People who lay off butter and cheese and pour olive oil onto their salads instead live longer and lower their risk of heart disease, researchers reported Monday.

It’s one of the longest and most detailed studies yet about what, precisely, to substitute for artery-clogging fats and the answers are clear: although most Americans substitute sugary treats and white bread, the better path is to go for vegetable oils and whole grains.

While the advice is nothing new, this study done by the Harvard School of Public Health puts numbers on it.

It doesn’t take much to cut the damage done by unhealthy fats.

Swapping just 5 percent of the calories from saturated fat found in dairy, lard or red meat to an equivalent amount of food rich in polyunsaturated fats such as soybean oil, sunflower oil, walnuts or fish lowers the risk of heart disease by 25 percent, Frank Hu and colleagues found.

, they wrote in their report, published in the Journal of the American College of Cardiology. Eating whole grain foods instead lowered the risk by 9 percent.

The findings fit in with another study that showed when people were given extra olive oil to add to their diets, they reduced their risk of heart disease.

But people who ate refined carbohydrates instead of the saturated fat — think white bread, sugar or white potatoes — didn’t lower their risk of heart disease at all. “In terms of heart disease risk, saturated fat and refined carbohydrates appear to be similarly unhealthful,” Hu said in a statement.

“Our findings suggest that polyunsaturated fatty acids, such as those from vegetable oils, nuts, and seeds, should have an expanded role as a replacement for saturated fatty acids,” Hu’s team wrote.

“However, our data and data from national surveys suggest that, when decreasing saturated fatty acid intake, most people appear to increase the intake of low-quality carbohydrates, such as refined starches and/or added sugars, rather than increase the intake of unsaturated fats.”

This may help explain why some early studies didn’t indicate that reducing saturated fats would lower heart disease risk, the researchers said.

For their study, Hu’s team used two big, ongoing studies of nearly 85,000 nurses and 43,000 doctors who fill out detailed questionnaires about what they eat every four years. They’ve been going for decades now.

They calculated what percentage of calories the volunteers got from each type of fat, from whole grains or from processed carbohydrates such as white flour and sugar.

In a second study in the same journal, Hu’s team tried to put similar numbers to intake of sugary drinks.

They reviewed the body of research on sugar-sweetened beverages such as soda and found that people who drink one or two servings a day of these drinks can raise the risk of type-2 diabetes by 26 percent, raise the risk of heart disease by 35 percent, and boost the risk of stroke by 16 percent.

“Part of the problem is how fructose behaves in the body,” said Hu. Glucose is quickly used as fuel while fructose, the main ingredient in high-fructose corn syrup, is metabolized in the liver and can be converted into triglycerides — one of the components of unhealthy cholesterol levels.

“Our findings underscore the urgent need for public health strategies that reduce the consumption of these drinks.”

But, they noted, half the U.S. population consumes fructose-sweetened drinks every day.

“Regular consumption of sugar-sweetened beverages can lead to weight gain because the liquid calories are not filling, and so people don’t reduce their food intake at subsequent meals.”

They recommend dropping the soda and changing snack habits — substituting nuts for potato chips and making sandwiches with whole-wheat bread and avocado instead of white bread and cheese.

“Our findings suggest that when patients are making lifestyle changes to their diets, cardiologists should encourage the consumption of unsaturated fats like vegetable oils, nuts, and seeds, as well as healthy carbohydrates such as whole grains,” Hu said.