LOS ANGELES — Five years ago, flyweight boxing champ Nonito Donaire felt as if his body had shrunk as he dieted to make the 112-pound weight limit to defend his title.

Blood was in his urine before the bout, Donaire recalled.

“Everything about you is not there,” he said. “You feel like an animal.”

Donaire won that bout, but he later moved up in weight to avoid such trauma. This month he fights in a super-bantamweight title unification bout in nearby Carson against Toshiaki Nishioka at a more comfortable 122-pound limit.

Making weight is a fighter’s duty — and it’s often a challenge.

In the last year world champion boxers Brandon Rios and Adrien Broner both failed to make weight for their bouts, and an Ultimate Fighting Championship contender dropped at least 17 pounds in the day before his title shot. Medical experts and regulators question the inexact methods behind sudden weight loss and say it requires more oversight and education.

“It’s a medical crisis,” said Dr. Paul Wallace, a California State Athletic Commission ringside doctor. “There’s not a credible diet that says you can lose 10 percent of your weight in a month, much less one day.

“But it’s not a sport crisis because people have seen boxers like Fernando Vargas, Roberto Duran, Ricky Hatton take off massive weight, still come back and give a good fight and ask, ‘How bad can it be?’”

Weigh-ins are usually 24 hours before a bout, so fighters have time to step on the scales, then eat and drink their way closer toward full strength and their normal weight by fight time. As a result, some fighters have a huge weight advantage when they step into the ring.

Last February Julio Cesar Chavez Jr. made the middleweight limit of 160 pounds, with half a pound to spare, for his World Boxing Council title defense against Marco Antonio Rubio. On fight night Chavez reportedly weighed closer to 180 when he won a lopsided decision over Rubio.

The WBC is now considering implementing fines against fighters who suddenly pack on too much weight after a weigh-in. In addition to the current required 30-day and seven-day weigh-ins before fights, the WBC might slap fines on any fighter who adds more than 5 percent of his body weight between the final weigh-in and fight night.

Beverly Hills internist Dr. Robert Huizenga, a former NFL team doctor, said even top fighters don’t have a grasp of the effects of cutting weight. He cites Oscar De La Hoya’s sluggish effort in his final fight, when he quit after eight rounds against Manny Pacquiao. De La Hoya weighed in for that bout at 145 pounds after fighting a year before at 154 pounds.

When a fighter rids the body of too much salt, Huizenga said, they risk a possibly fatal condition known as hyponatremia. And cutting weight can leave fighters prone to absorbing excessive punishment and brain trauma in the ring. “There’s technology to analyze if an individual is too dehydrated,” he said. “There should be a rule that those too dehydrated at the weigh-in shouldn’t fight.”