Fat has had a bad rep since the 1980s, but like many things in nutrition, it’s not black and white. The types of fats matter too when we’re talking about the benefits or drawbacks of adding this macronutrient to your diet—and, of course, there are no “good” or “bad” foods. Still, you’ve probably heard the term healthy fats thrown around, but what does that really mean?
“Dietary fat for so long was vilified,” Amy Goss, Ph.D., R.D, an assistant professor in nutrition sciences at the University of Alabama at Birmingham, tells SELF. One reason, she says, is that people tended to associate eating dietary fat with cardiovascular disease and, as a result, became fearful about including fat in their diet.
It’s only relatively recently that people have started to acknowledge that the macronutrient has some serious positives to offer. Fat began a comeback during the low-carb trend of the early aughts, and today, high-fat keto diets are continuing to gain in popularity. At the same time, though, many people are still wary about incorporating too much of it into their meals. In fact, a 2020 study published in Nutrients found that when researchers asked college students to choose what they believed to be the healthiest meal, 73% of them picked a meal prepared with no fat.
That just shows we still have a long way to go when it comes to clearing up the misconceptions around fat and what it does to your body. Here’s what you need to know.
First of all, our bodies need fat for optimal health.
While talking about a healthy diet can certainly be complex—there are a lot of factors that go into it—the truth is that fat isn’t inherently unhealthy, and you actually need some of it for your body and mind to run at their best. “Fat is a very necessary part of the human diet, and it has a lot of functions,” says Dr. Goss. Our livers produce some fats, but we also have to eat certain fats to function. Fats are essential for cell growth and turnover, and they aid brain growth and development, digestion and satiety, hormone production, and absorption of vitamins A, D, E, and K, Dr. Goss says.
People tend to lose sight of these benefits when they focus on the caloric density of fat, says Dr. Goss. It is true that fat contains more calories per gram than protein or carbohydrates—9 calories per gram compared to 4 grams for each of those other macronutrients—but that doesn’t mean you should avoid fat because of it. The key, though, especially if you are looking to eat for heart health, is to consume the right amount of fat for your needs (more on that below) and focus on the most helpful kinds. While there are no “good” or “bad” foods, some types of fat can be more helpful to eat and others to limit if you’re looking to eat to keep certain health conditions in check, or if you have risk factors for one.
That’s because not all types of fats affect your body the same way. Saturated fats, unsaturated fats, and trans fats all function differently within your body. Unsaturated fats, which include monounsaturated fats and polyunsaturated fats, are generally regarded as “healthy” fats, but even they are not all alike.
But remember, like many things in the nutrition world, the right amount of fat to eat is very individualized, and there’s no one-size-fits-all plan that you must follow 100% of the time. In fact, it’s important to note that while there are general guidelines on fat consumption, we need more research to understand exactly how we can calibrate the fat content of our diets for our individual nutritional needs.
“We sort of have a paucity of data,” Sun H. Kim, M.D., M.S., assistant professor of medicine in the division of endocrinology, gerontology, and metabolism at the Stanford University School of Medicine, tells SELF. “A lot of diet recommendations are just guidelines guided by the industry or the experts, but it’s really hard to do a great diet trial.”
To help cut through the confusion, we talked to experts about the different types of fats, what the research shows, and the best way to incorporate them into your diet.
What are monounsaturated fats, and how much do you need?
Monounsaturated fats get their name from the one (thus mono) double bond between carbon atoms in their molecular structures. These fats are generally liquid at room temperature, but become solid when chilled—think olive oil, canola oil, and peanut oil. Other sources include nuts, seeds, and avocados.
According to the American Heart Association (AHA), monounsaturated fats are beneficial in your diet because they help reduce levels of low-density lipoprotein, the kind of cholesterol that can accumulate in your arteries and cause buildup. (It’s different from HDL, or high-density lipoprotein, which can actually remove the accumulation out of your arteries.) They also provide a hit of vitamin E, which serves as an antioxidant in your body and may protect your cells from damage.
Monounsaturated fats have been linked to a reduced risk of coronary heart disease, and in a 2018 study published in the American Journal of Clinical Nutrition, people who replaced dietary saturated fat with monounsaturated fats or omega-6 polyunsaturated fats (more on them below) for 16 weeks improved markers of blood vessel health.
