By JANE E. BRODY

he debate over high-fat versus low-fat as a means of weight control flared up again this summer, leaving many weight-conscious Americans thoroughly confused and most nutrition experts up in arms.

Though billed as a "diet revolution," the high-protein, high-fat, extremely low carbohydrate diet championed by Dr. Robert C. Atkins is hardly revolutionary. It was first promoted in the late 1800's by an English coffin maker and has reappeared periodically in various incarnations, most successfully since the early 1970's by Dr. Atkins, who promoted it with a series of books and a clinic that bear his name.

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Does it help people lose weight? Of course it does. If you cannot eat bread, bagels, cake, cookies, ice cream, candy, crackers, muffins, sugary soft drinks, pasta, rice, most fruits and many vegetables, you will almost certainly consume fewer calories. Any diet will result in weight loss if it eliminates calories that previously were overconsumed.

This diet seems easy because it places no limits on the amounts of meats, fats, eggs, cheese and the like you can eat. These foods digest slowly, making you feel satisfied longer. Also, a diet without carbohydrates causes the body to make substances called ketones that may create a mild nausea, suppressing hunger.

But in a major report last week, the Institute of Medicine of the National Academies emphasized the importance of balance of nutrients, with carbohydrates — starches and sugars — making up 45 percent to and 65 percent of daily calories and fats, 20 percent to 35 percent. The panel of 21 scientists also urged Americans to keep as low as possible their consumption of saturated fats, the foods Dr. Atkins recommends as his diet's main components.

Testimonials abound from people who have lost scores of pounds — painlessly, they say — on the Atkins diet. This is not surprising. After all, how much of a limited category of foods can you eat before you find yourself eating less and less? With few carbohydrates, the weight initially comes pouring off — literally — in body water, the first 5 to 10 pounds of weight loss.

One question I'd like to see answered is how long anyone can stay on such a scheme and what happens when you start adding back some of the wholesome foods limited or forbidden on this diet, like sweet corn, grapes, watermelons, potatoes, carrots, beets or oatmeal.

The Great Unknowns A more important question: For those who stick with the diet, which allows back very limited amounts of carbohydrate-rich foods, what happens to their health?

In a study by Dr. Chia-Ying Wang and colleagues at the University of Texas Southwestern Medical Center in Dallas, reported in August in The American Journal of Kidney Diseases, just six weeks of a low-carbohydrate, high-protein diet greatly increased the risk of developing kidney stones. "This study shows that this is not a healthy way to lose weight," Dr. Wang said.

What is surprising is that after three decades of simmering and soaring popularity, the Atkins diet has yet to be tested for long-term safety and effectiveness.

In an interview, Dr. Atkins said: "A long-term study would cost millions and millions of dollars. We can afford to do a six-month study." Those shorter studies, he said, have shown "major improvements in lab tests and well-being." He said his foundation has contributed to a study under way at Harvard comparing the short-term effectiveness and health effects of diets low in carbohydrates versus diets low in fat.

Dr. Abby Block, nutritionist at the foundation, said studies of the Atkins diet lasting six months to a year and extensive clinical experience, have shown consistent improvements in blood lipids and glucose levels, suggesting that the diet can improve health despite its high levels of saturated fats and cholesterol, long associated with heart disease risks.

Why hasn't the government tested it? One possible reason is that it is unlikely to be approved by any review committee, given what is known about the effects of animal fats and cholesterol on the risk of heart disease, strokes and some cancers, as well as accumulating evidence that diets rich in fruits and vegetables and moderate in protein and fat can prevent diseases like high blood pressure, prostate cancer, heart disease and diabetes.

The Atkins diet is shy on several vital nutrients, including the B vitamins and vitamins A, C and D, antioxidants that slow the effects of aging, and calcium. And, a diet rich in animal protein can draw calcium from the bones, increasing the risk of osteoporosis and hip fractures.

What Are the Facts?
 

The Atkins diet is attractive to many Americans who have found it hard to lose weight on a low-fat diet. In recent decades, as Americans have been admonished to eat less fat, levels of obesity continued to rise, a situation noted in a recent article in The New York Times Magazine by Gary Taubes, a science writer, who told me he had lost considerable weight on the Atkins diet.

But many well-established facts can explain what happened to the American figure without damning carbohydrates or blaming low-fat diets, per se.

First, Americans are simply eating more — an average of 400 calories a day more than they did decades ago. Four hundred calories times 365 days divided by 3,500 (the amount of calories in a pound of fat) equals 41.7 pounds gained in a year, all other things being equal.

Of course, the caloric increase did not happen overnight, but the gradual increase, with little or no increase in caloric output from physical activity, can easily explain the creeping obesity that is now approaching a gallop.

Second, portion sizes have ballooned. A double cheeseburger, jumbo fries and supersize soda may be a single meal at a restaurant, but they contain all the calories a person should consume in an entire day. In a recent survey by the American Institute for Cancer Research, two-thirds of diners said they ate all they were served — at one sitting — most or all of the time.

When nutrition experts began urging Americans to cut back on fats, many filled in by eating more carbohydrates — a lot more than anyone recommended. Food producers jumped on the bandwagon to produce low-fat snacks and desserts, and Americans went hog wild, eating as much of them as they wanted.

Many fat-free foods have as many calories, or nearly as many, as their original high-fat versions, since sugars and other carbohydrates replace the fat and reduce the loss of flavor.

Third, Americans are not eating a low-fat diet. Despite a decline in the percentage of fats in the American diet, most people still eat the same amount. As caloric intake rose, the percentage of fat calories dropped but the total amount did not. Americans are eating more of everything, especially refined carbohydrates, which are made from white flour and sugars, doing neither their health nor their waistlines any good.

Too many refined carbohydrates can raise blood levels of heart-damaging triglycerides and may increase the risk of diabetes as well as obesity. Neither is it wise to cut out all fats. The body needs fat to aid in the absorption of essential nutrients, fat enhances flavor and satiety, and some fats actually promote health.

These ideas are not new. Several years ago, I wrote that healthful dietary fats found in foods like avocados, nuts and fish belong in the diet, both for disease prevention and weight control. I quoted Dr. Margo Denke of Southwestern Medical Center: "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."

To which Dr. Alice H. Lichtenstein, professor of nutrition at Tufts University in Boston, added: "Reducing fat alone is no guarantee of weight loss. You must cut calories or increase physical activity."

Dr. Denke concurred: "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."