What the new nutritional guidelines do wrong about fat

When new dietary guidelines for Americans were released in early January, I couldn’t help but notice the “healthy fats” at the top of the inverted food pyramid.

Like the food pyramid itself, the new guidelines shake up previous nutritional advicewhich favored vegetable fats over animal fats. Now, the U.S. Department of Agriculture and the Department of Health and Human Services cite butter, beef tallow and olive oil as examples of healthy fats.

Not so fast, say nutrition experts.

Most are on board with olive oil. It’s neutral when it comes to heart disease, says Marion Nestlé, professor emeritus of nutrition, food studies and public health at New York University.

But telling people to use saturated fats like butter and other animal fats instead of plant-based unsaturated fats, like those found in vegetable or seed oils? That flies in the face of years of health research, says Deirdre Tobias, a nutritional epidemiologist at Brigham and Women’s Hospital and Harvard Medical School in Boston.

Epidemiological studies and long-term clinical trials have conclusively shown that when polyunsaturated fats are consumed in place of saturated fats, “you get what you pay for in terms of reduced risk of heart disease, cardiovascular disease, diabetes.” [and] all-cause mortality,” says Tobias, who was part of the 2025 Dietary Guidelines advisory committee.

This committee published a scientific report in December 2024, the focus was not on meat and dairy. Usually, the guidelines are based on the report of the advisory committee. Not this time. Instead, the agencies provided brief “science-based” documents developed by another group of advisers, some with ties to the meat and dairy industries. The potential health consequences of adding unhealthy fats to the diet “is what was most concerning in this exchange,” says Tobias.

The focus on fat also ignores the fact that when people stop eating one thing, they replace it with another, says Kevin Klatt, a registered dietitian and nutrition scientist at the University of Toronto. He worries that people who follow the message of eating more protein and high-fat dairy products will reduce their fiber intake and miss out on other essential nutrients found in fruits, vegetables and whole grains.

I spoke with these experts to give you the lowdown on fat.

What are fats?

Let’s move on to chemistry. Fats, or more precisely fatty acids, are molecules composed of long carbon chains with hydrogens and oxygen attached.

There are several varieties. There are saturated fats. They are called saturated because each carbon in the chain has all of its potential chemical bonds filled or saturated. These fats, like lard, butter, coconut oil, palm oil, and beef tallow, are solid at room temperature.

Then there are unsaturated fats. These have one or more double bonds between the carbons of the chain. A double bond introduces a twist into the chain, which prevents the molecules from stacking in an orderly manner. Unsaturated fats are generally oils that are liquid at room temperature.

Among the unsaturated fats are monounsaturated fats. These have a double bond in the chain. Oleic acid found in olive oil is a good example. Polyunsaturated fats have at least two double bonds. Fish, nuts and seeds are good sources of these fatty acids, including omega-3 and omega-6 fatty acids.

What do fats do in the body?

This is where it becomes real for many of us. Fats have many functions. They form membranes around cells and organelles. Without fats, life could still be in the primordial stage.

Fatty acids are important messengers. The shape of the molecule, the length of the chain and other properties of fats are clues that help the body decipher the instructions. Such messages are important for brain and immune function.

And fats store energy and nutrients, including certain vitamins, and protect internal organs.

Why do we need fats in our diet?

Our bodies don’t produce all the fats we need.

“From a nutritional point of view, you need fat in your diet because you need two different fatty acids, linoleic acid and linolenic acid,” explains Nestlé. These two fatty acids come only from food. “You don’t need a lot of it,” but these fats are building blocks for other fats.

Nuts, seeds, legumes, eggs and meat are sources of linoleic acid, one of the omega-6 fatty acids. Omega-6 means that the first double bond is located at the sixth carbon from the end of the molecule.

Fish, seafood, seeds and leafy green vegetables are sources of alpha-linolenic acid, the essential member of omega-3 fatty acids. Omega-3 means that the first double bond comes to the third carbon from the end. Omega-3 and omega-6 fatty acids are polyunsaturated.

No natural fat is purely one type, says Nestlé. “Fats found in foods are mixtures of saturated, unsaturated and polyunsaturated fatty acids. They are all mixtures. The only thing that varies is the proportion.” Fats from meat and dairy products as well as palm and coconut oils contain more saturated fats, while vegetable and seed oils, especially flaxseed oil, tend to contain more polyunsaturated fats.

Family tree of fatty acids

Fats come in two main varieties: saturated fats and unsaturated fats.

Saturated fats (red, to indicate that these fats are not essential to the diet and are associated with a higher risk of cardiovascular disease), such as butter, lard, and palm oil, are solid at room temperature.

Unsaturated fats are liquid at room temperature. Among unsaturated fats, there are monounsaturated fats (yellow, indicated as not necessary in the diet and neutral for the risk of cardiovascular diseases) and polyunsaturated fats (green, necessary and associated with a lower risk of cardiovascular diseases). Examples of foods containing monounsaturated fats are olive oil and avocados. Fish, eggs, nuts and seeds are good sources of polyunsaturated fats.

Polyunsaturated fats contain many subsets, primarily omega-3 and omega-6 fatty acids. Omegas include the two fats – linoleic acid (an omega-6) and alpha-linolenic acid (an omega-3) – that people must get from their diet because the human body does not produce them. Walnuts and flaxseed or chia seed oil are rich in alpha-linolenic acid. Almonds and peanut oil, safflower and grapeseed oils are some sources of linoleic acid.

