The harms from rapid extreme weight cutting in combat sports (in order to then rapidly gain weight well above the weight class limit during competition) are well documented on this site.
How much weight do professional boxers regain following these cuts? A recently published study in The Physician and Sports Medicine journal sheds light on this.
The study, titled Rapid Weight Gain Following Weight Cutting in Male Professional Boxers, reviews data from the California State Athletic Commission between 2015-2018. It reveals’ that over 97% of athletes gain weight from weigh in to competition with over 20% of competitors ballooning up over 10% of their ‘official’ weight by the time they step in the ring. The full abstract reads as follows:
Weight classifications are used in boxing and other combat sports to match opponents of similar size. Professional boxers commonly engage in a potentially harmful practice known as rapid weight loss or “weight cutting” to make weight the day prior to competition before rehydrating and refueling. This investigation describes the prevalence and magnitude of rapid weight gain in boxers following weigh-in as well as differences in practice with respect to weight class and promotion.
This analysis describes official weight data from male professional boxers collected by the California State Athletic Commission between 2015 and 2018. A total of 399 athletes were included in the study.
Among included athletes, 389 (97.5%) athletes gained weight between official weigh-in and competition. Total absolute body mass gained was 4.4 ± 2.2 kg corresponding to a total relative body mass gain of 7.2 ± 3.5%. Boxers competing in international promotions gained significantly more body mass than regional competitors (8.0 ± 3.0% vs. 6.6 ± 3.7%; p<0.001). In total, 82 (20.6%) athletes gained 10% body mass or more before competition. More international competitors reached this 10% threshold than regional competitors (25.3% vs. 17.4%; p=0.03).
These findings indicate high prevalence and magnitude of RWG in professional boxing, particularly in boxers competing in elite international promotions.