Ray Peat on PUFA and Seed Oils

Short answer: Ray Peat considered polyunsaturated fats the main dietary cause of metabolic damage. He wrote that seed oils and fish oils suppress the thyroid and the immune system, promote inflammation and aging, and that the so-called essential fatty acids are not essential.

What Ray Peat wrote about polyunsaturated fats

He listed what they do: suppress metabolism and promote obesity, suppress immunity, cause inflammation, speed up the formation of age pigment, and promote free radical damage and cancer. Source: Membranes, plasma membranes, and surfaces, Fats and degeneration

He described the marketing in phases. First linoleic acid was sold as heart protective while saturated fat was blamed. Then omega-3 oils were said to be even better. Source: Fats and degeneration

He included fish oil. Fish oils are highly unsaturated and break down easily at body temperature. He points to studies in which fish oil or cod liver oil increased cancer, and to large studies that found no benefit for depression. Source: The Great Fish Oil Experiment, Fats and degeneration, Unsaturated Vegetable Oils: Toxic

He wrote that the unsaturated oils suppress the thyroid, and that they act as a misleading signal that pushes cells toward the diabetic state. Source: Diabetes, scleroderma, oils and hormones

With age, the most unstable fatty acids build up in tissues, and lipid peroxidation rises with them. Source: Unsaturated fatty acids: Nutritionally essential, or toxic?

Lard counts as a seed oil in practice, he said, because pigs are fattened on corn and soy. Source: Unsaturated Vegetable Oils: Toxic

Leaving them takes patience. It takes years to clear stored unsaturated fat from the tissues after the diet changes. Source: Preventing and treating cancer with progesterone

What he said to avoid and what to use

• Avoid corn, soy, safflower, flax, cottonseed, canola, peanut and sesame oil.
• Avoid cod liver oil. Lean fish and shellfish once or twice a week are fine.
• Coconut oil and olive oil are the only vegetable oils he called really safe. Butter and lamb fat are generally very safe.
• About 100 units of vitamin E a day covers an occasional restaurant meal.
• Aspirin and niacinamide help while the stored fat is being cleared.

Where he wrote about it

This topic comes up in 72 of the articles on his site. These are the most relevant ones:

• Suitable Fats, Unsuitable Fats: Issues in Nutrition · original on raypeat.com ↗
• Fats and degeneration · original on raypeat.com ↗
• The Great Fish Oil Experiment · original on raypeat.com ↗
• Glycemia, starch, and sugar in context · original on raypeat.com ↗
• Fats, functions & malfunctions · original on raypeat.com ↗
• Oils in Context · original on raypeat.com ↗
• Unsaturated fatty acids: Nutritionally essential, or toxic? · original on raypeat.com ↗
• Unsaturated Vegetable Oils: Toxic · original on raypeat.com ↗

My take

No omega-3, no omega-6 and minimal omega-9. The more double bonds a fat has, the less stable it is, and when it is built into cell membranes it weakens them. Coconut oil and butter are my fats.

Quick answers

What did Ray Peat say about seed oils?

That they are toxic to the energy-producing system of the cell, suppress the thyroid and the immune system, and promote inflammation, obesity, diabetes and cancer.

What did Ray Peat say about fish oil and omega-3?

He wrote that fish oils are highly unsaturated and oxidize easily in the body, that studies show they can increase cancer, and that the claimed benefits were marketing.

Which fats did Ray Peat consider safe?

Coconut oil, olive oil, butter and lamb fat.