After beginning a new diet and exercise program, many people experience a sudden drop in body weight, sometimes of more than five pounds in a week. This dramatic change is very encouraging, and motivates people to continue with their new lifestyle changes. However, after two or three weeks, weight loss generally slows down considerably to anywhere from one-half to two pounds of weight loss a week. The dramatic weight loss during the first week is usually a result of water loss.
Typically, diet plans involve reducing the amount of processed food you eat; these foods are often packed with sodium. Your kidneys excrete sodium in urine if it is not needed. However, if there is too much sodium for your kidneys to excrete, the sodium starts to accumulate in your blood, causing you to hold water. When you replace the processed foods with natural, unprocessed foods and increase your water intake, your kidneys can begin to flush out the excess sodium and water weight that accompanies it, resulting in a sudden loss of water weight.
Carbohyrates and Water Weight
Diets low in carbohydrates can result in a sudden decrease in water weight during the initial stages of weight loss, because water storage accompanies carbohydrate storage. For every gram of carbohydrate used by the body, approximately 2.6 grams of water is lost, according to Jack H. Wilmore and David L. Costil, authors of "Physiology of Sport and Exercise." A complete depletion of carbohydrate stores could result in a four- to five-pound weight loss.
Fat loss occurs as a result of burning more calories than you take in. One pound of body fat is equivalent to 3,500 calories. A one- to two-pound fat loss in a week would require a 500- to 1,000-calorie deficit a day. Losing more than two pounds in a week usually means that you are losing water weight and lean muscle mass instead of losing excess fat, and you will most likely gain it back.
The most effective way to lose fat weight is to decrease caloric intake by 250 to 500 calories a day and to burn 250 to 500 calories a day through exercise and physical activity. Avoid fad or crash dieting, since most will just result in water loss and will be gained back as soon as your regular diet is resumed. Instead, regularly consume a well-balanced diet consisting of lean protein, whole grains, fruits, vegetables, low-fat dairy and unsaturated fat sources. Limit sodium intake to under 2,300 milligrams per day.