Case Study: 30-Days of High Omega-6 Diet--Stiffens Arteries and Increases Belly Fat

Bottom line: A daring journalist eats a high omega-6 diet for 30-days (think Super-Size Me), which results in stiffer arteries, lowered metabolism, and an increase in belly fat.

Background: Journalist and author, Susan Allport, sold Oprah magazine on the idea of a “super-size me ” version of eating a high omega-6 fat diet for 30 days.  Bravely, she offered to be the human guinea pig.  What makes Susan particularly valiant is that she was well aware of the health hazards of eating a high omega-6 diet, as it was the subject of her book, Queen of Fats.

Although Susan willingly subjected her body to a daily dietary omega-6 bombardment for 30-days and chronicled her omega odyssey, Oprah magazine decided not to publish it. Susan got paid for her efforts—but that wasn’t the point.  Susan wanted to raise awareness of the harmful health effects of eating excess omega-6 fats, and so she approached me with her story.

I was impressed with Susan’s scientific diligence as you shall see in her methodology for a mere subject of n=1. This is an inspiring case study, which shows that it doesn’t take long for an omega-6 fat imbalance to effect health parameters.


The Diet. Susan’s high-omega-6 diet consisted of eating her usual foods and mainly switching to high omega-6 spreads and oils for one-month.  For example, regular mayonnaise (made with soybean-oil) replaced canola-based mayo.  Olive oil-based salad dressings were replaced with a mixture of safflower, sunflower, corn, and soybean oils.   She also replaced her grass-fed dairy products with traditional dairy foods.

Fish was eaten at least twice weekly, because it is an American Heart Association (AHA) recommendation. (Notably, AHA also recommends using omega-6 oils ).

Scientists were recruited to evaluate the effect of eating a high omega-6 diet for 30-days, which included evaluations of fatty acid content of blood cells, body composition, and cardiovascular parameters. 

Fatty Acid Analysis. Blood samples were analyzed for fatty acid content. Doug Bibus, MS, PhDfrom the University of Minnesota, provided a home omega-3 kit for daily blood testing. 

Metabolism and Cardiovascular Indices.   Jeff Volek, RD, MS, PhD, an associate professor in the Human Performance Laboratory at the University of Connecticut, provided the following tests:

  • Body composition evaluation using a state-of-the-art dual-energy X-ray machine to determine the amount, and distribution, of fat and lean tissue.
  • Resting Metabolic Rate (RMR) was evaluated by measuring oxygen consumption for a 30-minute period. (Each liter of oxygen consumed, is the equivalent of about 5 calories.)
  • Flow-Mediated Vasodilation was measured, to evaluate vascular health.
  • Arterial Stiffness was measured by an ultrasound scan.

Results: The results were surprising for only a 30-day evaluation.  Susan’s weight remained unchanged. But there were dramatic changes in her blood fatty acid composition, body fat, arterial function, and body mass composition. During the 30-day period, omega-6 fatty acid was significantly increased, while omega-3 fatty acid content was decreased, as shown in the three following charts:

These fatty acid blood changes also impacted the Omega-3 Index score, which is a blood-based risk factor for predicting heart disease risk. For heart health, the recommended Omega-3 Index is 8% or greater [1].  Susan’s baseline score of 8.3 decreased to 4.7% in just 30 days, as shown below:

While body weight remained the same, body fat increased in the abdominal area by nearly ½-pound.  Fat was also increased in the trunk region, where notably, lean body mass decreased.  Metabolic rate also decreased from 1367 to 1291 calories.

In just 30 days, brachial artery dilation dropped by 22%, a change much larger than the day-to-day variation of this test. The amplitude of this changed surprised everyone involved in this project.  Susan’s arteries were also stiffer, as revealed by the ultrasound scan, which indicates blood vessels are less able to expand and contract.

Discussion: The fact that Susan’s body weight remained the same is important, because it indicates that Susan wasn’t overloading her omega-6 intake to the point of gaining weight, she only changed the type of fat she was eating.

It’s especially notable that although Susan ate fish at least twice weekly, her Omega-3 Index dropped significantly.   This reinforces the notion that merely gobbling fish oil, or eating fish, will not overcome the problem of eating a high omega-6 fat diet.

Japanese researchers discovered a similar phenomenon and called it “Omega-6 Syndrome.” They were puzzled as to why Okinawan inhabitants experienced a sudden and marked rise in chronic health diseases. The answer, the scientists discovered, was Okinawans had inadvertently tripled their omega-6 intake [2] .  Notably, just like Susan, the Okinawans were still eating fish, but it did not protect them from health problems, when eating a higher omega-6 fat diet.