Our bodies can make monounsaturated fats and store them for fuel, so these fats aren’t considered essential in your diet, and there’s no recommended dietary allowance that spells out exactly how much to eat. Instead, consider monounsaturated fats part of a well-rounded fat portfolio. According to the U.S. Department of Agriculture’s Dietary Guidelines for Americans, adults should consume about 20% to 35% of daily calories from fats, but no more than 10% should come from saturated fats. The rest should come from a mix of monounsaturated fats and polyunsaturated fats.
While food makers are required to list saturated fats on nutrition labels, they only have to list mono- and polyunsaturated fats if they are making specific claims about these fats in their food. Since you won’t always find an entry on a nutrition facts panel that says monounsaturated fats, it might be helpful for you to scout them out yourself.
What are polyunsaturated fats, and how much do you need?
Polyunsaturated fats have more than one carbon-carbon bond, which explains the poly in their name, and include both omega-3 fatty acids and omega-6 fatty acids. Omega-3s make up cell membranes and play a role in a variety of your body’s systems, and some omega-3s are known for their anti-inflammatory properties. Omega-6 fatty acids aid cell signaling and immune system activity, but some research suggests that in excess, they could overactivate your immune system and increase inflammation, J. Bruce German, Ph.D., a professor and chemist in food science and technology and director of the Foods for Health Institute at the University of California, Davis, tells SELF.
Two polyunsaturated fats—linoleic acid (an omega-6) and alpha-linolenic acid (an omega-3)— are essential to our diets; we can’t produce them in our bodies. For linoleic acid, the adequate daily intake ranges between 12 and 17 grams per day based on your age and sex, according to the Dietary Guidelines. Good sources include walnuts and sunflower seeds. For alpha-linolenic acid, it’s 1.1 to 1.6 grams per day. You can find this type of fat in flax seeds or flax oil.
The omega-3 fats eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) are sometimes called conditionally essential because we can make them, but don’t always make enough. There’s no specific recommendation on how much EPA and DHA to consume, but the AHA recommends eating two servings of fish, especially fatty fish like salmon, per week to take in a beneficial amount.
The Dietary Guidelines emphasize eating more polyunsaturated fats and less saturated fats, and research suggests that this tactic could be somewhat beneficial for overall health. In a 2020 meta-analysis in the journal Clinical Nutrition, people who ate the most polyunsaturated fats were 11% less likely to die of any cause over the study period. (There was a similar, but not as strong, relationship for those who ate the most monounsaturated fats—they had a 6% reduction in risk.)
In general, because omega-6s can be inflammatory in excess, a helpful strategy is to focus on eating more omega-3s so you can maintain a better balance between the two of them, says Dr. German. It can be tricky, since omega-6s are more prevalent in our food sources, meaning it can be easier to eat too much of them. Omega-6s are less susceptible to oxidation than omega-3s; they don’t go rancid as quickly, so they’re often used in commercial products like salad dressings. (You may see them listed as ingredients like corn oil or soybean oil.) Looking for products with olive oil or canola oil instead—which are rich in monounsaturated fats and won’t raise your omega-6 bottom line—can help you better achieve that balance, Dr. German says.
Like with monounsaturated fats, you might not see polyunsaturated fats listed on a nutrition label, so understanding the food sources of each type listed above can be helpful to determine if you’re including them in your diet.
Saturated Fats and Trans Fats
What are saturated fats—and should you limit them?
Saturated fats have no carbon bonds; their carbon atoms are saturated with hydrogen molecules instead. Foods rich in these fats, such as butter and coconut oil, are often solid at room temperature.
Saturated fats are not essential—you can make them on your own—and the Dietary Guidelines recommend consuming 10% or fewer of your daily calories from them. Unlike the prior types of fat, saturated fat is easy to spot because it’s listed on food labels. You’ll find them in baked goods, fried foods, fatty meats like bacon, sausage, and red meat, dairy products, and solid fats such as coconut oil, palm oil, and palm kernel oil.
As we mentioned above, saturated fats are commonly regarded as unhealthy due to their potential to contribute to heart disease risk. They also may play a role in non-alcoholic fatty liver disease—a growing concern around the world. In fact, a 2020 review published in the European Journal of Clinical Nutrition concluded that replacing saturated fats with unsaturated fats may help to reduce fat in the liver.
