But, as CBS News Correspondent Sharyl Attkisson reports, three years ago McDonald's military career came to a sudden halt. During physical training he collapsed. His heart stopped and rescuers shocked him back to life.
"I woke up in a hospital," he says.
He didn't even recognize his own wife.
"We laughed because he tapped his mother over his shoulder and said, 'Who's that pretty girl over there?' " his wife Margaret remembers.
Today, he can't recall his own wedding day, and sometimes can't remember from one minute to the next. McDonald's collapse mystified doctors, but they soon honed in on one factor.
"The only thing he was really taking was Ripped Fuel," says Margaret.
McDonald is now suing the makers of Ripped Fuel, one of dozens of dietary supplements containing the herb ephedra, a chemical cousin to speed. It's used to boost energy, build muscle or lose weight. Because it's all-natural, McDonald thought it was safe. But a growing chorus of critics claims ephedra is not safe.
Also called "Ma huang", ephedra is banned by the Olympics committee, the NFL and the NCAA. The U.S. military has recorded injuries and deaths in troops that took ephedra.
Yet it remains wildly popular. The industry brags three billion servings are consumed every year.
That frustrates Raymond Woosley, a pharmacologist hired by the FDA in 1995 to analyze a rash of deaths and heart problems in teenagers who'd taken ephedra.
"There's no doubt in my mind that these we're being caused by the ephedra products," Woosley says.
After reporting his findings to the FDA, Woosley thought the agency would move quickly to restrict ephedra. But that didn't happen.
Part of the problem is that herbal supplements are officially classified as a food and not a drug - meaning they don't have to be proven safe or screened by the FDA before they're put on the market. And the proof required to force them off the market is much higher than what's necessary to ban a dangerous drug.
The ephedra industry says its own scientific studies show the herb is completely safe.
"Consumers should understand that if there were any science indicating that the products were doing what some of the critics claim they're doing, that the industry would pull these products off the market in a heartbeat," says Wes Siegner, of the Ephedra Education Council.
In 2000, the FDA again tapped Woosley to review 135 more cases, this time mostly young women and athletes.
"We saw the same thing," he says. "People were dying. People were having heart attacks, strokes that (they) shouldn't have."
Despite the second analysis, the FDA failed to act, in part, Woosley says, under pressure from the powerful ephedra industry. Now, the watchdog group Public Citizen is demanding the FDA ban ephedra. The FDA has put off a decision until at least fall 2002.
No matter what the outcome, McDonald blames ephedra for grounding him from the career he's dreamed of since he was a kid.
McDonald says he will never fly again in the military.
"My military career was cut short," he says.
Ironically cut short, he believes, by an herbal supplement he thought would give him an edge.