The n3:n6 Omega Ratio is Challenged

[dustinlima]

http://www.ncbi.nlm.nih.gov/pubmed/15630029
full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1201401/


Interplay between different polyunsaturated fatty acids and risk of coronary heart disease in men.

BACKGROUND: Consumption of polyunsaturated fatty acids (PUFAs) may reduce coronary heart disease (CHD) risk, but n-6 PUFAs may compete with n-3 PUFA metabolism and attenuate benefits. Additionally, seafood-based, long-chain n-3 PUFAs may modify the effects of plant-based, intermediate-chain n-3 PUFAs. However, the interactions of these PUFAs in relation to CHD risk are not well established.

METHODS AND RESULTS: Among 45,722 men free of known cardiovascular disease in 1986, usual dietary intake was assessed at baseline and every 4 years by using validated food-frequency questionnaires. CHD incidence was prospectively ascertained. Over 14 years of follow-up, participants experienced 218 sudden deaths, 1521 nonfatal myocardial infarctions (MIs), and 2306 total CHD events (combined sudden death, other CHD deaths, and nonfatal MI). In multivariate-adjusted analyses, both long-chain and intermediate-chain n-3 PUFA intakes were associated with lower CHD risk, without modification by n-6 PUFA intake. For example, men with > or = median long-chain n-3 PUFA intake (> or =250 mg/d) had a reduced risk of sudden death whether n-6 PUFA intake was below (<11.2 g/d; hazard ratio [HR]=0.52; 95% confidence interval [CI]=0.34 to 0.79) or above (> or =11.2 g/d; HR=0.60; 95% CI=0.39 to 0.93) the median compared with men with a < median intake of both. In similar analyses, > or = median intake of intermediate-chain n-3 PUFAs (> or =1080 mg/d) was associated with a reduced total CHD risk whether n-6 PUFA intake was lower (HR=0.88; 95% CI=0.78 to 0.99) or higher (HR=0.89; 95% CI=0.79 to 0.99) compared with a < median intake of both. Intermediate-chain n-3 PUFAs were particularly associated with CHD risk when long-chain n-3 PUFA intake was very low (<100 mg/d); among these men, each 1 g/d of intermediate-chain n-3 PUFA intake was associated with an approximately 50% lower risk of nonfatal MI (HR=0.42; 95% CI=0.23 to 0.75) and total CHD (HR=0.53; 95% CI=0.34 to 0.83).

CONCLUSIONS: n-3 PUFAs from both seafood and plant sources may reduce CHD risk, with little apparent influence from background n-6 PUFA intake. Plant-based n-3 PUFAs may particularly reduce CHD risk when seafood-based n-3 PUFA intake is low, which has implications for populations with low consumption or availability of fatty fish.

----------------------
http://www.ncbi.nlm.nih.gov/pubmed/17876199
full text: no access


The role of dietary n-6 fatty acids in the prevention of cardiovascular disease.

n-6 Fatty acids, like n-3 fatty acids, play essential roles in many biological functions. Because n-6 fatty acids are the precursors of proinflammatory eicosanoids, higher intakes have been suggested to be detrimental, and the ratio of n-6 to n-3 fatty acids has been suggested by some to be particularly important. However, this hypothesis is based on minimal evidence, and in humans higher intakes of n-6 fatty acids have not been associated with elevated levels of inflammatory markers. n-6 Fatty acids have long been known to reduce serum total and low-density lipoprotein cholesterol, and increases in polyunsaturated fat intake, mostly as n-6 fatty acids, were a cornerstone of dietary advice during the 1960s and 1970s. In the United States, for example, intake of n-6 fatty acids doubled and coronary heart disease (CHD) mortality fell by 50% over a period of several decades. In a series of relatively small, older randomized trials, in which intakes of polyunsaturated fat were increased (even up to 20% of calories), rates of CHD were generally reduced. In a more recent detailed examination of fatty acid intake within the Nurses' Health Study, greater intake of linoleic acid, up to about 8% of energy, has been strongly related to lower incidence of myocardial infarction or CHD death. Because n-3 fatty acids were also related inversely to risk of CHD, the ratio was unrelated to risk. n-6 Fatty acids reduce insulin resistance, probably by acting as a ligand for peroxisome proliferator-activated receptors-gamma, and intakes have been inversely related to risk of type 2 diabetes. Adequate intakes of both n-6 and n-3 fatty acids are essential for good health and low rates of cardiovascular disease and type 2 diabetes, but the ratio of these fatty acids is not useful. Reductions of linoleic acid to "improve" this ratio would likely increase rates of cardiovascular disease and diabetes.

