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.
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.
I was at the TEDx talk at Harvard last year, and Willett is *very* blase about the excess omega 6 issue and *very* confident in observational data and statistical wizardry to account for confounders. I still don’t see how he comes up with the increase in omega 6 correlating with less heart disease. Omega 6 is a marker for processed food. That means that statistically he is taking out the processed food snack eaters and comparing only a small group of high omega 6 eaters… the salad and poultry crowd who likely exercise and walk their dogs and go sailing and eat plenty of omega 3.
That said, I have looked into the omega 6 issue in some detail (though it quickly becomes very tiresome as it is exceedingly complicated and I am no lipid researcher), and there is some evidence that gallons of omega 6 will downregulate some of the inflammatory pathways, and that sufficient omega 3 will definitely ameliorate many of the downsides of gallons of O6.
All told, I agree with you, and I’m suspicious of PUFAs making up large amounts of the adipose tissue from a straight up biochemical perspective (rancidity). I’m going to avoid them outside natural sources such as fish, poultry and a few nuts, and stick to the natural MUFAs and saturated fats for cooking.
WW has been a PUFA guy for as long as I can remember. Like here: http://www.ncbi.nlm.nih.gov/pubmed/17876199…other studies support him, btw…If omega-6 FA is an endogenous PPAR-gamma ligand (and preferentially so, with the western diet FA composition), then this could be a plausible pathway to both improved metabolic health (relatively speaking – a big relative to be sure) AND obesity, as this nuclear hormone receptor is the key regulator in adipogenesis …http://www.ncbi.nlm.nih.gov/pubmed/8001151. – Larsen’s study brings the point home: http://www.ncbi.nlm.nih.gov/pubmed/12586994 but Fonseca’s study showed that energy storage related weight gain per se, as a subsequent consequence of exogenous TZD (also a PPAR-gamma agonist) is not inevitable if exercise and low calorie diet is maintained…http://www.ncbi.nlm.nih.gov/pubmed/14606983…
In any case, I still think any studies on crop and their derivatives need to rule out GMO, so we (or perhaps just me, lol!) can all move forward.
On a more practical note, obtaining fish-sourced naturally derived omega-3 FA from say, wild caught Atlantic salmon or trout is becoming exceeding rare AND expensive. Other great fish sources of Omega 3 FA’s (mackeral, tuna, etc..) and you are picking your poison, as one has to consider the environmental contaminants. Farmed fish eat GMO corn and soy.
It’s all still quite a mess…
right but omega6s are the precursors for endocannabinoids and have been shown (in mice) to markedly increase endocannabinoids and obesity with increase in % of linoleic acid in the diet… omega3 in a reasonable amount can counteract that…
Ray Medina has just blogged about a very recent study in rats finding that an n-6 PUFA diet markedly increased intestinal permeability versus a similar SFA diet.
So, the outline is: Dense and acellular starches and sugars fuel the generation of problematic PAMPs (including LPS) from microbiota in the small intestine. (See the Steve’s previous post on Ian Spreadbury’s hypothesis.) Grain peptides, refined n-6 oils, and insufficient butyrate-promoting prebiotic fiber result in increased gut permeability. PAMPs translocate through the leaky gut into the lymphatic system and into circulation, and the process can be promoted by ongoing digestion of fats of almost any kind. Inflammation occurs in response to the circulating PAMPs, and the inflammatory products interfere with leptin signaling and possibly the signaling of various other hormones.
Satiety is hosed, the sympathetic nervous system promotes consumption, and the metabolic cascade begins.
That is a nice, just-so story. Perhaps it is even correct and central.
Good summary g2sb. Thanks for the links, too.