Does fast food cause weight gain and obesity? It all depends on how you order and eat it. When you're choosing from menus full of fatty foods and oversized portions, it’s easy to order the wrong offerings and consume too many calories. If you're relatively sedentary, you will gain weight. If you continue to eat the same foods at the same activity level, you run the risk of becoming obese.
An average diet to maintain body weight accommodates about 2,000 calories per day, divided among three meals. If one fast-food meal contributes half of that daily total, the rest of your diet may push you over the limit, and your body will store those calories as fat. While salads, bean burritos and plain oatmeal have 200 calories or less, dressing, guacamole and dried fruit increase calorie counts.
Higher-calorie orders are typical: A 16-oz. orange juice, egg and sausage biscuit sandwich and hash browns, for instance, totals 900 calories. A double-patty hamburger, large french fries and a 16-oz. cola meal exceeds 1,300 calories. This leaves little additional room in your diet for the rest of your daily calories and nutrition.
If you frequently eat fast foods, the calorie overload will be more extreme. While your body burns some calories in metabolic activity and everyday tasks, you may be unable to deplete the excess. People who regularly exceed their calorie limits and don’t exercise enough can easily gain weight. The U.S. Department of Health and Human Services reports that on average, you need two and a half hours of weekly exercise to maintain a proper body weight.
So, how much fast food can you eat without getting fat? You can offset occasional high-calorie meals by eating lower-calorie foods at other times or by exercising more. If you don’t take those precautions, however, you may put on fat and gain weight. A 2005 article in “The Lancet” reported that in a study of young-adult eating habits, those who ate two or more fast-food meals per week gained 10 pounds on average over 15 years.
When your body mass index reaches 30, your overweight condition is termed obesity. Depending on your eating patterns, this may occur when you're relatively young or when you're middle aged. Obesity that results from eating fast foods full of saturated fats, such as burgers and fries, can dramatically increase your risk of developing heart disease and type 2 diabetes.