OVER the course of a year, Alex Feintuch, a 20-year-old sophomore at the University of South Carolina, spent more than $1,000 on fitness supplements.

Mr. Feintuch wanted to add size and definition to his muscles, and to “see results as quickly as possible.” He did research and tried dozens of products, with mixed results.

“Of the products that I have bought, I’ve found many that work well,” he said. “But some don’t and were a waste of money.”

The fitness supplements industry is primarily aimed at young men like Mr. Feintuch. Bodybuilding-related products — powders and pills with names like Muscle Milk, Amplified Mass XXX and N.O.-Xplode — represented a $2.7 billion industry in 2008, but one whose benefits are in serious dispute.

The products are a subset of the more-familiar category of nutritional supplements, which includes mainstream items like vitamin-infused waters and energy bars. That market represented $25 billion in revenue in 2008, according to Nutrition Business Journal, a trade publication.

Athletes seeking peak performance are often concerned about eating right, choosing foods that allow their bodies to function at their best — everything from bananas to Peak bars. But going the next step to taking a pill or powder elicits more skepticism. Young female athletes, for example, are more apt to stick with multivitamins, energy drinks and bars, doctors and trainers say.

Male-oriented fitness supplements are not hard to find, but they are hard to figure out. Top-selling products like creatine, whey powder and nitric oxide are widely available under many brand names at drugstores and chains like G.N.C., but they are also minimally regulated, with a majority going untested by the Food and Drug Administration.

And that, sports medicine doctors say, points to the problems: there is little or no uniformity among products, the labels are confusing and the ingredients are arcane. Often, the main active ingredient is simply caffeine.

“It’s frustrating to not know exactly what I am putting in my body,” said Mr. Feintuch, who used a personal — and expensive — trial-and-error approach to come up with three products that seemed to work for him.

Doctors and nutritionists say that people who eat a normal diet generally don’t need nutritional supplements, even if they exercise vigorously. But among the subset of people who already eat healthfully and want to bulk up in the gym, some supplements, when taken in sensible doses, can provide a lift.

For instance, whey protein and creatine, which are meant to add bulk to muscles and raise the body’s ability to lift heavier weights, can, in some cases, help dedicated athletes become stronger faster, doctors and trainers say.

But the dose recommended on the bottle may be much higher than the dose recommended by doctors. And for this reason and others, doctors emphasize that only adults should take fitness supplements (although high school athletes often do). A policy statement by the American Academy of Pediatrics advises children under 18 to avoid them.

“Schools and other sports organizations should be proactive in discouraging the use of performance-enhancing substances,” said Dr. Teri M. McCambridge, who practices pediatric sports medicine in Towson, Md., and is the chairwoman of the American Academy of Pediatrics’ Council on Sports Medicine and Fitness.

Dr. McCambridge distinguishes between whey protein, which she considers to be a dietary supplement, and performance-enhancing substances like creatine and nitric oxide. Even so, she said, “the teenage diet already has more than enough protein.”

“They don’t need the extra amount” that a whey protein powder would provide, she said.

Further, most high school students “don’t know the importance of a recommended dose,” she said, and “there is a slippery slope when it comes to using other performance-enhancing drugs, like anabolic steroids and human growth hormone.”

And taking more than the recommended doses of fitness supplements can be harmful. Too much creatine in the system can lead to stomach upset and muscle cramps, among other things. And most people are familiar with the side effects of too much caffeine.

Jose Antonio, who edits a magazine called Sports Nutrition Insider and leads a nonprofit group called the International Society for Sports Nutrition, divides the popular supplements into three main categories: amino acid-based products, like whey protein and creatine; caffeine-based stimulants, and healthy fats like omega-3 acids.

Dr. Antonio is a proponent of several supplements, including whey protein and creatine, but says an athlete’s goals should determine his or her “strategy for use.” Creatine helps add size quickly, so it is good for people who want to bulk up, he said. Whey protein is more of a general fitness supplement and helps hasten the recovery of muscles after a workout, he said.

Some personal trainers recommend nutritional supplements to their clients. “If you’re looking to bust through a plateau, taking five grams of creatine before your workout might help you do that,” said Steve Hoffman, a trainer in Cherry Hill, N.J. “It adds water weight to your muscle and helps you lift more.”

For clients who want to intensify their workouts, Mr. Hoffman recommends products with arginine (an amino acid) or caffeine. He has experimented with such products and researched their effects, but he recommends caution for people who have not. “They’re awesome for working out — just be careful,” he said.

via Fitness – Fitness Supplements – When the Gym Isn’t Enough – NYTimes.com.