Try guessing the answers to the following two questions, readers.

1. What percent of our energy is burned during physical activity? (Assume average daily activity.) And 2. What percent of our energy is burned while we’re just sitting or sleeping?

First, readers may be surprised to learn our bodies use about 10 percent of our energy just to generate more energy in the first place. Converting the food we ingest to energy is a complex biochemical process called metabolism. This includes digestion (breaking down food into usable components) and distributing these products to the bloodstream, etc. It also includes elimination of undigested food and other waste.

Our bodies use another 20 percent of our energy during physical activity. This may be short and energetic, such as running, or it may be slow and easy, like walking the dog. Even bending over to pick up the keys you dropped counts. Long and intense activity also utilizes the aerobic system, which breaks down fat stores for more energy.

And then there’s doing nothing much, such as watching a movie or snoozing. This uses the most energy by far—anywhere from 50 to 80 percent, depending on your body, age, lifestyle and more. But why? Maintaining the body’s vital activities such as breathing, circulating blood and organ function requires energy. Just staying alive takes work.

Dear Marilyn, Our bodies use energy to generate heat and to move our muscles. Are there any other ways our bodies use energy?

—Alyssa Dare, Elkridge, Maryland