Your metabolism slows as you age. You may need to cut calories to prevent weight gain. On the other hand, some people find that they don’t get as hungry or thirsty as they used to. As you eat less, choose foods that pack more nutrients into fewer calories, such as fruits and veggies, whole grains, low-fat dairy, and lean protein. Changes in your body could leave you short of vitamins D and B12, so you might need supplements, too.