The Problem With PUFA

In my last post, The Common Enemy in Nutrition, I discussed how different nutritional camps that can’t seem to agree on much, agree that the average diet is too high in polyunsaturated fats and we’d have better health outcomes if we reduced those levels. In this post, I am going to list the problems associated with high PUFA consumption.

I am not a health professional, so I will be linking to all my sources. If I get something wrong, please leave a comment.


The article Polyunsaturated Oils Increase Cancer Risk by Dr. Barry Groves goes into not only the history of vegetable oils but how they suppress the immune system and are likely to promote cancer growth.

“Many laboratories have shown that diets high in polyunsaturated fatty acids promote tumours. Cancer promotion is not the same as cancer causing. The subject is complex; suffice to say here that promoters are substances that help to speed up reproduction of existing cancer cells.”

“’Vegetable oils (eg Corn oil and sunflower oil) which are rich in linoleic acid are potent promoters of tumour growth.”

The Big List

Health researcher Chris Kresser assembled a list of diseases connected to elevated n-6 levels. From the post How too much omega-6 and not enough omega-3 is making us sick:

…elevated n-6 intakes are associated with an increase in all inflammatory diseases – which is to say virtually all diseases. The list includes (but isn’t limited to):

  • cardiovascular disease
  • type 2 diabetes
  • obesity
  • metabolic syndrome
  • irritable bowel syndrome & inflammatory bowel disease
  • macular degeneration
  • rheumatoid arthritis
  • asthma
  • cancer
  • psychiatric disorders
  • autoimmune diseases

Low Metabolism and Thyroid Issues

You can’t have an article about excess PUFA without mentioning Dr. Ray Peat. From his article Unsaturated fatty acids: Nutritionally essential, or toxic?:

“A series of studies about 20 years ago showed that the functions of the thyroid hormone are all inhibited by unsaturated fats, with the inhibition increasing in proportion to the number of unsaturations (double bonds) in the fat molecule.”


“When the tissues are saturated with those antithyroid fats, metabolism slows, especially when any stress, such as cold or hunger, increases the concentration of free fatty acids in the blood stream. “

But how? For that part of the puzzle, I found this explanation in a post by Tom Brimeyer, who has a site that focuses on thyroid health.

  1. Polyunsaturated fats block the thyroid gland from secreting thyroid hormone.
  2. Polyunsaturated fats block the transport of thyroid hormone to your cells within your bloodstream.
  3. Polyunsaturated fats block your cells from properly utilizing the thyroid hormone that is available.

Peat’s article also goes into how PUFA increases estrogen levels which can lower body temperature. The site Functional Performance Systems has a page on that very topic.

Corn Oil Margarine

Photo by 1950sUnlimited. Full image on Flickr. 

Animal Obesity…What About Humans?

I found another Ray Peat article to be very interesting. Suitable Fats, Unsuitable Fats: Issues in Nutrition explains the history of what fats were used to fatten animals.

“The highly unsaturated seed oils had the opposite effect, of producing a rapid fattening of the animal, while decreasing feed consumption, so by 1950 corn and soybeans were widely considered to be optimal feeds for maximizing profits in the production of meat animals. It was at this time that the industry found that it could market the liquid oils directly to consumers, as health-promoting foods, without bothering to turn them into solid shortening or margarine. Somehow, few physiologists continued to think about the implications of metabolic slowing, obesity, and the related degenerative diseases.”

I bring this up as a possible problem with PUFA that might extend to humans. If the seed oils fattened farm animals on less feed then that demonstrates a metabolic lowering effect that could affect other mammals, including humans.  Again, I am not an expert, but this information combined with the previous section on thyroid and metabolism could explain a connection between high PUFA intake and obesity.

Beth at Weight Maven has a post titled Our Western diet: Prescription for Disaster? that connects how foods high in Linoleic Acid (LA) such as vegetable oils when combined with high insulin foods could increase appetite and lead to overeating.


From the same Ray Peat article as above.

“Unsaturated fats are more water soluble than saturated fats, and they are involved in many problems of permeability and edema.”

WebMD defines edema as “whenever small blood vessels become “leaky” and release fluid into nearby tissues”.


This one appears to have some disagreement. Ray Peat believes PUFA is 23 times more glycating than simple sugar. Dr. Chris Masterjohn disagrees.  For more information on glycation read Aging and Longevity – 3. Glycation.

Excess PUFA is Bad News

There are a lot of bad things that can happen to your body when your o-6 levels get too high. So far I’ve just used the terms “excess” and “too high” when describing PUFA levels. In the next post, I am going to quantify both the levels in food as well as what many leading experts recommend.

Part 3: Quantifying PUFA, Expert Opinion, and My Conclusion


Add yours

  1. Beth@WeightMaven

    Nov 28, 2013 — 5:14 am

    Have you seen Bill Lands NIH presentation? Well worth a watch re amount of PUFAs. Here’s part 1:

  2. @Bath – Thanks for sharing. I just finished watching all 4 parts. He mentioned that Americans were at 80% O-6. Is there a test one can do to measure their own levels?

  3. I think it was on Ben Greenfield’s website that I read that a high intake of OM-6 from nuts (or almonds specifically I’m not sure) wasn’t associated with health problems (I don’t have the link sorry). We should probably distinguish OM-6 from natural food sources vs OM-6 from processed seed oils invented in the 20th century.

  4. @Michael – I’m not certain about that, especially after watching the 4 part videos Beth linked to. Seems to me this is a math problem, but I will agree that one eliminate the seed oils first.

  5. Beth@WeightMaven

    Nov 29, 2013 — 9:24 am

    I’ve seen omega ratio tests advertised, but they test blood levels of o3/o6, not what’s stored in adipose. I’m not sure how helpful that is if your diet is dialed in.

  6. “Is there a test one can do to measure their own levels?”

    there’s one called HS-Omega-3 Index:

    “The HS-Omega-3 Index uses a standardized methodology to measure the percentage of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) in red blood cells. It also measures the ratio of omega 3 to omega 6.”

    the Life Extension Foundation offers a similar test (Omega Score) but I don’t know if it’s based on the same protocols as HS-Omega-3. The cost of these tests seems to be between 120-180$

  7. @Michael – Thanks. I found the follow up post where that blog posted their results.

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