Several factors contribute to your weight, including total body water, muscle mass, body fat and organ and bone mass. You diet because you want to lose excess body fat. Depending on how you go about losing weight, however, you may end up losing pounds that do not represent a significant reduction in your total body fat.
Energy and Weight Loss
Food is fuel, which your body burns to generate the energy it needs to function. Your body can use sugars, fats and proteins for fuel. Calories are the energy currency of the human body. The higher the caloric content of a given food, the more energy your body can produce from it. When you eat, your body stores calories it doesn't need in the short term as fat. Think of fat as your body's energy savings account. If your caloric intake regularly exceeds the amount of energy you expend, the surplus causes weight gain because your fat stores grow. To lose body fat, you must use more calories than you consume. The energy deficit causes your body to burn stored fuels, leading to weight loss. When you are dieting, the amount of weight loss that represents a reduction in body fat depends on how many calories you consume, what types of foods you eat and your activity level.
Water Loss
It's exciting when you drop several pounds in the first few days of dieting. Although the weight loss is encouraging, it often represents primarily a reduction in body water. When you go on a diet, you usually eliminate salty snack foods, salad dressings and other sodium-rich foods. Depending on how much salt you were eating before you began your diet, the reduction in salt intake can lead to rapid loss of excess body water and shedding several pounds. Weight loss caused by reduced body water also commonly occurs if you go on a "crash" diet with severely restricted total calorie intake. In the first day or two, these diets cause you to burn stored sugar, or glycogen, which causes a reduction in total body water.
Protein Loss
When you have a calorie deficit, your body does not necessarily burn stored fat exclusively. Proteins may also be broken down to generate energy. Because your muscles contain a large amount protein, you may lose muscle mass while dieting. Significant protein loss is most likely with crash diets that limit your daily caloric intake to less than 50 percent of your maintenance needs. For example, if you need 2,100 calories daily to maintain your weight and are following a 1,000-calorie diet, you are likely to lose both muscle and fat. This is particularly true if you are not obese. If you are only a few pounds overweight, going on a crash diet can lead to protein loss from your organs, which may adversely affect your health.
Optimizing Fat Loss
Although rapid loss of body fat is the hope of all dieters, losing 1 to 2 lbs. per week is most likely to accomplish a reduction in body fat. Combining exercise with moderately reduced caloric intake is your best bet for losing body fat without a significant reduction in muscle mass. Including adequate amounts of protein in your diet plan also helps prevent muscle loss while dieting.
References
- The President's Council on Physical Fitness and Sports; Exercise and Weight Control; March 2011
- FamilyDoctor.org: What it Takes to Lose Weight
- Net Wellness: Obesity and Weight Management, Starvation Mode
- "Diabetes Spectrum"; The Physiology of Body Weight Regulation: Are We Too Efficient for Our Own Good?; Betsy B. Dokken, Ph.D., N.P., C.D.E., Tsu-Shuen Tsao, Ph.D.; July 2007
- U.S. Department of Health and Human Services; 2008 Physical Activity Guidelines for Americans; Active Adults; October 2008
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