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Despite major gains in fighting hepatitis C and other chronic liver conditions, public-health officials are faced with a growing epidemic of liver disease that is tightly linked to the obesity crisis.

In the past two decades, the prevalence of the disease, known as nonalcoholic fatty liver, has more than doubled in teenagers and adolescents, and climbed at a similar rate in adults.

Studies based on federal surveys and diagnostic testing have found that it occurs in about 10 percent of children and at least 20 percent of adults in the United States, eclipsing the rate of any other chronic liver condition.

There are no drugs approved to treat the disease, and it is quickly becoming a leading cause of liver transplants nationwide.

Doctors say the disease, which causes the liver to swell with fat, is particularly striking because it is nearly identical to the liver damage that is seen in heavy drinkers. In this case, the damage is done not by alcohol but by poor diet and excess weight.

“The equivalent of this is foie gras,” said Dr. Joel Lavine, chief of pediatric gastroenterology, hepatology and nutrition at NewYork-Presbyterian Morgan Stanley Children’s Hospital. “You have to force-feed ducks to get fatty liver, but people seem to be able to develop it on their own.”

Gavin Owenby, 13, of Hiawassee, Ga., learned he had the disease two years ago after developing crippling abdominal pain. “It’s like you’re being stabbed in your stomach with a knife,” he said.

An ultrasound revealed his liver was enlarged and filled with fat. “His doctor said it was one of the worst cases she had seen,” said Owenby’s mother, Michele Owenby.

With no drugs to offer him, the doctor warned the boy that the only way to reverse his fatty liver was to exercise and change his diet.

“They told me to stay away from sugar and eat more fruits and vegetables,” Owenby said. “But it’s hard.”

Most patients have a less severe form of the disease, with no obvious symptoms. But having nonalcoholic fatty liver is a strong risk factor for developing heart disease and type 2 diabetes.

In 10 to 20 percent of patients, the fat that infiltrates the liver leads to inflammation and scarring that can slowly shut down the organ, setting the stage for cirrhosis, liver cancer and ultimately liver failure. Studies show that 2 to 3 percent of American adults, or at least 5 million people, have this more progressive form of the disease, known as nonalcoholic steatohepatitis, or NASH.

“This is the face of liver disease in the United States,” said Dr. Shahid Malik of the Center for Liver Diseases at the University of Pittsburgh Medical Center. “If you’re at any liver-transplant center in the country, there’s no doubt that this is a big problem.”

Three decades ago, NASH was so rare that there was no medical name for it. Many doctors assumed that fat that accumulated in the liver was fairly harmless.

But today, NASH is a growing strain on liver clinics and the fastest-rising cause of liver transplants.

A study by the Mayo Clinic found that the percentage of all transplants performed nationwide because of NASH had reached 10 percent by 2009, up from 1 percent in 2001, even as the rates for hepatitis C, alcoholic liver disease and other conditions remained stable.

NASH is projected to surpass hepatitis C as the leading cause of liver transplants by 2020, in part because of new drugs that can effectively cure hepatitis C, but also because of the rapid growth of fatty-liver disease.

Fatty liver strikes people of all races and ethnicities. But it is particularly widespread among Hispanics because they frequently carry a variant of a gene, PNPLA3, that drives the liver to aggressively produce and store triglycerides, a type of fat. The variant is at least twice as common in Hispanic Americans compared with African Americans and non-Hispanic whites.

In Los Angeles, liver disease is diagnosed in 1 out of 2 obese Hispanic children, and it is a leading cause of premature death in Hispanic adults.

At UCLA, home to one of the largest liver-transplant centers in the world, nearly 25 percent of all liver transplants are performed because of NASH, up from 3 percent in 2002.

If the prevalence of NASH continues to increase at its current rate and effective treatments are not found, about 25 million Americans will have the disease by 2025, and 5 million will need new livers, said Dr. Ronald Busuttil, chief of the division of liver transplantation at the David Geffen School of Medicine at UCLA.

“I’m really afraid that the explosion of this condition is going to overrun the resources available to the transplant centers around the country,” Busuttil said.

“In the United States right now, we do about 6,000 to 7,000 liver transplants a year. Can you imagine if we have millions of people on the list? It’s unfathomable.”