Small changes - big results.

Mitchell Walker doesn't especially love oatmeal, but he eats it every day--instead of a high-fat cereal--because he's trying to reduce fat in his diet wherever he can.

During breaks from his sedentary job as a feature film animator, he burns off a few more calories. "I walk up and down a hilly street near work just about every day for 20 minutes," says Walker, 42, who lives in Los Angeles.

I also drink lots of water, about one and a half liters a day," he says. It gives him a feeling of fullness and helps in his weight-control efforts.

Walker has discovered what researchers wish the rest of us would start believing: Making small changes in diet and physical activity can make a difference.

Trouble is, many of us think big--way too big--when it comes to losing weight, working out, and eating better.

"Americans dichotomize," says Alicia Moag-Stahlberg, a Chicago dietitian and spokesperson for the American Dietetic Association. "It's all or none."

Once in major overhaul mode, we plot a dramatic self-improvement campaign with an impossible deadline. Why not lose 10 pounds, start exercising, and slash fat intake--all by month's end?

The problem with such ambition, of course, is the failure factor.

Now the growing number of experts who suggest less is more say that one small change leads to others. This slow, steady approach is considered a much more predictable route to long-term success in maintaining a healthy diet and a healthy weight, they say.

Several recent studies back up this approach. Among them:

* Walking at a moderately fast pace for 30 minutes three times a week can lower mildly elevated blood pressures, says Dr. Jeffrey L. Tanji, a University of California at Davis researcher who presented his findings recently at the Canadian Academy of Sports Medicine meeting.

* Losing as little as three pounds can start to reduce blood cholesterol, according to a review of studies published in the American Journal of Clinical Nutrition.

* Fitting in short exercise sessions --even three 10-minute sessions a day--can yield training effects similar to one 30-minute session, according to a study by Robert F. Debusk, M.D., and published in the American Journal of Cardiology.

Even the conservative guideline to keep weight loss at one or two pounds a week is overkill, according to G. Ken Goodrick, assistant professor of medicine at Baylor College of Medicine. "Give yourself [a goal of] 12 ounces a week, and don't weigh yourself more than once a month."

The briefest exercise session, whether it's the only activity or added to a more intense workout routine, can also help.

"Take whatever opportunity you have during the day to exercise," says Debusk, a cardiologist and professor of medicine at Stanford University School of Medicine. Even if the only chance for exercise is to climb stairs or walk from the parking lot to work, "it will still have effects on weight maintenance," Debusk says.

In his view no exercise session is too short. i would like to do a study, comparing seven five-minute bouts of exercise with one 35-minute bout. I suspect that there would be quite a comparable effect."

Rich St. Clair buys into that theory. Besides his five-day-a-week routine of lifting weights and running on a treadmill, the Los Angeles attorney takes advantage of a few minutes stuck in traffic to do his "gut flexes" to strengthen abdominals.

"If I can't do an hour exercise class or walk, I go for a power walk around the mall," says Barbara Schiffman of Burbank, California. "I make it into an exercise situation for the short tenn."

"You might not think walking once or twice a week will make a difference [in weight control]," adds Simone French, of the University of Minnesota. But if you maintain that activity for two years, she predicts weight maintenance will be less of a struggle.

"We feel bouts of exercise can be thought of as medication," says Tanji, who recommends exercise for patients with mildly elevated blood pressures. If you have high blood pressure, the amount of exercise needed to improve blood pressure is not the same quantity as needed to improve physical fitness. It's less." In his eight-week study of 10 men, blood pressures dropped 10 percent to 20 percent when they walked for a half hour three days a week at a three-mile-per-hour pace.

When clients tell Moag-Stahlberg that a short bout of exercise or a small diet change is a waste of time, she tells them: "Log it." After a week or so, she says, they'll see how one small change leads to others and--faster than they had believed--visible differences.

Kathleen Dobeny is a southern California-based freelance writer with a special interest in health.

[C]1995, Kathleen Dobeny. Distributed by Los Angeles Times Syndicate.