For decades, the message was loud and clear: high intake of fat causes weight gain, heart disease, and maybe even cancer. The solution? Go low-fat. Unfortunately, that often meant consuming more carbs and more sugar.
Today, that advice is considered misguided. Nutritionists now suggest people actually need adequate amounts of fat for optimal health -- but only the right kind.
"The evidence is clear that your body needs a regular intake of good fat," says Dr. Frank Hu, a professor of nutrition and epidemiology at Harvard's T.H. Chan School of Public Health. "Good fat gives your body energy and helps your body absorb vital nutrients."
The weighty facts about fat
Despite what you may think, fat itself does not cause you to gain weight; excess calories lead to weight gain. But many foods high in saturated fat also happen to be high in calories, says Dr. Frank Hu of Harvard's T.H. Chan School of Public Health. "This is why overindulging in high-calorie fast and processed food, which also happens to be high in saturated fat, refined starch, and sugar, can lead to excess weight."
There are two main kinds of fat: saturated and unsaturated.
Saturated fat is in animal products like beef, pork, and dairy products like butter, cream, and cheese. Saturated fat also is a staple in most fast, snack, and processed foods, such as pizza, dairy desserts, bacon, and cookies. If it's considered junk food, odds are it contains saturated fat.
Unsaturated fat comes in two categories: monounsaturated and polyunsaturated. Monounsaturated fats are found in avocados, peanuts, peanut butter, and nuts like almonds, hazelnuts, cashews, pistachios, and pecans. High amounts are also in oils, such as olive, peanut, safflower, sunflower, and canola oil.
Polyunsaturated fats include omega-6 fatty acids and omega-3 fatty acids. They also are considered "essential" fats because your body can't make them, and you have to get them from food. Omega-6s are in oils like soybean, corn, sesame, and canola. They're also abundant in walnuts, peanuts, and pumpkin seeds. Omega-3s are in canola oil, soybean oil, and walnuts, as well as in fatty fish, like salmon, mackerel, herring, tuna, and trout.
Friend and foe
How does fat help -- and hurt -- your health? Too much saturated fat can raise "bad" LDL cholesterol levels. High blood LDL can lead to plaque buildup in arteries throughout the body, which increases the risk of not only heart attacks and strokes, but also erectile dysfunction and poor leg circulation.
"Cut out saturated fat in your diet, and you can lower your risk for all these problems," says Dr. Hu.
In comparison, consuming monounsaturated and polyunsaturated fats helps lower blood pressure and reduce chronic inflammation, which translates to lower cardiovascular risk.
In fact, a report published in the April 2018 issue of the Annals of Nutrition & Metabolism said that replacing just 5% of saturated fat in one's diet with unsaturated fat was associated with a 17% lower risk of cardiovascular disease. Research also has found that choosing unsaturated fat over carbohydrates and saturated fat can help lower blood sugar levels and reduce the risk of diabetes (assuming a similar daily caloric intake).
Healthy fats, healthy brain
Another benefit of switching fats is that it might help keep your brain healthy. Studies have found a strong association between people who follow the MIND diet and a lower risk of Alzheimer's disease.
This research-based diet -- the name stands for Mediterranean-DASH Intervention for Neurodegenerative Delay -- advocates eating more of certain foods that are high in unsaturated fat, like nuts, fatty fish, and olive oil. The diet also stresses cutting down on foods that contain high amounts of saturated fat, such as butter, red meat, pastries, and fried and fast foods.
A small but growing body of evidence shows an association of these dietary changes with less depression, age-related memory loss, and cognitive decline. The connection could be related to unsaturated fat's ability to dampen chronic inflammation, according to some experts.
So how much unsaturated fat is enough? The Dietary Guidelines for Americans 2020-2025 say the total daily fat (saturated and unsaturated) for men age 60 and older should make up 20% to 35% of their daily calories -- or about 44 to 78 grams of total fat per day. "Of course, most of this should come from good unsaturated fat," says Dr. Hu. "You should keep saturated fat intake to no more than 10% of total calories."
Keeping track of percentages and grams, though, can be tricky. A better approach is to focus on quality rather than quantity, according to Dr. Hu.
For instance, other diets similar to the MIND diet, like the Mediterranean and DASH diets, also emphasize high amounts of unsaturated fat and limit saturated fat-rich foods. "Following these types of diets means you don't have to worry about not getting enough fat or the right kinds," says Dr. Hu.
Another option is to replace saturated fats with healthier fats in your daily diet. For example:
Spread avocado, peanut butter, or almond butter on toast instead of butter.
Instead of commercially bottled salad dressing, mix your own from equal parts olive oil and vinegar.
Use oils like olive, peanut, or corn for flavoring and as a substitute for butter whenever you bake or sauté.
Replace red meat with fish and poultry (without skin).