Your goal is to keep your body mass index -- a ratio that compares height to weight -- in the "normal" range of 18.5 to 24.9. When you creep over 25, you're considered overweight, and once you hit 30 or more, you're classified as obese, a condition that comes with myriad health risks. You can help prevent obesity, however, by focusing on consuming a healthy diet that includes portion-controlled foods containing all three vital macronutrients.
Sources of Carbohydrates
Carbohydrates provide your body's preferred source of fuel, but you should choose your carb sources wisely and consume them in moderation. Harvard Medical School notes that low-carb diets can have weight-loss advantages, but when it comes to preventing weight gain, it's more important to focus on quality carbohydrates. Skip refined grains such as white bread, processed breakfast cereals and white rice, and go for healthier carbohydrates such as fresh fruits, vegetables -- both sources of carbohydrates as well as vitamins and minerals -- and whole grains such as oatmeal, brown rice and whole-wheat bread. The Dietary Guidelines for Americans 2010 recommends that 45 percent to 65 percent of your calories come from carbohydrates.
Despite the low-fat fad of the 1980s and 1990s, Harvard Medical School says that the evidence doesn't support reducing fat overall to prevent weight gain or lose weight -- mostly because low-fat diets tend to be high in carbohydrates. Instead, follow the U.S. Department of Agriculture's dietary guidelines, and eat approximately 20 percent to 35 percent of your calories from healthy, unsaturated fats. Sources of monounsaturated fats include nuts, avocados, olive oil, vegetable oils and canola oil, while polyunsaturated fats come from walnuts, flaxseeds and fatty fish such as salmon.
Don't Forget Protein
Dietary Guidelines for Americans 2010 recommends rounding our your healthy diet with 10 percent to 35 percent of your calories from protein; Harvard Medical School notes that higher protein diets have an advantage for weight loss because they are more satiating. However, eating the wrong type of protein can increase your risk of heart disease and diabetes. Avoid high-fat red meats and processed meats such as bacon and hot dogs, and instead get your protein from nuts, beans, fish and poultry. According to Harvard, people who eat more red and processed meat are more likely to gain weight, while those who eat nuts tend to gain less weight.
It's not just about what food you eat to avoid obesity but also about eating the right amount of it. After all, preventing weight gain is mainly about keeping a caloric balance by consuming the same number of calories as you burn. Portion sizes -- both at home and away from home -- have increased since the 1970s, says Harvard Medical School, and those who are served larger portions tend to eat more. To prevent obesity, learn what the proper portion size is for each food group -- it's different than the serving size listed on the product packaging -- and weigh or measure food to prevent overeating, if necessary.