Know the facts about fats - Harvard Health (2024)

You need adequate amounts of good dietary fat.

Image: © JulijaDmitrijeva/Getty Images

Low fat? No fat? Try more fat. Dietary fats are essential for maintaining good overall health, especially as you age. "Your body needs a regular intake of fat," says Vasanti Malik, a research scientist with the Department of Nutrition at Harvard's T.H. Chan School of Public Health. "Fat helps give your body energy, protects your organs, supports cell growth, keeps cholesterol and blood pressure under control, and helps your body absorb vital nutrients. When you focus too much on cutting out all fat, you can actually deprive your body of what it needs most."

Two types of fats

To understand the role fats play in a healthy diet, you have to look closer at the two types of dietary fats: saturated and unsaturated. (A third kind, trans fats, have been all but eliminated from U.S. foods.)

Saturated. This is the so-called "bad" fat. It's primarily found in animal products like beef, pork, and high-fat dairy foods, like butter, margarine, cream, and cheese. High amounts of saturated fat also are found in many fast, processed, and baked foods like pizza, desserts, hamburgers, and cookies and pastries. These fats tend to more "solid" (think butter or lard) than healthier fats.

Unsaturated. This is the healthy kind, and there are two types: monounsaturated and polyunsaturated. Monounsaturated fats are found in avocados and peanut butter; nuts like almonds, hazelnuts, cashews, and pecans; and seeds, such as pumpkin, sesame, and sunflower seeds. It is also in plant oils, such as olive, peanut, safflower, sesame, and canola oils.

Polyunsaturated fats include omega-3 fatty acids and omega-6 fatty acids. Polyunsaturated fats are found in plant-based oils like soybean, corn, and safflower oils, and they're abundant in walnuts, flaxseeds, sunflower seeds, and fish like salmon, mackerel, herring, tuna, and trout.

The main health issue with dietary fats is how they influence cholesterol levels. Consuming high amounts of saturated fat produces more LDL (bad) cholesterol, which can form plaque in the arteries and increase your risk of cardiovascular disease and stroke.

"Many processed and fast foods made with saturated fat also contain high amounts of calories, which can lead to weight gain and further raise your heart disease risk," says Malik.

In comparison, the unsaturated fats help to raise HDL (good) cholesterol levels. HDL picks up excess LDL in the blood and moves it to the liver, where it is broken down and discarded. "You want to have a high HDL-to-LDL ratio, and unsaturated fats can help with this," says Malik.

But research has found that it's not enough just to eat more healthy fats. You also have to cut out the unhealthy saturated fat, too. A study from Harvard researchers in the March 2018 issue of The American Journal of Clinical Nutrition found that consuming monounsaturated fats, especially from nuts and olive oil, can lower a person's risk of heart disease — especially if the healthy fat replaces saturated fat and refined carbs (which can also raise LDL levels). The researchers added that any benefit from consuming monounsaturated fats may be negated if a person continues to consume too much saturated fat.

Feeding the brain

Another benefit of eating more "good" fat and less "bad" fat is that this can keep the brain healthy, says Malik. Studies have found a strong association between people who follow the MIND diet and a lower risk of Alzheimer's disease. The MIND diet advocates eating more of 10 certain foods and less of five others. Among the good ones are healthy-fat foods like nuts, fatty fish, and olive oil, while the bad ones — butter, cheese, red meat, pastries, and fried and fast foods — contain high amounts of saturated fat.

A 2015 study in the journal Alzheimer's & Dementia looked at more than 900 people ages 58 to 98 who filled out food questionnaires and underwent repeated neurological testing. It found that those whose diets most closely followed the MIND recommendations had cognitive function equal to that of a person more than seven years younger.

The association between healthy fats and healthier brains may be related to inflammation. "Diets high in saturated fats appear to raise inflammation, while eating unsaturated fats can dampen the inflammatory response," says Malik.

Focus on quality

How much dietary fat should you eat each day? The most recent Dietary Guidelines for Americans have moved away from suggesting a specific amount of fat. However, they still emphasize keeping saturated fat intake to less than 10% of daily total calories.

Malik suggests it's easier to focus on quality and not quantity. "Add more foods with mono- and polyunsaturated fats to your diet, and stay clear of those with saturated fats," she says.

A simple strategy is to add some healthy fat to every meal. "Since both kinds of unsaturated fats are healthy, don't worry about getting equal amounts of each," says Malik.

For example, spread avocado on toast, make a nut butter sandwich for lunch, and add a handful of nuts as an afternoon snack. Buy an oil brush and apply olive oil to chicken breasts and vegetables.

"You don't have to make major changes to your eating habits to get the right fat into your diet," says Malik.