Weight cutting for competition - reducing body weight to compete in a lower weight class - is a reality for combat sports athletes (boxing, MMA, wrestling, judo) and some strength sports (powerlifting, weightlifting). Done poorly, it severely impairs competition performance and carries genuine health risks. Done strategically, it can provide a competitive advantage with minimal performance cost.
The foundation of safe weight cutting: compete at the weight class closest to your natural training weight. A well-fuelled, well-hydrated athlete competing 2-3kg above their natural weight class will perform significantly better than a dehydrated, glycogen-depleted athlete who cut 8-10kg. The competitive advantage of a size advantage within the class is often negated by the performance cost of the cut.
Safe pre-competition weight reduction (6-12 weeks out): dietary calorie restriction to reduce body fat gradually (0.5-1% of body weight per week) while maintaining protein intake and training intensity. The majority of weight reduction should come from fat loss, not dehydration. In the final days before weigh-in, modest fluid restriction and sodium manipulation can reduce 1-2% of body weight as water. Aggressive dehydration (sweat suits, diuretics) reduces power output, endurance, reaction time, and cognitive function - the risks often outweigh the competitive benefits. Rehydration between weigh-in and competition is critical: consume 1.5 times the fluid deficit with electrolytes, and restore glycogen with carbohydrate-rich foods in the available window.