“Saturated fat increases LDL cholesterol; unsaturated fat decreases it,” Penny M. Kris-Etherton, Ph.D., a distinguished professor of nutrition at Penn State University, tells SELF. Saturated fat is also linked to triggering inflammation, while unsaturated fat tends to tamp it down, she says.
However, some recent studies have suggested that the link between saturated fat and heart disease might not be as clear-cut as once thought, finding no association with saturated fat consumption and risk of early death, death by heart disease, heart disease in general, or type 2 diabetes. “I’m not as worried about saturated fat as probably I used to be just because of the more recent evidence to come out,” says Dr. Goss. It’s important to note, though, that the AHA still recommends limiting them—more strictly than the Dietary Guidelines, in fact. The AHA recommends no more than 5-6% of daily calories come from saturated fat.
Like many things in nutrition, it’s difficult to make blanket assumptions with certain types of food, because there are tons of different factors that combine to make someone more or less at risk of a certain disease—not just one particular nutrient. For instance, Dr. Goss says the overall context of your diet likely plays a role in the effects of saturated fats on your health. If you tend to eat a lot of less nutritious high-carb foods (say, ones that contain added sugars, not ones like whole grains, fruits, or vegetables) with your saturated fat, for example, your body may be more likely to store this fat in the liver, contributing to fatty liver disease, Dr. Goss says.
It’s also likely that there is more to tease out regarding the relationship between saturated fat and disease. One relatively new way of thinking? All sources of saturated fat may not affect your body in the same way. For instance, whole-fat dairy and unprocessed meats, for example, may not be linked with heart disease, and coconut oil might not raise LDL cholesterol as much as animal fats do. Until we have more conclusive research, though, it makes sense to stick with the recommendations from the Dietary Guidelines or the AHA.
And continue to look at the bigger picture: Experts agree that establishing a healthy overall dietary pattern is more important than focusing only on reducing saturated fats. Some of the foods we eat that are high in saturated fat, like pastries and candy, are also rich in simple sugars or other components that can negatively affect health when consumed in excess. Remember, though, overall pattern is key, so you don’t have to overstress about every bit of saturated fat you take in, even if you are trying to stick to the guidelines—it’s not about one meal or one day of eating.
What are trans fats, and should you limit them?
If there’s any fat that deserves its bad rep, it’s probably trans fat, named for trans bonds in its molecular structure. Trans fats occur naturally in small amounts in some foods, like meat and dairy, because animals like cows and goats can produce these fats in their guts. (Your gut doesn’t make them, however.) Trans fats also used to be industrially produced and prevalent in snack foods you’d find at the store, such as cakes, pies, and cookies made with shortening, microwave popcorn, and refrigerated dough, like canned biscuits, as SELF reported previously.
More than a century ago, food manufacturers began making artificial trans fats by hydrogenating polyunsaturated vegetable oils so they stayed solid at room temperature. That’s the partially hydrogenated oil that you may have heard about. This process helps extend the shelf life of foods and give them a smooth texture. However, it comes with some serious drawbacks.
“They do seem, in population studies, to do the worst possible thing you’d want—they raise LDL, and they lower HDL,” says Dr. German. According to the AHA, eating trans fats can raise your risk of heart attack, stroke, and type 2 diabetes.
The good news is that the FDA has phased out industrially produced trans fats over the past few years. After 2018, most manufacturers were no longer able to add trans fats to foods, though some received limited, petitioned approval to use them until June of 2019. (They also had until January 2021 for the foods to work their way through distribution.) Research suggests that the naturally occurring trans fat might not be as harmful as the industrially produced ones, although more studies are needed. For now, stick with the Dietary Guidelines, which recommend reducing all trans fat as much as possible without compromising the overall quality of your diet.
While the evidence is pretty solid on the need to limit these non-natural sources of trans fat, there’s still a lot we need to learn about the other types of fat. Until that research is done—and we desperately need more research in diverse populations on a variety of health outcomes, says Dr. German—it’s best to consider your fat intake as one single component of your diet, not the defining factor of it. Consider how everything you eat fits together, says Dr. Goss. “The overall context of your diet does matter, and dietary fat can fit into a lot of healthy dietary patterns,” she says.