Are saturated fats healthy?

Not really.

Nutrition research has generally shown that eating more saturated fat is associated with higher levels of low-density lipoprotein, LDL, also known as “bad cholesterol”, Klatt said. This type of cholesterol has been linked to a higher risk of heart attack and stroke. Previous guidelines used such links to chronic diseases recommend monounsaturated fats, such as those in olive oil, or polyunsaturated fats, such as canola or soybean oil, as healthier alternatives to butter or other animal fats.

Klatt and colleagues reviewed studies investigating the effects of reducing saturated fat in the diet or replacing saturated fat with fat s polyunsaturated. The results were interesting.

For people at low risk of cardiovascular disease, cut saturated fats had a statistically insignificant effect, the researchers reported Dec. 16 in the Annals of internal medicine. Over five years, there was about 1 fewer deaths per 1,000 participants who ate little saturated fat than among those who ate a lot.

But for high-risk people — those with high cholesterol, high blood pressure, diabetes, smokers, or those who have already had a heart attack — lower consumption of saturated fat was associated with 6 fewer deaths and 12 fewer nonfatal heart attacks per 1,000 study participants, a statistically significant reduction. And those at high risk fare even better if they replace saturated fats with polyunsaturated fats. This exchange resulted in approximately 21 fewer non-fatal heart attacks per 1,000 participants.

But nutrition research is difficult because scientists can I never really say what people eat and whether they trade fat for sugar or other less healthy foods. “We don’t keep people locked in a metabolic ward for five years and tightly control their diet,” Klatt says. “You can’t put it in a pill and randomize people [to eat] fat or placebo.

How do calories fit into the chart?

Calories count.

Previous dietary recommendations advised limiting fat intake not only for specific health reasons, but also to reduce the number of calories consumed.

“All fats, whether saturated, unsaturated or polyunsaturated, contain 120 calories per tablespoon. The idea that you should go easy on fats comes from the fact that they contain nine calories per gram,” says Nestlé. This is twice as many calories as protein or carbohydrates. “If you eat a lot of fat, you need to cut your calories elsewhere.”

Current guidelines advise limiting saturated fat intake to no more than 10% of daily calories. This is consistent with previous recommendations. But new advice to eat more meat and whole-fat dairy products makes it difficult to stick to these recommendations. limit, says Klatt. This is a problem because previous guidelines that recommended fat-free or low-fat dairy and plant-based diets gave more leeway in getting nutrients while controlling calories.

For example, “when you skim a milk and remove the fat calories, you leave all the protein, you leave all the calcium. You keep all the essential nutrients, but now you just have fewer calories, which gives you a lot more to work with in a diet,” says Klatt.

“Saturated fats are nonessential fats. You don’t need them to survive,” he says. The human body already produces all the saturated fats it needs. In the diet, “they only raise [cardiovascular 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 conspicuously absent from dietary guidelines, says Klatt. Previous dietary guidelines suggested using seed or vegetable oils in small amounts for cooking or in salad dressings and sauces. Seed oils tend to have a high ratio of polyunsaturated fats to monounsaturated or saturated fats, and are rich sources of both essential fatty acids.

Polyunsaturated fats, particularly omega-3 fatty acids, have been linked to better health outcomes than other types of fats. In short-term studies, replacing saturated fats with polyunsaturated fats has been associated with lower levels of LDL (often called “bad cholesterol”). And longer-term studies have shown that people whose diets contain more polyunsaturated than saturated fats tend to have fewer heart health problems.

But seed oils have gotten a bad rap lately.

Guilt related to the association with fried or ultra-processed foods could be partly to blame, according to Nestlé. “Consumption of seed oils increased alongside the increase in obesity prevalence between 1980 and 2000. But this is an association, not necessarily causation, because people started eating more of everything during this period, not just seed oil.”

What about the chemistry of seed oils?

Chemistry may play a role in the recent vilification of seed oils, Klatt says.

Some seed oils have a higher ratio of omega-6 linoleic acid to omega-3 fatty acids. In the body, linoleic acid is converted to arachidonic acid, which helps promote inflammation. Inflammation plays a role in many chronic health conditions, but is also necessary for wound healing and fighting infections.

But there is no direct cause and effect in terms of food. “Simply eating more linoleic acid does not cause your cell membranes to become richer in arachidonic acid,” says Klatt. Indeed, the body regulates both the production of arachidonic acid and the inflammation it causes. So if a person consumes more linoleic acid, the body will simply reduce the production of arachidonic acid, he says.

Another reason people are concerned about omega-6 fatty acids is that they compete with omega-3s for enzymes that elongate fatty acids into other important fats. Some people worry that increased consumption of omega-6 fatty acids may interfere with the production of longer-lasting omega-3s, such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

Klatt has a solution for this: eat more fish. Fish is already rich in DHA and EPA, so you don’t have to worry about your body making its own from the plant precursors you get in soybean and canola oil.

Even if one type of seed oil contains a more favorable ratio of omega-3 to omega-6 fatty acids, Tobias says, “that doesn’t make the other unhealthy, because they’re all healthier than butter and tallow.”

After chewing the fats with nutrition experts, I decided to stick with skim milk.. And I will continue to use olive oil and fish as sources of fatty acids. This way I’m not increasing calories while trying to get the essential fats my body needs.