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 — …

When Dan Gerkey was trying to get into better shape a few years ago, he tried out a dietary supplement from a local store that promised to help build his strength. At first, the stuff worked. But after several weeks the police officer, who lives in Fraser, Mich., started feeling exhausted, and his wife noticed a yellowish tinge in his eyes.
Soon, Mr. Gerkey’s skin also yellowed, and it itched so fiercely that taking a shower or pulling on his socks became agonizing. Eventually, a liver specialist at Henry Ford Health …