[Ransom17]

http://www.ncbi.nlm.nih.gov/pubmed/15630029
full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1201401/



----------------------
http://www.ncbi.nlm.nih.gov/pubmed/17876199
full text: no access

The idea of a good "ratio" between n-3/n-6 fats is a matter of controlling inflammation, along with many other factors. Omega 6 fats are a pro-inflammatory fat. We get so much more n-6 fats in our diet than our bodies can use, and many people literally have pounds of it stored in their bodies. We know that inflammation is an essential part of health, and we would die without that mechanism, but the skewed ratio (20-30x n-6 to n-3 in some cases) DOES in fact cause a net-inflammation state. Some people with autoimmune issues need to reduce that as much as possible until they are at least balanced out. I don't care what any epidemiological studies might show in terms of correlation here, there is a mechanism that can be studied and that is scientific proof enough. You probably already know the bulk of this information if you're making a post like this, but here's a good read anyway (the first one I could find at least)
http://www.direct-ms.org/pdf/NutritionFats/Yehuda%20Omega%203%206%20ratio.pdf

[dustinlima]

The idea of a good "ratio" between n-3/n-6 fats is a matter of controlling inflammation, along with many other factors. Omega 6 fats are a pro-inflammatory fat. We get so much more n-6 fats in our diet than our bodies can use, and many people literally have pounds of it stored in their bodies. We know that inflammation is an essential part of health, and we would die without that mechanism, but the skewed ratio (20-30x n-6 to n-3 in some cases) DOES in fact cause a net-inflammation state. Some people with autoimmune issues need to reduce that as much as possible until they are at least balanced out. I don't care what any epidemiological studies might show in terms of correlation here, there is a mechanism that can be studied and that is scientific proof enough. You probably already know the bulk of this information if you're making a post like this, but here's a good read anyway (the first one I could find at least)
http://www.direct-ms.org/pdf/NutritionFats/Yehuda%20Omega%203%206%20ratio.pdfI'll read that review from 2003 a little bit later, but in the mean time I speculate that the skewed ratio in today's diet comes primarily from a lack of omega-3 intake. Yes, there can also be large amounts of omega-6 intake. But I think the mass public who have to be told by newscasters to eat fish twice a day a certainly not getting any omega-3's there, or from plants. Anyway, this lack of n-3 skews this ratio which could make for a potentially inaccurate causation. Like the final line of the second study posted, it would probably be better to starting consuming omega-3's in addition to, not limiting, omega-6's.

[cadre]

What I take from this is more that n-3 is important in reducing chd risk, not necessarily that the ratio is unimportant.

The ratio is very much skewed in the direction of n-6 in most diets today. I'll have to read the rest of the study but I'm curious how well they controlled all of the variables in the first study. My understanding is that people who get more n-3 from their diet also tend to be healthier because they generally eat better and exercise which would exaggerate the reduced chd risk (huge generalization, I know).

Is it still accepted that the same enzymes act on n-6 and n-3 so there would be a choke-point if too much?

[dustinlima]

Is it still accepted that the same enzymes act on n-6 and n-3 so there would be a choke-point if too much?I have heard that there is competition in the body between these fats, which can sort of support the ratio idea. Will look into this.

[cadre]

I have heard that there is competition in the body between these fats, which can sort of support the ratio idea. Will look into this.

I remembered my book incorrectly, what it actually says is "because the omega-6 and omega-3 fatty acids compete for the same enzymes to make arachidonic acids and EPA and to make eicosanoids, the body needs these long-chain polyunsaturated fatty acids from the diet to make eicosanoids in sufficient quantities" (Rolfes, Clinical Nutrition). So I was close, I would imagine that the ratio does play a role here but I don't know much about eicosanoids (yet).

[Koznasty]

Appears that what is being said is that as long as you meet or exceed the requirement for Omega-3s (including the ESSENTIAL fatty acids EPA/DHA), the 3:6 ratio is health-irrelevant.

I don't believe this is entirely true. Though I don't think the 3:6 ratio is a cause of health issues in and of itself, it could be a decent barometer of potential health issues.

In other words, people aren't unhealthy BECAUSE their 3:6 ratio is heavily skewed to Omega-6s. Rather, they are unhealthy because they eat tons of heavily-processed junk (think burgers, fries, and shakes) which...aha aha...just so happen to contain a lots of Omega-6s and little/no Omega-3s.

So, IMO, an Omega-6 slanted 3:6 ratio doesn't cause heart attacks, but it may indicate nutritional behavior patterns that would predispose somebody to them. Along those lines, people who consume a lot of Omega-3s probably do so because they are the health-types who watch their weight and diet anyway...think about it...salmon, cod, and walnuts are things you kind of have to seek out, they're not common ingredients in your Doritos or Cokes or whathaveyou.

Of course, there's also the concept of relativity, which makes this whole study's conclusion that relying on a ratio isn't a good idea sort of a "DUH" type of thing. (Imagine consuming 10000g of Omega-3s a day and 1000g of Omega-6s; the ratio itself is obviously meaningless if it would indicate "healthy", even though you'd clearly be a walking lard-ass eating that much day in and day out).