Keep an eye on fat. As you age, your metabolism slows, and so your calorie needs decrease. Fat is relatively high in calories so be sure to eat only moderate amounts of healthy kinds (like monounsaturated fats in olives and avocados and omega-3s in fish). Limit saturated fats by choosing lower-fat versions of milk, yogurt and cheese and opting for fish, lean poultry and legumes in place of fatty red meats. Keep in mind that many low-fat or fat-free products—even healthy ones like yogurt—often contain added sugars, which bump up the calorie content. Read labels.