Your metabolism is the process by which your body converts what you eat and drink into energy. Every time you eat, digestive enzymes in your body break down the food and turn it into energy that your body needs to function on a daily basis.
When we’re younger, our metabolisms are quicker because we are constantly growing which requires more energy–so we’re burning more calories and fat. However, as we age our metabolism naturally slows down and, according to this “Self” magazine article, we also lose muscle mass.
As women age, they lose estrogen, and as men age, they lose testosterone — both of which contribute to higher fat and lower muscle mass. Since muscle tissue burns more calories and fat and boosts your resting metabolism, a loss of muscle mass means you will burn fewer calories throughout the day. Read more about this here.