The key to weight loss is simple when you consume fewer calories than you use. Although this fundamental tenet of weight loss is simple, the execution is difficult. Once your know how many calories you use daily, you can then determine how many calories to eat to lose weight. Many factors affect your daily calorie requirement, including your height, weight, age, sex and activity level.
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To decide how much you should eat to lose weight, first determine the number of calories needed to maintain your current weight. Calculators are available on many websites; look for one that takes into account key factors that affect your calorie needs. Age, for example, affects the number of calories you use daily. A 5-foot-4-inch, 180-lb., 20-year-old woman with a sedentary lifestyle requires roughly 1,885 calories daily to maintain her weight. A similar 40-year-old woman requires approximately 1,770 calories daily because metabolic rate slows with age. Your activity level also influences your calorie requirement. A 5-foot-4-inch, 180-lb., 40-year-old woman who participates in moderate exercise three to five days per week boosts her daily maintenance calories to approximately 2,285 calories, a 29 percent increase over what she needs if sedentary.
To lose weight safely, the American Dietetic Association recommends that you set your daily intake at 500 to 1,000 calories below what you require to maintain your current weight. Consider the example of a 40-year-old, 5-foot-4-inch, 180-lb. woman who exercises moderately three to five days weekly. Given that she requires approximately 2,285 calories daily to maintain her current weight, her target calorie intake to lose weight is 1,285 to 1,785 calories daily. Keeping all other factors the same but changing the age to 20 years old, target calorie intake is 1,435 to 1,935 calories daily. Your expected weight loss if you set your daily intake at 500 calories below maintenance level is 1 lb. per week. With a 1,000-calorie deficit, you can expect average weight loss of 2 lb. weekly.
What to Eat
Weight loss programs commonly target restriction of either fats or carbohydrates to achieve reduced calorie intake. These strategies make sense considering that solid fats and added sugar account for approximately 35 percent of the calories in the average American diet, according to the "Dietary Guidelines for Americans 2010." The relative advantages and disadvantages of low-fat versus low-carbohydrate diets remain hotly debated. Both strategies can be successful if you follow the program. A low-carbohydrate diet may lead to more weight loss initially, primarily due to decreased total body water. Whatever diet you choose should include a sufficient variety of foods to ensure that your vitamin, mineral and protein needs are met.
Talk with your doctor about the best diet for you, especially if you have a preexisting medical condition such as diabetes, heart disease, liver disease, kidney disease or high blood pressure. Your doctor may recommend that you consult with a dietitian to develop an individualized weight loss plan that meets your nutritional and medical needs.
- BMRCalculator.org: BMR Calculator
- "Journal of the American Dietetic Association"; Position of the American Dietetic Association: Weight Management; February 2009
- "Dietary Guidelines for Americans 2010: Foods and Food Components to Reduce"; U.S. Department of Agriculture and U.S. Department of Health and Human Services; 2010
- American Dietetic Association: Back to Basics for Healthy Weight Loss