This is an excerpt from Athlete's Guide to Making Weight, The by Michele Macedonio & Marie Dunford.
Nutrition experts weigh in on water weight
Athletes who need to have their weight certified often ask whether they can safely manipulate food and water intake in the 24 hours before weigh-in. The diet-related strategies commonly used are restricting sodium, food, or fluid intake one or two days before weigh-in or a bodybuilding contest.
Any practice employed to cut weight may be unsafe, but temporarily restricting sodium intake is the least likely of the three to cause serious harm to performance and health. Sodium is associated with water retention. When sodium is consumed in food nearly 100 percent of the sodium is absorbed. Water will also be temporarily retained until the body can reestablish sodium and water balance by excreting excess sodium and water in the urine.
When sodium is temporarily increased in the blood, which may occur after consumption of a salty food or meal, water is pulled into the blood from the cells. Blood volume temporarily increases, the cells become slightly dehydrated, and a complex hormonal response eventually drives the person to drink more fluid. Fluid intake offsets the temporary increase in blood sodium and restores water balance. Similarly, a decrease in blood sodium decreases the amount of water in the blood, but blood sodium can decrease only slightly before the risk of heat illness increases.
Restricting dietary sodium can result in loss of body water through urine as the body tries to reestablish sodium and water balance. Reducing sodium intake to very low amounts (for example, 1,000 to 1,500 milligrams daily) would likely result in a loss of about 600 milliliters (2.5 cups) of water on the first day or about 1.25 pounds (.57 kilogram) of scale weight. Over a seven-day period the total loss of water weight from substantial sodium reduction is likely to be about 3 pounds (1.4 kilograms).
Note that a 1,000 to 1,500 milligram sodium diet is extremely low in sodium. Thus, many familiar and convenient foods usually consumed would have to be temporarily excluded. Eating in fast-food outlets or other restaurants would be difficult. As a short-term strategy, reducing sodium intake to very low amounts can result in a temporary loss of fluid and a loss of 1 to 3 pounds (.45 to 1.4 kilograms) of water weight. The short-term restriction of sodium is not likely to affect health negatively because the body has a large reserve of sodium in bones. But sodium restriction is not useful as a long-term strategy to lose body fat.
Restricting food intake one to two days before weigh-in is a short-term starvation state to which the body can adapt. A few immediate health problems are likely to occur, such as headaches, irritability, light-headedness, and a reduced ability to concentrate. Substantial performance-related problems can develop, including the depletion of liver and muscle glycogen and the breakdown of muscle protein. A 24- or 48-hour fast might result in a loss of 1 to 3 pounds (0.45 to 1.4 kilograms) of weight (depending on body size), but about two-thirds of the weight lost will be water, glycogen, and protein.
Restricting water intake, even for a day or two, is a dangerous practice and is not recommended. Water restriction is particularly harmful to the tissues that contain a large proportion of water. Blood is about 90 percent water, and muscle and organs typically contain 70 to 80 percent water. One cup of water weighs about 240 grams, or 0.5 pound. When water is restricted the body compensates by reducing the amount of urine excreted, so water restriction is not likely to produce a large loss of scale weight. But it immediately affects blood, muscle, and organ function and has the potential to damage the kidneys.
Athletes who choose to reduce water weight before weigh-in should begin fluid consumption immediately after weight is certified. The amount of fluid that a person can tolerate will vary, but the goal is to get as close as possible to 100 percent restoration of hydration. The degree to which dehydration can be reversed depends on the length of time until competition, which may be as short as one to two hours. Some ways to tell whether hydration status is improving include greater urine volume, lighter urine color, and less thirst.
If the intake of food and water is restricted before weigh-in, consume a carbohydrate containing beverage as soon as your weight is certified. Such a beverage helps restore fluid balance, replenish muscle and liver glycogen, and increase blood sugar level, which will help you feel more energetic.