Here’s what nutrition experts say about dietary fat

American dietary guidelines have gotten an overhaul. In January, the U.S. federal government unveiled a new food pyramid. Unlike the classic food pyramid, the new one is an upside-down triangle. Meat, full-fat dairy and olive oil appear near its top — suggesting people should eat a lot of those things. Grains and fruits are near the bottom, suggesting people should eat little of those.

Like the pyramid itself, the new emphasis on eating “healthy fats” seems to flip past nutrition advice. Previous guidelines favored fats from plants over those from animals. Now the guidelines list butter, beef tallow and olive oil as healthy fats.

Not so fast, say nutrition experts.

Most are on board with olive oil. It neither raises nor lowers a person’s risk of heart disease, says Marion Nestle. She is an expert in nutrition, food studies and public health at New York University in New York City. 

Telling people to use butter and other animal fats in place of plant-based ones is another story. That goes against years of health research, says Deirdre Tobias. She studies how nutrition affects the risk of getting diseases. She works at Brigham and Women’s Hospital and Harvard Medical School in Boston, Mass. 

When certain plant-based fats are eaten instead of animal ones, “you get the biggest bang for your buck,” says Tobias. Such plant-based fats can be found in vegetable and seed oils. Research clearly shows they are better for lowering risk of heart disease and diabetes, Tobias says. They’re also better for lowering risk of death overall.

Tobias was on the 2025 Dietary Guidelines Advisory Committee. That group issued a scientific report in December 2024 that did not push eating meat and dairy. Usually, dietary guidelines are based on that team’s report. But not this time. Instead, the U.S. government used documents put together by a different group of people. Notably, some of those people had ties to the meat and dairy industries.

The resulting guidelines encourage eating animal-based fats. The potential health risks of that guidance “is what was most concerning,” Tobias says.

Plus, when people change how much they eat of one thing, they tend to swap it for something else, says Kevin Klatt. This dietitian and nutrition scientist works at the University of Toronto in Canada. He worries that people who follow the message to eat more meat and full-fat dairy will cut fiber intake. If so, they could miss out on other nutrients in fruits, veggies and grains.

So, how can you really get enough healthy fats in your diet? Here’s what science says.

What are fats?

Let’s dive into the chemistry. Fat molecules are known as fatty acids. They’re made up of long chains of carbon atoms with some hydrogen and oxygen atoms attached.

Fats come in several varieties. First, there are saturated fats. They are called saturated because every carbon in the chain has all of its potential chemical bonds filled, or saturated. These fats show up in lard, butter, coconut oil, palm oil and beef tallow. They are solid at room temperature.

Then there are unsaturated fats. Those have one or more double bonds between carbons in the chain. A double bond introduces a kink in the chain. That keeps the molecules from packing together in an orderly fashion. The result is that unsaturated fats are usually liquid oils at room temperature.

Within unsaturated fats, there are two main types. One is monounsaturated. The other is polyunsaturated.

Monounsaturated fats have one double bond in their carbon chain. Oleic (Oh-LAY-ik) acid found in olive oil is a good example. Polyunsaturated fats have two or more double bonds in their chains. One example is conjugated linoleic acid, a natural trans fat. Fish, nuts and seeds are good sources of polyunsaturated fats.

Why are fats important?

Fats play many roles. For one, they form membranes around cells and organelles. Without them, life may never have developed as we know it.

Fatty acids also are important messengers. The molecules’ shape, chain length and other properties are clues that help the body decipher chemical instructions. Such messages are important for the brain and immune system to work.

On top of all that, fats store energy and nutrients, such as vitamins. They also cushion internal organs. 

But our bodies don’t make all the fats we need.

“You require fat in the diet because you need two different fatty acids,” Nestle says. One is linoleic acid (Lin-oh-LAY-ik). The other is alpha-linolenic acid. Those two fatty acids come only from the diet. “You don’t need a lot of them,” Nestle says. But they are building blocks for other fats.

Linoleic acid is a polyunsaturated fat that’s a type of omega-6 fatty acid. Omega-6 means that first double bond occurs at the sixth carbon from the end of the molecule. Nuts, seeds, legumes, eggs and meat are sources of linoleic acid.

Alpha-linolenic acid is a polyunsaturated fat of the omega-3 type. Omega-3 means the first double bond comes at the third carbon from the end of the chain. Fish, seafood, seeds and leafy green vegetables contain this fatty acid.

No natural foods contain purely one type of fat, Nestle says. “Fats that come in food are mixtures of saturated, unsaturated and polyunsaturated fatty acids. They are all mixtures. The only thing that varies is the proportion.”

Meat, dairy, palm oil and coconut oil have more saturated fats. Vegetable and seed oils tend to have more polyunsaturated fats.

Are saturated fats healthy?

Not really. 

Eating more saturated fat has been linked with higher levels of low-density lipoprotein, or LDL, Klatt says. People with more LDL have higher risk of heart attacks and strokes. That’s why it is often called “bad cholesterol.” (Cholesterol is a waxy substance in the body. Your cells need it to function properly, but too much can raise the risk of some diseases.)

For that reason, past dietary guidelines have recommended eating unsaturated fats. For instance, using olive, canola or soybean oils rather than butter.

