Never mind what the bathroom scale shows. The buzzword in evaluating fitness these days is body-fat percentage - the amount of fat in our bodies relative to our weight.
Body-fat percentage tests are among the most popular voluntary exams at health fairs and gyms, said Judi Ulrey, owner of Fitness Consulting in Costa Mesa, Calif., which conducts fitness tests.
Many people who take the test are consumed by their appearance, Ulrey said. Others believe reducing the percentage of body fat improves their level of fitness, said Joan Hackett, exercise physiologist and director of fitness programs at Shiley Sports and Health Center in La Jolla, Calif.
To maintain life, a person needs at least 3 percent to 5 percent body fat, fitness experts say.
For optimum health and fitness, widely used standards in fitness circles place the ideal percentage at 15 percent to 19 percent for men and 20 percent to 29 percent for women, Hackett said. Women tend to store more fat for reproductive reasons, she said.
But people who aren't into serious athletic competition shouldn't be so concerned about body fat or weight, some exercise physiologists say.
Less body fat doesn't mean fit - or healthy, according to Glenn Gaesser, associate professor of exercise physiology at the University of Virginia, in his new book, "Big Fat Lies: The Truth about Your Weight and Your Health" (Fawcett, $23).
People should be more concerned about the placement of that body fat and balancing daily exercise with sensible nutritional habits, Gaesser said.
"We should be more concerned about the fat in our diet than the fat in our bodies," he said. "The objective is that we should limit the amount of fat in our nutrition to no more than 20 percent of the total calories we consume and that we should have 20 minutes of moderate exercise every day."
Being thin isn't the key; it's being fit.
A thin person who looks lean can score high in a body-fat percentage test if he or she has very little muscle, said Jeff Dilts, exercise physiologist and fitness director at Sports Club Irvine. Gaesser has a name for someone like that: a thin fat person.
The perception that less body fat is better persists. "We tend to be a society with a preoccupation with fashion-model images," said Arthur Weltman, director of exercise physiology at the University of Virginia.
Extremely low body fat, in fact, can be detrimental to health and fitness. For most women, 11 percent body fat or less is medically unsafe. For most men, 5 percent or less is medically unsafe, according to the Biosyn Technical Manual, by Barry Sears.
One of the immediate effects of extremely low body fat is a great susceptibility to illness, Hackett said.
"Body-fat levels affect the immune system," she said. "It's not unusual for a triathlete or a marathoner two weeks before competition to get sick or catch a cold."
Over the long haul, very low levels of body fat can lead to loss of bone density, which increases the risk of stress fractures, Hackett said.
Women's reproductive cycles can be disrupted or stop entirely, she said.
People should be less concerned about the amount of fat and more concerned about its type and location, Gaesser said. Recent studies indicate that some body fat is good, and some is not.
"Most of our fat - somewhere between 70 and 80 percent for men, and more for women - is subcutaneous; that is, right beneath the skin," Gaesser said. That's the good body fat.
The bad stuff is the deep body fat, also called intra-abdominal or visceral fat, most of it in the abdomen around our internal organs, he said. A lot of deep body fat can give a person an apple shape, and it "seems to be associated with all health problems on which fat seems to have any bearing. . . . The more visceral fat you have, the higher the level of free fatty acids in your blood." He added that not all people who have the apple shape necessarily have a lot of visceral fat - some people may store a lot of subcutaneous fat in the midsection.
"Some of the bad body fat, released into the bloodstream, can clog arteries," Gaesser said. "And because visceral fat is so near the liver, a lot of the fatty acids it releases go directly into that organ, which may be impaired by too-high fat levels in the bloodstream."
Genes, gender - men have about twice the amount of bad fat as women - and lifestyle determine the amount and type of body fat. And lifestyle is the only factor we should be concerned about, because it's the only one people can control - with physical activity and sensible nutrition, Gaesser said.
In the context of fitness, people need to balance lean muscle mass with fat, exercise physiologists say.
"Generally, muscle and fat combined account for about well over half a person's weight," Gaesser said. "Men's bodies typically have a higher ratio of muscle to fat than women's bodies do."
The number and size of muscle and fat cells determine the amount of muscle and fat tissue and, consequently, a person's weight, according to Gaesser. Someone with a great number of large-size muscle and/or fat cells will weigh more than someone with fewer, smaller cells.
The number of muscle cells is determined before birth and remains the same for most of our lives, with some decrease in our senior years, Gaesser said. The size of these cells increases naturally as a person ages, but the size also can be increased with intense physical activity such as weightlifting.
Fat cells are a different story. People are born with a given number of fat cells, somewhere between 5 billion and 10 billion. This number increases with age: to roughly 20 billion for a lean person, and to 100 billion or more in a very fat person, Gaesser said.
These realities aside, many people obsess about decreasing body fat, sometimes setting themselves up for failure by comparing themselves to athletes.
The low-fat bodies of many successful athletes - including most swimmers, gymnasts, runners and beach-volleyball players - tend to be perceived as temples of perfection.
When swimmer Tom Dolan competed and won the gold at the last Olympics, the media mentioned that the 6-foot-6, 180-pound swimmer had only 3 percent body fat, a number most health experts deem medically unsafe.
Dolan has always been thin, but that number is questionable, according to Jaci VanHeest, director of exercise physiology for the U.S. swimming team. She estimates Dolan's body fat to be closer to 5 percent to 9 percent. "It gets dangerous when you start getting below 5 percent, even for a male elite athlete," VanHeest said.
There's no question that body-fat percentage is one of several statistics used by competitive athletes in monitoring fitness, although it is not the sole criterion, fitness experts say.
"For many types of athletes, it's important because too much fat tissue is really dead weight and doesn't contribute to performance," said Weltman of the University of Virginia.
But it's crucial for people to realize that body-fat percentage is just one small component of an athlete's total training program. Athletes burn a lot of fat and calories in training six to eight hours a day, VanHeest said.
What's more, 80 percent of the way a person's body looks - including fat percentage - is genetically determined, Hackett said. "Athletes are born, not made," she said.
And sometimes, even the most perfect-looking athletic bodies are the result of dangerous tooling. A competitive athlete's desire to decrease body fat can lead to eating disorders such as bulimia and anorexia, VanHeest said.
It's particularly notable among those aspiring to be elite athletes, she said. "Many will do anything to get there," VanHeest said. "A lot of them believe, just as the public does, that the leaner they are the better they will be, which is not necessarily true."