This is the sixth of eight stories in our Web feature on self-experimenters.

When Seth Roberts began suffering from insomnia in the early 1980s, waking up tired in the morning only to nod off again within a few hours, he could easily have taken sleeping pills for relief. But that would have deprived the Berkeley, Calif., experimental psychologist the satisfaction of spending the next decade trying to solve the problem himself.

Roberts, you see, is a die-hard experimentalist, and his favorite experimental subject is himself. For the past three decades, he has deliberately tinkered with his daily routine, slowly introducing one small change after another in his diet and other habits, all the while keeping careful track of the effects on his state of being—specifically, his weight, mood or sleep cycle. Although he hasn't convinced everyone that his methods are up to snuff, his bestselling book suggests someone is paying attention.

Roberts, 54, discovered his inner lab rat as a graduate student in psychology at Brown University in Providence, R.I., where he had to figure out how to design experiments on actual rodents. He found that practicing on himself was quick and easy, starting with his acne. By counting his blemishes daily, he discovered that a prescription cream cleared his complexion, allowing him to toss the antibiotics he had also been taking.

So began a life of systematic trial and error. To cure his insomnia, he tried exercise, calcium and adjusting the settings on fluorescent lamps near his bed. "I came to realize how ignorant I was," says Roberts, whose day job was studying rat learning at the University of California, Berkeley. On October 2, 1993, thinking that his choice of breakfast might play a role, he tried delaying his morning meal until 11 A.M. to get a baseline reading. Within a week the problem that had plagued him for years was gone. He resumed eating breakfast at 7 A.M. more than three months later, and his insomnia was back the next day.

A 2004 paper published in Behavioral and Brain Sciences set out the data behind the unexpected breakfast effect along with nine other findings from self-experiments. Among them: an hour of morning sunlight made his sleep even more restorative; so did being on his feet for nine hours a day. Watching faces on television talk shows early in the morning elevated his mood the following day—he guesses it reflects an ingrained response to social contact. (He has since switched to watching himself in the mirror, to see if any face will do.)

His weightiest finding, so to speak, was that he could regulate his appetite by drinking unflavored fructose water between meals. He dropped 35 pounds (16 kilograms) in this way from a starting weight of 185  (84 kilograms), then gained 10 of them back because friends said he looked gaunt. Later he found that a couple of tablespoons of flavorless vegetable oil worked equally well. Roberts put forth his theory of weight loss in a slim volume called The Shangri-La Diet, which cracked The New York Times Best Sellers list in 2006. On his Web site, he invites readers of his book to share what worked for them and what didn't.

Skeptics abound. Experimenters who test ideas on themselves may be biased to produce the result they expect to see, says David Katz, an internist and associate professor adjunct at Yale School of Public Health. The kind of self-experimentation that inspired Roberts's diet "doesn't reach the ground floor of evidence" for the general population, he says.

Whatever its limitations, Roberts, now professor emeritus at U.C. Berkeley and working on his second book, says self-experimentation is an easy way to generate new ideas. He sees nothing unusual in the practice. He's recently begun testing whether oils rich in omega-3 fatty acids (found in fish and eggs) improve his reaction time and balance [see image]. "Everybody makes these little tweaks in their life," he says. "The simplest, easiest thing will probably have something to teach you."

You might want to clear it with your doctor first, though.