Klatt and colleagues did a review of studies that examined the effects of that advice. Those studies had measured what happened when people reduced saturated fats in their diet. Or when they replaced saturated fats with polyunsaturated fats. The results were interesting.

For people at low risk of heart disease or strokes, cutting saturated fats didn’t make a big difference. Over five years, there was about 1 fewer death per 1,000 people who ate little saturated fat compared with those who ate lots.

People at high risk for heart disease or strokes saw bigger effects. (People in that group had high cholesterol, high blood pressure, diabetes, a smoking habit or past heart attacks.) For them, cutting saturated fat intake was linked with 6 fewer deaths per 1,000 people. It was also associated with 12 fewer nonfatal heart attacks per 1,000 people.

High-risk people fared even better if they swapped saturated fats with polyunsaturated ones. In that case, there were about 21 fewer nonfatal heart attacks per 1,000 people.

The researchers shared these findings December 16, 2025, in the Annals of Internal Medicine.

But such data have to be taken with a grain of salt. The reason: scientists can never tell exactly what people are eating. “We don’t keep people trapped in a [room] for five years and tightly control their diet,” Klatt says. The people in these studies may have swapped their fat intake for sugar or other less healthy foods.

Still, the trends suggest that polyunsaturated, plant-based fats are healthier than saturated, animal-based ones.

How do calories fit into the picture?

Calories count, too.

Past dietary guidelines haven’t only advised limiting fat intake for specific health reasons. They’ve also used it as a way to cut down on the calories people consume.

“All fats, across the board, whether saturated, unsaturated or polyunsaturated, have 120 calories per tablespoon,” Nestle says. “The idea that you should go easy on fat comes from the fact that they have nine calories per gram.” That’s twice as many calories as in proteins or carbohydrates.

“If you eat a lot of fat,” Nestle says, “you’ve got to reduce your calories someplace else.”

The new guidelines advise limiting saturated fat to no more than 10 percent of daily calories. (Healthy diets for most people ages 14 and up have about 2,000 calories per day.) That matches past guidance. But the new advice to eat more meat and full-fat dairy makes it hard to stick to that limit, Klatt says. Eating low-fat dairy and plant-based foods would offer more ways to get enough nutrients without too many calories.

“When you skim a milk and take out the fat calories, you leave all the protein. You leave all the calcium. You’re keeping all the essential nutrients. But now you just have fewer calories,” Klatt says.

“Saturated fats are nonessential fats. You don’t need them to survive,” Klatt adds. Human bodies already make all the saturated fat people need. In the diet, “all they do is raise [disease risk] and add calories without really adding much else.”

Are seed oils healthy?

Compared to saturated fats, yes.

Seed oils such as soy, canola and flax are missing from new dietary guidelines, Klatt says. Past guidelines suggested using seed or vegetable oils in small amounts for cooking or in salad dressing and sauces. Seed oils tend to have a high ratio of polyunsaturated fats to saturated fats. And they are rich sources of the two essential fatty acids — linoleic acid and alpha-linolenic acid.

Polyunsaturated fats have been tied with better health outcomes compared with other types of fats. (This is especially true for omega-3 fatty acids, such as alpha-linolenic acid.) In the short term, swapping saturated fats with polyunsaturated fats has been linked with lower “bad cholesterol” levels. In the longer term, people with more polyunsaturated than saturated fats in their diets tend to have fewer heart health problems.

But seed oils have gotten a bad rap lately. Why? “Consumption of seed oils rose in parallel with the rise in prevalence of obesity between 1980 and 2000,” Nestle says. But seed oils aren’t necessarily to blame for higher obesity rates, she adds. “People started eating more of everything during that period, not just seed oil.”

People may have become suspicious of seed oils lately for other reasons, too.

Some seed oils have a higher ratio of omega-6 linoleic acid to omega-3 fatty acids. In the body, linoleic acid gets turned to arachidonic (Ah-rak-ih-DON-ik) acid. And that fatty acid helps promote inflammation. Inflammation plays a role in many chronic health problems. But it is also necessary for wound healing and fighting infections.

Plus, “simply eating more linoleic acid doesn’t lead your cell membranes to become more rich in arachidonic acid,” Klatt says. The body controls its production of arachidonic acid and the inflammation that results. So if someone eats more linoleic acid? Their body will just dial back how much arachidonic acid it makes.

Another reason people worry about omega-6 fatty acids is that they compete with omega-3s in the body. Omega-6s can snatch up enzymes that omega-3s could use to build important fats. One of those is a fat called DHA (docosahexaenoic acid). Another is EPA (eicosapentaenoic acid).

Klatt has a solution for that: Eat more fish. Fish are already rich in DHA and EPA. So “you don’t have to worry about your body making its own.”

Maybe one type of seed oil contains a better ratio of omega-3s to omega-6 fatty acids than another. But “it doesn’t make the other one unhealthy,” Tobias says. “They’re all healthier than butter and tallow.”

In short, nutrition experts’ advice hasn’t changed. You might stick with skim rather than full-fat milk. And keep using olive oil and fish as fatty acid sources. That can help you get all the fats your body needs — without raising your health risk.