male and female sex characteristics.
Your body weight depends on your body’s catabolism minus anabolism, or the amount of energy your body takes up to use. If your catabolism greatly exceeds anabolism, the excess energy generated is stored as glycogen (for later use by your muscles) or fat (which serves to increase body weight). Many factors impact which state your body favors, and everyone is different.
Here are some reasons your metabolism may be on the fritz:
Calorie intake: If you’re eating more calories than you can use, your body will store them for later.
Activity level: If you’re not active enough, aren’t doing any weight-resistant exercise to work your muscles, or are too active that your body is stressed, you can be said to be in a more catabolic state.
Age: One reason why losing weight becomes more difficult as you age is that levels of your anabolic hormones, which use up that excess energy, like testosterone or estrogen, decrease, resulting in decreased muscle mass and increased fat storage.
Genetics and hormone-disrupting conditions: Based on individual differences in genetics, you may be more or less prone to a sluggish metabolism. Also hormone-disrupting conditions like menopause and hypothyroid play a role.