CUTTING OUT ALL FAT NOT SO GOOD IDEA.

Byline: Jane E. Brody The New York Times

Now hear this: Avocados, walnuts, salad dressings with oil, sauteed vegetables, fatty fish and some kinds of margarine may be back on the menu for health-conscious Americans, even for those trying to lose weight, if the findings of recent studies are to be believed.

For three decades now, Americans have been bombarded with advice to eat less fat for the sake of their hearts and their waistlines. One well-known expert, Dr. Dean Ornish, advocates stripping away all added fats and naturally fatty foods to achieve a diet containing no more than 10 percent of calories from fat, down from the 44 percent typically consumed by Americans in the 1960s and the 34 percent now consumed.

But now a growing number of nutrition, health and obesity specialists maintain that in trying to squeeze some of the heart-damaging grease from our high-fat diets, they have sent Americans the wrong message.

It's not fat per se that's the problem, the experts now say, but the kinds of fats Americans eat and the other kinds of foods they fill up on when they cut back on appetite-satisfying fat. For while heart disease has indeed declined as many Americans shun artery-clogging saturated fats and cholesterol, waistlines have expanded significantly and obesity has risen by 50 percent since the big push to limit fat took off in the 1970s.

The very tactic viewed as the key to weight control - stripping the diet of fat - seems to have backfired. Food companies responded to fat phobia with a plethora of fat-free, low-fat and reduced-fat products, especially the dessert and snack foods that Americans covet.

The result was an overdose of carbohydrates, ranging from fat-free pretzels, crackers, cookies, cakes and frozen desserts to dinner plates piled high with pasta.

Many obesity specialists, as well as popular diet advocates like Dr. Robert Atkins and Barry Sears, say these carbohydrates are the cause of the growing American girth. Even the potato, which once proclaimed ``I am not fattening'' in award-winning ads, now heads the hit list being circulated by carbohydrate bashers, some of whom, like Atkins, go to the opposite extreme by recommending that people can lose weight by eating all the fat they want as long as they eat few or no carbohydrates.

``The swing back to Atkins is a response to the fact that a low-fat diet hasn't worked for a lot of people because they stuff in carbohydrates,'' said Dr. Margo Denke, an associate professor of medicine and endocrinology at the University of Texas Southwestern Medical Center in Dallas.

Dr. Alice H. Lichtenstein, a professor of nutrition at Tufts University in Boston, agrees that ``the low-fat pendulum swung too far.''

``People assumed that if a food had no fat, they could eat as much of it as they wanted,'' she said. ``But many low-fat and fat-free products have nearly as many calories as their full-fat versions. Reducing fat alone is no guarantee of weight loss. You must cut calories or increase physical activity.''

Denke said, ``No matter what anyone tells you, it's calories that count. Carefully controlled metabolic studies show that it doesn't matter where extra calories come from. Eat more calories than you expend and you'll gain weight.''

And that is just what Americans have been doing: gaining weight on fat-free and low-fat foods consumed without regard to their caloric content. Instead of replacing some of the less desirable high-fat foods with nutrient-rich but low-calorie fruits and vegetables, they are filling up on foods loaded with added sugars and refined starches that have little to offer nutritionally besides calories, the experts lament.

``In making food choices, we must learn to eat foods that are nutritionally robust - fruits, vegetables, legumes,'' said Dr. Robert H. Eckel, chairman of the American Heart Association's nutrition committee and professor of medicine and physiology at the University of Colorado. ``There is strong evidence that these kinds of foods help to reduce disease, not just heart disease but also cancer, diabetes, hypertension and obesity.''