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Confused by this week's news that a low-fat diet might not help prevent cancer and heart disease after all?

Beth Hobson was.

"I've been on a low-fat diet for four years now," said the 44-year-old part-time worker at a fitness center in Pasadena. "Does that mean I can go back to eating full saturated fats? I should go home and eat a pizza tonight?"

By no means, scientists said yesterday.

The real culprits in our diets, they say, are the hardened fats in margarine and shortening, as well as saturated fats in meat.

And people seeking healthy lifestyles should look beyond eliminating fat and actively incorporate more fruit, vegetables, whole grains and exercise.

"It's all about balance in all ways," said Dr. Jacques Rossouw of the National Heart Lung and Blood Institute.

Nor should those who adjust their eating habits to prevent bad things from happening expect quick results. "The effects of a change in diet are going to take a long, long time," he said.

Rossouw was project director of a $415 million study in which 48,835 post-menopausal women ages 50 to 79 were assigned to eat either a low-fat diet or anything they wished.

Researchers following the women over eight years found no statistically significant differences between the two groups in rates of colon cancer, breast cancer, heart attack and stroke - all the things that doctors hoped a healthy diet would prevent.

The study in this week's issue of the Journal of the American Medical Association surprised and puzzled many consumers who are growing weary of shifting advice about food.

"Whenever I try to pursue some nutritional strategy, it seems that there's always some new study that comes out years later reversing it," said Betsy Boyd, a 32-year-old freelance writer from Baltimore who was lunching yesterday at Atwater's in Belvedere Square.

Don't give up, said Cheryl Anderson, a nutritional epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

"It would be absolutely a mistake to think that you can just eat what you want and you're going to be OK," said Anderson, who collaborated with Dr. Lawrence J. Appel, a Bloomberg colleague, on a JAMA editorial.

"If you're only watching total fats, you may miss the subtlety of what types of fats you're eating."

Like many other scientists, Anderson noted that the study was conceived before evidence emerged that two particular types of fat could be the chief dietary evils in heart disease.

One, trans fat, is created when hydrogen is added to vegetable oils that harden into margarine or shortening. Trans fats are often used in commercial baked goods such as doughnuts, pastries and cookies. They show up in french fries and fried chicken served by most fast-food chains.

The other, saturated fat, is usually solid at room temperature and comes mostly from animal sources in meat, poultry, and whole milk and whole milk cheeses. Saturated fats are also found in certain plant oils such as palm, palm kernel, coconut oils and cocoa butter.

Both types of fat contribute to elevated blood cholesterol levels and increase heart disease risk, research shows.

A strategy that simply cuts back on all dietary fats - as the women in the federal study did - ignores this distinction and other knowledge that experts say they've gained.

"Ten years ago, our mindset was to lower the fat - the lower the fat, the better. That clearly has changed," said Dr. Michael Miller, director of the Center for Preventative Cardiology at the University of Maryland Medical Center.

More recently, he said, "Our approach has been not to restrict [total] dietary fats, but to restrict saturated fats and to eliminate the absolute worst kinds of fats - trans fats."

"Anything that says 'partially hydrogenated' on the box ... should be viewed as having a skull and crossbones," he said. "Seriously - it's that bad for you."

Miller recommends that dieters lean more toward unsaturated and polyunsaturated fats. Those are found in olive oil and avocados; in fatty fish such as wild salmon, sardines and albacore tuna; in nuts such as almonds, walnuts and pistachios; and in dark chocolate.

Even good fats should be consumed in moderation because they're also rich in calories, Miller said: "The total fat content [of one's diet] could be 30 or 35 percent of your calories."

"The best way to cook ... is to steam your products," he said. Microwaving, grilling or sauteing are also OK.

Animal products are another source of saturated fats. "Choose lean cuts and no more than 3 or 4 ounces per serving," Miller said. "Instead of doubling your meat, double the green vegetables. Anything that's colorful is good for you - except Froot Loops."

Some commercial diet promoters said the new studies only confirm what they've argued for years - that lowering fats without making other dietary and lifestyle changes won't prevent heart disease and other ills.

"When you actually look at what kind of diet these women were on, it wasn't a good low-fat diet," said Marika Olsen, a spokeswoman for the Pritikin Longevity Center, in Florida.

The Pritikin diet gets less than 20 percent of its calories from fats, and those should be "heart-healthy," Olsen said. Pritikin also promotes complex carbohydrates, "modest" amounts of lean protein and reduced salt.

The women in the study, most of whom were overweight, might have stayed healthier had the protocol also forced them to lose weight and get more exercise, said Dr. Roger S. Blumenthal, director of the Johns Hopkins Ciccarone Preventive Cardiology Center.

"We don't want people to get the wrong message, that diet doesn't mean anything," he said. "But diet without weight loss probably is very unlikely to have a significant health benefit. Combine diet with better exercise habits."

Bonnie Liebman, director of nutrition at the Center for Science in the Public Interest in Washington, said she worries that consumers will be misled by the study:

"What I fear is that people will hear 'All fats are OK.' This message could really do harm. It could undo a lot of the progress we've made over the years."

Despite their impatience, some consumers were staying the course yesterday.

Betsy Boyd, at Atwater's in Belvedere Square, was enjoying a vegetarian soup for lunch. "I've always thought it smart to do everything in moderation and have a great time," she said.

Nearby, 74-year-old Joseph Napora and fellow jogging enthusiast Tim Satterfield, 45, were having sweet potato bisque with very little cream. They were dipping dark, grainy bread into olive oil - the good kind of fat.

"There's a lot of common sense involved in all this," said Satterfield, a business consultant from Monkton who is training for the Boston Marathon. "I think a lot of exercise is important, too."

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