Beef tallow, seed oils, and full-fat dairy: Are any of them heart-healthy?
A state-of-the-art review examined the pros and cons of these controversial fat sources.
- Reviewed by Walter C. Willett, MD, DrPH, Contributor
No wonder people are confused about healthy versus unhealthy fats. The latest federal dietary guidelines refer to beef tallow and butter as healthy. (Beef tallow is rendered fat from a cow.) But nutrition and heart experts alike have long encouraged people to steer clear of those animal-based fats, which are high in artery-clogging saturated fat.
Replacing animal fats with plant-based oils — including seed oils, which contain mostly unsaturated fat — is linked to a lower risk of heart disease (see “The upside of unsaturated fats”). Also known as cooking or vegetable oils, seed oils are extracted from the seeds of plants. Examples include canola, corn, safflower, sunflower, and soybean oils. But many social media influencers vilify seed oils, and U.S. Secretary of Health and Human Services Robert F. Kennedy even referred to them as poisonous.
A state-of-the-art review in the March 1, 2026, issue of JACC: Advances delves into the scientific evidence about the harms and benefits of these common fats, as well as of full-fat dairy. We asked Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, to weigh in on a few key questions.
The upside of unsaturated fatsWhen you eat unsaturated fats, the cells on the surface of your liver make more receptors that grab harmful LDL cholesterol from your bloodstream. Inside your liver, LDL particles are then broken down and removed from your body. In contrast, eating saturated fat tends to reduce the number of LDL receptors on liver cells and also makes those receptors less efficient. More LDL stays in your bloodstream, where it can accumulate inside your heart’s arteries, leaving you vulnerable to a heart attack. That’s an important part of the reason why replacing foods rich in saturated fat with foods high in unsaturated fat helps lower LDL and, in turn, decreases your risk of heart disease. |
Q: How does beef tallow compare to seed oils?
A: I agree with the review’s conclusion that beef tallow (which has more than 50% saturated fat) has adverse effects, while seed oils (which contain more than 80% unsaturated fat) have beneficial effects. Several randomized clinical trials have documented rises in harmful LDL cholesterol after people consume beef tallow. Research also points to other damaging effects, including worsening insulin control, fat accumulation in the liver, and blood vessel dysfunction.
In contrast, overwhelming evidence shows that consuming seed oils improves cholesterol levels, with dozens of randomized trials on canola oil alone. And contrary to popular belief, canola and other seed oils do not increase inflammation.
Q: Is full-fat dairy bad for heart health?
A: This answer is a bit more complicated. It depends on what outcome is being considered and whether we’re talking about butter versus other foods high in dairy fat, like cheese and yogurt. And another key issue is the comparison — what are you eating instead of dairy fat? If we compare butter with plant-based oils, butter is worse, both in terms of raising LDL cholesterol and heart disease risk. But if you swap out dairy fat for the same number of calories from refined grains (such as white bread, muffins, or cookies, for example), it’s not clear which is better. Nuts or peanut butter would be a healthier substitution for cheese, whereas processed meat would be worse.
The new dietary guidelines suggest three servings of dairy per day. But if all of them were full-fat versions, those foods alone would provide 8% of your calories as saturated fat (close to the recommended limit of less than 10%). I’d recommended limiting yourself to about one serving of full-fat yogurt or cheese per day, or maybe two if you don’t eat meat, which is another major source of saturated fat in the typical American diet.
Q: What about olive oil?
A: Olive oil isn’t highlighted in the review, perhaps because it’s not controversial. Extensive research dating back to the 1950s points to the health benefits of olive oil consumption, including improvements in heart-related risks such as cholesterol, blood pressure, and diabetes. As my colleagues and I found, replacing butter with olive oil or other liquid plant oils is associated with a lower risk of dying from heart disease, consistent with the effects on cholesterol levels seen in randomized trials.
Q: How to choose heart-healthy fats
A: In general, try to include more plant sources of protein such as nuts, soy foods, and other legumes in your diet over red meat and dairy foods. Doing so will naturally boost your intake of unsaturated fats while cutting your saturated fat.
For added fat, opt for liquid plant oils wherever possible. In my household, we use olive oil for almost everything — on bread, in salad dressing, and for cooking. But canola or soybean oil is a good choice when you want a more neutral flavor. We also occasionally use sesame oil, mustard oil, and coconut oil for their unique flavors.
For packaged foods, check the ingredients list and choose products that use unsaturated plant-based oils, such as canola or soybean. They’re healthier than palm or palm kernel oil, which are highly saturated fats that are popular thanks to their shelf-stable properties. Check the Nutrition Facts panel and look for products with a saturated fat content that’s less than one-third of the total fat content.
Image: © Deepak Sethi/Getty Images
About the Author
Julie Corliss, Executive Editor, Harvard Heart Letter
About the Reviewer
Walter C. Willett, MD, DrPH, Contributor
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