Their message: In moderation, fat is essential. In fact, low-fat diets can not only harm the performance of certain athletes, they can place the athletes at a considerable health risk.

The State University of New York at Buffalo leads the way in the research, with several studies concluding that low-fat diets can be dangerous.

"We've been doing work with athletes all the way from modern dancers to soccer players to long-distance runners. What we've basically been finding is that there is a negative aspect to a very low-fat diet -- below the recommended 30 percent of calories," says Peter Horvath, an associate professor of nutrition.

Fat is a fuel source. It helps athletes who expend high amounts of energy to maintain strength and stamina. And both the immune system and the heart and blood vessels can be harmed by not enough fat in the diet, Horvath says.

"Especially in long-distance runners, when we've examined their diets and found them to be anywhere between 10 and 20 percent dietary fat, we've found that it compromises their immune response and, cardiovascularly, they actually lose the benefit of the exercise," he says.

In the study of the immune system, researchers took blood samples of the athletes and examined them in a laboratory to see their response to immune challenges.

A weakened immune system

"In a low-fat diet, the cells were less able to mount a defense. Some of those immune cells prefer fat as a fuel," Horvath notes.

Low-fat diets can also have a negative effect on both good cholesterol -- HDL -- and bad cholesterol -- LDL -- triggering the cardiovascular problems, he adds.

Horvath says elevating low-fat diets from the 20 percent range to 30 percent or higher increased HDL, lowered LDL and improved athletic performance -- not only for elite athletes, but for weekend athletes as well.

One Buffalo study of recreational runners with low-fat diets increased both the fat intake and caloric consumption of the athletes. The result, according to Horvath, was that "they ran about a 12 percent increase in distance when they went up to a higher fat level."

Sports nutritionist Nancy Clark agrees that low fat can mean low performance for athletes.

"What I look at is when athletes have very little fat in their diets, they often have very little protein along with very little iron and zinc. So by eliminating fat, you eliminate other factors and compromise your ability to perform," she says.

The 25 percent solution

Clark says 25 percent of calories from fat is a good goal for almost everyone.

"The average American is getting 34 to 37 percent of his calories from fat. The American Heart Association recommends 30 percent and if you have heart disease, you talk about 20 percent. So 25 percent is a low-fat, health-conscious target," she says.

Clark, who had written books on sports nutrition, says she counsels her athletes to get their fats from healthy sources, such as nuts, fish or olive oil.

Another fat-conscious observer is Bob Williams. He's coached athletes for 34 years in the Portland, Ore., area. A former All-America steeplechaser at the University of Oregon, he competed in the U.S. Olympic trials in 1968 and 1972.

"What I try to do is to make sure that the athletes I coach are eating a healthy, balanced diet with carbohydrates, fats and proteins," he says.

But when he tries to get a little more fat in the marathon runners he coaches, this advice is often met with some resistance. "There are some athletes who are just anal-retentive about what they put in their mouths," he says.

"I tell them food should be a friend. It should be something that you rejoice with and I try to get people to splurge every once in a while. I give them permission to eat sensibly and they mostly respond in a very positive way," he says.

The University at Buffalo's Horvath says athletes and nonathletes alike need to change their ways of thinking about a healthy diet.

"You want to aim at 30 percent of your calories from fat," he says. "But worry about caloric intake. That's where things are going back to in terms of health."

What To Do

Don't trim fat completely. It's required to help you absorb fat-soluble vitamins (A, D, E and K), and some is needed because your body can't make essential fatty acids.

According to the Mayo Clinic, a tablespoon of vegetable oil meets the daily requirements of most normal people. Children need more fat. Fat is high in calories (and essential fatty acids) and is necessary to support a child's rapid growth and development. This is why a low-fat diet is not advised for children under 2 years.

This HealthSCOUT story reports on one study that found that a diet high in monounsaturated fats reduced the risk of cardiovascular disease by 20 percent.