ASBMB Today has a well-written balanced article on the omega-6/omega-3 fatty acid ratio debate written by Rajendrani Mukhopadhyay. A fair amount of it is understandable to non-science majors. The main question is whether the high consumption of omega-6 fatty acids in Western societies is unhealthy.
It’s estimated that throughout most of human evolution, our dietary omega-6/omega-3 ration has been around 3:1 or 2:1. Today, it’s about 15:1, thanks to a large increase in omega-6 consumption. Are our bodies adapted for the lower ratio? A hard-core paleo diet like Dr. Cordain’s aims for that lower ratio.
Both sides of the debate agree that we would probably be better off eating more omega-3 fatty acids, as found in cold-water fatty fish.
I’m an omega-6/omega-3 ratio agnostic at this point. I’ve never studied it in depth, so I have no strong opinion either way.
Here are a couple excerpts from the article to pique your interest:
No one is disputing that we’re eating more omega-6 than our predecessors did. Over the past 100 years, consumption of linoleic acid [an omga-6] has increased dramatically in the U.S., mainly through the use of soybean oil. Soybean oil intake has gone up from being 1 percent of calories in the American diet to as much as 10 percent, according to Hibbeln. Lands, Salem and others contend that the rise, driven by the processed food and agriculture industries, has happened without anyone knowing its effects. “If I were now to try to get permission to change 10 percent of the calories in the U.S. diet, I would need a very large body of data unequivocally proving that it was safe,” says Hibbeln. “No such body of data exists for soybean oil. But it’s in our diet. We’re the experiment. It’s been a very large, uncontrolled intervention.”
Experts like Harris and Willett say this increase has been to our benefit. “We have seen a massive decline in cardiovascular disease mortality and huge increase in life expectancy,” says Willett. “Not all the benefit is due to the increase in linoleic acid, but almost certainly much of it is. It was not an absolute disaster.” But the lipid biochemists counter that it’s not just cardiovascular disease at stake. They say diabetes, obesity and even psychiatric disorders are some outcomes of a diet heavy on omega-6s.
I’ve never before heard anybody credit linoleic acid with a major role in our “huge increase in life expectancy” over the last century. I doubt that’s the case. I vote more in favor of better sewage systems, cleaner water, better hygiene, antibiotics, or improvements in surgery and medical care.
Evolutionary biologist Theodosius Dobzhansky said, “Nothing in biology makes sense except in the light of evolution.” If that’s true, the default position is that lower amounts of omega-6 fatty acid are better than our current high consumption. It’s up to the high-consumption proponents to prove otherwise.
Steve Parker, M.D.
h/t David Despain
PS: Dobzhansky was a Christian, by the way.
PPS: A Twitter reader (@pronutritionist) suggested that the modern Western dietary omega-6/omega=3 ratio is 9.6, not 15:1, citing Amer J Clin Nutr. My source for 15:1 is Journal of Nutrition and Metabolism, vol. 2012, article ID 539426, doi 10.1155/2912/539426, by E. Patterson et al. I admit it’s not a great reference. Cordain’s 2002 book, The Paleo Diet, says 10:1. Maybe it is closer to 10:1. I’m sure there’s lots of inter-person variability.