Decades after Americans have switched from whole milk to skim, from butter to olive oil, and from red meat to turkey breast — all in an effort to cut saturated fat — nutrition researchers have concluded that saturated fat might not be so bad for our hearts after all. A new study getting a lot of attention this week analyzed a giant trove of data from 27 clinical trials and 49 population studies and found no difference in heart disease rates among those who had the least amount of saturated fat compared to those who ate the most.

People given fish oil supplements in clinical trials were no less likely to have a heart attack or die of heart disease than those who took placebos. Ditto for those who switched to olive oil — a monounsaturated fat shown to improve cholesterol levels — as well as for those who embraced polyunsaturated fats, like vegetable oil.

The new study, published in the Annals of Internal Medicine, found that only trans fats from partially hydrogenated oils were linked to a moderately higher rate of heart disease, but these artificial fats have largely been taken out of the food supply and will likely be banned altogether by the US Food and Drug Administration.

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“I think the evidence is really clear that the dietary guidelines shouldn’t be focusing on reducing saturated fat,” said study coauthor Dr. Dariush Mozaffarian, an epidemiologist at Harvard School of Public Health. “There is no good evidence that low-fat dairy products are healthier than high-fat dairy.” His previous research found that those who ate butter, whole milk, and cheddar cheese had a lower diabetes risk than those who opted for skim milk and fat-free yogurt.

Guidelines issued by the American Heart Association and American College of Cardiology last November recommended limiting saturated fat intake to no more than 5 to 6 percent of the total calories consumed to prevent heart disease. The average American currently eats about 11 percent of calories from saturated fat, less than the average consumed a few decades ago.

Those recommendations were based on “very strong, very clear” studies showing that lowering saturated fat intake lowers the level of LDL cholesterol, the type considered to be heart-damaging, said Tufts University nutrition professor Alice Lichtenstein, a coauthor of the new guideline. “To give people the message that they don’t have to worry about saturated fat and can go back to butter, cheese, and lots of red meat would be really wrong,” she added.

Where the nutrition experts do agree: Getting a clear picture on how the body handles dietary fats is very complex. For example, studies haven’t demonstrated that the LDL-raising effects of consuming saturated fats leads to more heart attacks and strokes. “Saturated fat in the diet makes LDL particles bigger, but it doesn’t increase the number of LDL particles, which we now think is responsible for the increased heart risk,” Mozaffarian said.

Complicating matters further, the body manufactures its own artery-clogging fats in the liver, often from excess carbohydrates that we eat.

“This is very confusing for everyone,” said Marion Nestle, a nutrition professor at New York University,“ and I think the scientific debate will continue for a while, so what are we supposed to do until then?”

Nestle’s advice echoes what our grandmothers told us: eat all things in moderation. “We should be enjoying the pleasure of food, but in very small portions.” Eating a quarter-pound burger once or twice a month is a far cry from eating the 22-ounce ribeye at Morton’s once or twice a week.

Where we also get into trouble is when we overdo on the oils by frying our foods in them. Another intriguing new finding from the Harvard School of Public Health found that people with a genetic predisposition for obesity—based on certain gene mutations that they inherited—were twice as likely to become obese if they reported eating fried foods more than four times a week compared to those with the genetic predisposition who ate fried foods less than once a week.

“We should be encouraging everyone to reduce the consumption of fried foods,” said study leader Lu Qi, since such a move could help mitigate any genetic tendencies toward obesity.

Was it worse to fry in butter than olive oil? “We didn’t look at that,” Qi said. “We found that all fried foods were bad.”