April 23, 2013
One of the newest and highly controversial debates surrounds the question of whether the omega6:omega3 ratio (6:3) has a significant impact on health by inflammation, cardiovascular disease (CVD), and brain disorders. For those of you that are unaware, o6 is dominant in vegetable oils, nuts, flaxseed, etc.
Studies Linking 6:3 to Inflammation and CVD
Here is a review of many studies which concludes that omega-6 (o6) is associated with inflammation, blood clotting, constriction of blood vessels, increases in blood viscosity, and decreases in bleeding time. Omega-3 (o3), on the other hand, is linked to the opposite. It also notes how originally humans were consuming a ratio of 1-2:1 (6:3), whereas now people consume 20-30:1.
Here is a cohort study which examined the effects of o3 and o6 on hemodialysis patients. Their results indicated the following: “Higher dietary omega-6 to omega-3 ratio appears to be associated with both worsening inflammation over time and a trend toward higher death risk in hemodialysis patients.” However, they also acknowledge that additional studies are needed.
A comprehensive review of many human studies lists the following outcomes:
- O6 increases LDL oxidation, decreases HDL, and also worsens clotting of the arteries.
- O6 inhibits absorption of EPA, an o3 fatty acid.
- As the ratio of 6:3 lowers, so does platelet aggregation – a precursor for clotting.
- A study of over 1,100 persons observed a correlation between lower 6:3 ratio and decreased inflammation markers.
- O3 suppresses inflammatory gene expression, whereas o6 does not.
- In people that are susceptible to thickening of arterial walls, o6 works to promote this inflammation, whereas o3 fights it. Direct Source.
- Clinical intervention studies link 6:3 ratio to inflammation markers, CVD, cancers, asthma, and other disorders. Too many sources to list: refer to cited review and read about the clinical studies.
Studies Refuting Omega-6’s Impact on Inflammation and CVD
A science advisory (review of evidence) from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention.
On the issue of inflammation: Basically, arachidonic acid (AA), which is an o6 fatty acid, is a substrate for the production of all kinds of eicosanoids (signaling molecules in the body). Some of which are pro-inflammatory, pro-aggregatory, and pro-constriction of arterial walls. Others serve to do the exact opposite. They cite 5 studies to confirm these findings, and then continue to cite another 9 human trials which refute the idea that AA and o6 are associated with increased inflammation markers and risk for CVD.
The authors go on to investigate o6’s effects on cholesterol, citing 7 studies which concluded that increased consumption of o6 is associated with significantly favorable effects on cholesterol.
Finally, they refer to 9 studies on randomized control trials on the association between polyunsaturated fats and CVD. The authors acknowledge that the studies had severe limitations; however, a meta-analysis along with those trials reported that replacing saturated fat with polyunsaturated fats reduces the risk of CVD, specifically coronary heart disease, by 24-45%. They do not isolate o6 alone as the cause and the authors admitted this.
Studies Examining 6:3’s Role in Brain Disorders
“In major depression, all studies revealed a significant decrease of the polyunsaturated omega 3 fatty acids and/or an increase of the omega 6/omega 3 ratio in plasma and/or in the membranes of the red cells. In addition, two studies found a higher severity of depression when the level of polyunsaturated omega 3 fatty acids or the ratio omega 3/omega 6 was low.” Source
This review examines the importance both o6 and especially o3 play in brain function. The author does not point the finger specifically at o6 and actually acknowledges that AA plays a significant role. The review mainly communicates that many brain disorders are derived from a lack of sufficient essential fatty acids in the diet. The emphasis lies within the need for o3, but o6 and o9 are important as well.
Lastly, here is a human study which concludes that diets with a high 6:3 ratio may enhance the risk for depression and other inflammatory diseases.
Much is still unknown about the significance of the 6:3 ratio and o6’s independent role in the human body, mainly because of limitations on the studies conducted thus far. When viewing all the evidence currently available, it would seem that aiming for a ratio similar to our ancestors (1:1) would be ideal. Even if you are not convinced that o6 should be reduced, you certainly should be making sure to increase o3 by significant amounts.