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Weight cutting is the practice of rapid weight loss prior to a sporting competition. It most frequently happens in order to qualify for a lower weight class (usually in combat sports, where weight is a significant advantage) or in sports where it is advantageous to weigh as little as possible (most notably equestrian sports). There are two types of weight cutting: One method is to lose weight in the form of fat and muscle in the weeks prior to an event; the other is to lose weight in the form of water in the final days before competition.
Nutritional experts will rarely give advice on how to cut weight safely or effectively, and will simply recommend against cutting weight at all. However, many athletes choose to do it because they wish to gain an advantage in their sport.
In addition to improving performance through healthy eating, some athletes will seek to lose weight through dieting and aerobic exercise. By losing fat they hope to achieve a higher "strength to mass ratio" or "lean weight." This means more muscle and less fat, and should theoretically give them an advantage against other athletes of the same weight.
Healthy weight loss can be seen as a positive effect of participation in sports, but reducing body fat too greatly can cause health problems. Athletes should try to maintain their body fat at the lowest healthy level to achieve their best performance.
Athletes at the elite level will sometimes attempt to temporarily lower their body fat to unhealthy levels to give themselves an edge in important competitions. Afterwards they will regain the lost fat, and return to their normal training weight. This technique should not be attempted without knowledge of periodization and the help of a knowledgeable coach and medical advice.
Children and teenagers should be cautioned to avoid losing weight at excessive quick rates or to excessively low levels the way adult athletes may choose to. Young bodies require additional nutrients to grow. Weight-cutting techniques can interfere with healthy physical development.
Athletes use a number of different supplements to stimulate fat loss. Green tea has been shown to increase the metabolic rate by a small amount. Conjugated linoleic acid (CLA), found in beef, lamb, milk, and cheese, is theorized to reduce body fat in individuals who exercise.
Muscle loss 
Although it may be extremely difficult, it is possible to retain muscle while losing fat.
Some athletes desiring rapid weight loss may choose to sacrifice muscle mass by eating a low protein diet. However, most athletes are interested in maximizing fat loss while minimizing muscle loss.
The best way to minimize muscle loss while losing weight is through resistance training. If emphasis is being placed on aerobic training, resistance training will be a smaller part of the athlete's training program, promoting greater muscle loss. Muscle growth cannot be expected unless emphasis is placed on resistance training, but muscle loss can at least be slowed. After a period of weight loss, athletes may wish to do a period of weight training to recover lost muscle.
The athlete should remember to eat protein at all meals, especially before aerobic exercise. This will help slow muscle loss. Some athletes may choose to use supplements to minimize muscle loss; Glutamine is a popular choice.
About 65% of the human body is made of water under normal conditions. This makes it tempting for athletes to temporarily lose weight through dehydration prior to weigh-ins. This weight can then be rapidly regained immediately afterwards.
A good rule of thumb for most athletes is to lose no more than 5% of their total body weight through dehydration. Athletes at an elite level often lose more than this. It should not be attempted without a knowledgeable coach and medical supervision.
Immediately before weigh-ins, athletes can put on warm clothes and engage in aerobic exercise to make themselves sweat. Garbage bags can be worn against the skin to eliminate cooling through sweat evaporation.
Some athletes choose to sit in a sauna so that they can sweat without wasting energy. Another technique is to chew gum to induce salivation, then to spit out the saliva instead of swallowing it.
Athletes should remember to urinate and defecate as this is an easy way to reduce weight. Some athletes may choose to take diuretics and laxatives to aid in this. Some diuretics are banned by the WADA in events such as the Olympics as they mask Steroid detection in post drug tests, some may also have harmful effects on the body.
Losing weight through dehydration is not recommended, as it may lead to decreased performance, and, more importantly, serious injury.
After weigh-ins, athletes should immediately begin rehydration. Some sporting events hold weigh-ins on the day before competition; others hold weigh-ins on the same day, only hours before competition. This is often done to discourage excessive weight cutting.
Athletes should continuously sip liquid containing carbs, protein, and sodium until they compete. Many athletes are told not to eat too much food all at once for this will lead to upset stomach. A small amount of food can be eaten once every hour before competition, and no later than 3 hours before an event starts. Rehydration cannot be achieved in a single sitting, as the body can only be rehydrated at a rate of 1.5 litres per hour (3.3 lb/h).
The best drink for rehydration is not pure water. The body requires electrolytes in order to retain water. An oral rehydration solution is the best choice. Sports drinks also work, but contain excessive sugar that may negatively affect performance. Another possible choice is vegetable juices and water. A popular rehydration drink among athletes is Pedialyte, due to its low sugar levels.
See also 
- Human weight
- Weight loss
- Eating disorder
- Healthy eating
- Aerobic exercise
- Strength training
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