Cate Shanahan, M.D., whose May 22, 2020 appearance on “Real Time with Bill Maher” helped put her in the national spotlight, spent her professional life studying what constitutes the best diet for human beings. Her conclusions fill two books “Deep Nutrition” and her newest, “The Fatburn Fix.” Along with encouraging us to eat the nutrient-rich foods such as wild-caught fish with which we co-evolved, Dr. Shanahan wants to persuade us not to consume evolutionarily inappropriate foods. As she told Maher, one of the worst in her view is seed oil. What is seed oil, and why should we avoid it? Brad Lemley spoke with her about that and more.

Let’s talk about human beings and dietary fat. For most of human history, what kind of fat did we eat?

Certainly, it was whole-food-based fat, and most of it was of animal origin. Even when we began planting grains thousands of years ago, it was often to feed our animals – we noticed, for example, that wheat quickly made our animals get big faster.

When it comes to hunting for animals, some “paleo diet” researchers contend that all of the animals our ancestors hunted were very lean, so we should eat only lean meat. But most traditional hunters did much of their hunting in fall, when the animals had up to 30 percent bodyfat to prepare for winter. Traditional societies rendered that fat and kept it to eat later. Because it is composed of mostly saturated and monounsaturated fatty acids, it was chemically stable and did not go bad even without refrigeration.

Fatty fish were also clearly a huge part of ancestral diets. If you look at human migration patterns, nearly all are along coasts, because that’s where the food was abundant.

When did the fats we eat begin to change?

We first began to get extracted plant-fats from cottonseed. Plantations would have tons of it sitting around, so it was essentially free. The owners tried feeding the seed itself to animals, but the animals died. Eventually, scientists figured out how to use heat, pressure and solvents such as hexane to extract oil from it. This is not easy to do, as the oil is very “tightly invested” in the tissue of the seed.

Randy Hartnell and Dr. Shanahan

Vital Choice Founder and CEO Randy Hartnell with Cate Shanahan, M.D.

Nonetheless, these oils are very cheap to produce, much cheaper than the fats from animals such as tallow, lard or butter. So now we’ve transformed the world to make seed oils in abundance. When you fly over the Midwest you don’t see little mixed-crop farms. You see these giant circles of monoculture soy, corn, much of it used to make these oils.

What are “The Hateful Eight,” and what’s the problem with them?

My husband [and co-author] Luke asked me “How many of these seed oils are there? I said “eight” and he immediately came up with “The Hateful Eight” based on the [2015 Quentin Tarantino] film. We created an “Unwanted” poster featuring them.

Dr. Shanahan's "Hateful Eight" vegetable oils

Dr. Shanahan points out that of these, soy is the most commonly consumed – it fills deep fat fryers and is sold in stores, nearly always under the misleading term “vegetable oil.” Reprinted with permission.

These are toxic in multiple ways.

This oil is highly polyunsaturated, which means it is extremely chemically unstable. When heated, it quickly forms polymers [large molecular structures made of repeating rings or chains]. This tendency to polymerize makes these oils great as varnishes. Varnish is good for coating your furniture, not for nourishing your arteries, mitochondria or brain. In the body, these polymers either become toxic inflammatory agents or the body simply excretes them because they are not a food that our metabolism recognizes.

Because these polymers are considered pathogenic by the body, it ramps up inflammation to combat them. I honestly believe this is why so many children have food intolerances today – they are in a chronic inflammatory state from these oils that are so common in the food supply, and further inflammation from sugars and refined flours manifests as strong intolerance reactions.

Because they are so unstable and quick to polymerize, by the time the oil is extracted to put into a bottle, there is already enough degradation that up to five percent by volume is made of these dangerous polymers. Heating them for cooking creates even more. I consider modern seed oil a complex “soup” of toxins, all inappropriate for human health in different ways.

You recently went on “Real Time with Bill Mahar” to discuss your theory regarding seed oils and COVID-19 outcomes.

Yes, I believe strongly that in people under 65, virtually all of the truly serious complications we see from COVID-19 are an expression of an underlying highly inflammatory state that’s largely driven by these oils. I would be very surprised to find a single case of a person who made a concerted effort to avoid these oils who wound up very ill with this disease, unless they had a chronic serious infection or an immune disorder. The disease seems to be generally quite mild in people who have good metabolic health. This virus itself is not terribly aggressive, it simply reveals underlying metabolic inflammation. I am willing to stake my reputation on this. [One of the first, admittedly preliminary studies to examine unsaturated
oils and COVID-19 outcomes aligns with Dr. Shanahan’s view (El-Kurdi B et al. 2020)]

So, given this information, what kinds of dietary fats should we eat?

I just do the good fats: mostly butter, and olive oil for cooking. Olive oil is a fruit oil, not a seed oil – it gives up its fat easily with simple pressing, and is mostly monounsaturated, not polyunsaturated. Fat from cattle, pigs and fish is also part of a healthy diet.

For more, see Dr. Shanahan’s website,


El-Kurdi B, Khatua B, Rood C, et al. Mortality From Covid-19 Increases With Unsaturated Fat, And May Be Reduced By Early Calcium And Albumin Supplementation. Gastroenterology. 2020. doi:10.1053/j.gastro.2020.05.057.