Commentary: Unquestionably, a study with a subject of n=1, does not make for conclusive evidence.  But given the surmounting studies indicating harmful effects from excess dietary omega-6 fats, this case study merits replication with a statistically significant sample size.

Today we eat oils that did not exist 100 years ago, like cottonseed and soybean oils, which are among the top sources of omega-6 fat. Prior to industrialization, no population has eaten the current high levels of omega-6 fat. While omega-6 fat is an essential nutrient (specifically linoleic acid), eating just two slices of whole wheat bread will provide what your body needs. 

Over a decade ago, enough evidence existed to prompt scientists to recommend eating less omega-6 fats [3].  But there is still no public health policy to lower omega-6 to balanced levels of less than 3% of calories, (which is less than 7 grams/day, based on a 2000-calorie diet.) Americans currently eat double this amount.

Just last year AHA urged Americans to make omega-6 fats a part of heart-healthy eating [4], (also see What is the American Heart Association’s Agenda?)

Perhaps, awareness and change will come from public health's “war on obesity”.  Earlier this month, the newswire service AFP, warned that eating the wrong mix of fats can cause obesity, and quoted the lead scientist, "Omega six is like a fat-producing bomb" [5]

If you would like to help bring awareness to this important public health issue, please feel free to post this article on your blogs and social media sites. Also, if you would like to read Susan's full story and access the data described here, (but in more detail), you will find it on Susan’s homepage (left column):

Link to Resources

[1] The Omega-3 Index: a new risk factor for death from coronary heart disease? Prev Med. 2004 Jul;39(1):212-20 .

[2]  Okuyama, H et al. Dietary fatty acids—the n-6/n-3 balance and chronic elderly diseases: excess linoleic acic and relative n-3 deficiency syndrome seen in Japan. (1997); 35(4):409-457 .

[3]  Simopoulos AP, Leaf A, Salem Jr N.Workshop on the Essentiality of and Recommended Dietary Intakes for Omega-6 and Omega-3 Fatty Acids. 1999; 18: 487-489 

[4] Omega-6 fatty acids: Make them a part of heart-healthy eating. DALLAS, Jan. 27, 2009.

[5] Hood, M. Omega imbalance can make obesity 'inheritable': study. (AFP) – Jul 16, 2010.

Copyright © 2010 by Evelyn Tribole, MS, RD  Published at

Rights to Reproduce: As long as you leave it unchanged, you don’t charge for it, and you include the entire copyright statement, you may reproduce this article. Please let us know you have used it by sending a website link or an electronic copy to Etribole at gmail dot com.

DISCLAIMER: The information is intended to inform readers and is not intended to replace specific advice from a health care professional.  Copyright 2010 Evelyn Tribole, MS, RD

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  • July 26, 2010 1:57 PM Ted Hutchinson wrote:
    While it's interesting to see the details of how quickly Susan's omega 3 levels dropped following the change to a higher omega 6 intake we have to remember there are a huge number of cells in the human body. To convert each of those cells back to the omega 3 omega 6 ratio human DNA evolved with will take much longer.
    In my experience going the other way, increasing omega 3 intake decreasing omega 6 seed oils, led to a year on year increased resistance to uvb damage over the last 5 yrs. Perhaps it's fair to say the improvement over the first couple of years was greater than over the last 3 years. While I'm sure improvements in health from reducing omega 6 intake and increasing omega 3 levels will be measurable in the short term (first 3 months) I also think people have to understand for the full effect to be appreciated this has got be be regarded as a long term project, with ongoing improvements year on year to be expected over 5 yrs.
    Reply to this
    1. July 26, 2010 2:21 PM Evelyn Tribole MSRD wrote:
      Your point is well taken.  Unlike changing the oil in your car, which takes minutes----it can take up to 7 years to "change out" the omega-6 fatty acids from the cells in your body.

      It's encouraging to know however, that positive health changes can occur in a matter of weeks. It takes an average of 12 weeks to incorporate omega-3 fats into the cell membrane--a fact not always controlled for in studies.  (I tell my patients it's akin to changing all the light bulbs on the Las Vegas strip--it takes some time!)
      Reply to this
  • July 27, 2010 5:34 PM Evelyn Tribole MS RD wrote:
    In today's news:

    CNRS. "Excessive Intake of Omega 6 and Deficiencies in Omega 3 Induce Obesity Down the Generations." ScienceDaily 26 July 2010. 27 July 2010
    Reply to this
  • July 28, 2010 8:40 AM alfredoe wrote:
    Vary interesting example. I wish you had the triglycerides and HDL cholesterol changes.
    Reply to this
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