Monday, February 28, 2011

High Omega-6/Omega-3 Ratio Increases Prostate Cancer Risk

A recent case-control study shows a relationship between the ratio of omega-6/omega-3 consumed and prostate cancer. No association was found between individual, or what I call absolute, intakes of either omega-3 or omega-6:

A High Ratio Of Dietary N-6/N-3 Polyunsaturated Fatty Acids Is Associated With Increased Risk Of Prostate Cancer, Nutrition Research, January 2011
Our results showed no significant associations between specific n-3 or n-6 PUFA intakes and prostate cancer risk.
Our findings suggest that a high dietary ratio of n-6/n-3 fatty acids may increase the risk of overall prostate cancer among white men and possibly increase the risk of high-grade prostate cancer among all men.
The odds ratios were startlingly high.

Here's a table I made last year that shows omega-6 and omega-3 content of some common foods:

Click to enlarge.

The best way to increase your relative omega-3 is to decrease your omega-6 intake. If you eat a sizable amount of omega-6, then eating more fish or other foods high in omega-3, or taking fish oil, may just increase your overall fat intake without improving your ratio.

Vegetable oils are high in omega-6. As you can see from the chart, nuts, seeds and oils made from them (e.g. corn oil and soy oil) are leading sources of omega-6 in Americans' diets. (The grains themselves, like corn or rice, are not as much of a problem since they are low in fat and provide little omega-6 per serving.)

Note that greens (romaine, broccoli, kale, spinach) generally have more omega-3 than omega-6 and so are excellent ways to improve your ratio. Walnuts on the other hand have more omega-6 than omega-3 and so are not a good way to improve your ratio.

Both omega-3 and omega-6 are polyunsaturated fats. If you take extra omega-3, in pill or food, you are intaking more polyunsaturated fat. These fats have highly-reactive double bonds and oxidize quickly, especially when they meet acids in your stomach. Oxidized fats, and their metabolites, have been shown to increase risk for atherosclerosis and some cancers.

A good ratio to shoot for is 4:1 or less. That's 4 units (or less) of omega-6 for every one unit of omega-3.


RB said...

Looking at the chart it looks rather difficult to obtain a good omega 3 / omega 6 ratio unless ones loads up on beans, flaxseeds, fish and veggies and avoids meats and nuts. Anyone who includes any meat in the diet doesn't seem to have a chance at having a good ratio. Since humans evolved to eat meat as well as plants, does the 1/4 doesn't seem right? It also seems a nutritious source of food, nuts, should be avoided. There must be more to this because things don't seem to add up.

caulfieldkid said...


This is something I've been thinking about too. I think part of the issue is the type of meat that is commonly consumed. Fish don't appear to be a problem as well as a good portion of wild game:

I would be interested in hearing what a sociologist says about our diet 100 years ago. I have a notion that mass/factory produced meat didn't make a regular appearance on the dinner plate (but I can't substantiate that notion).

I also wonder about the macro and micro side of things. These are guidelines for the general public, but we already know that everyone is different (Bix's post on those who don't have cholesterol problems but are more susceptible to colon cancer comes to mind). How does your ancestors diet effect your own? Mr. Rinella talks about this some in this book:

or maybe it was this one (sorry, I can't remember which but both are good reads.):

He discusses certain Native American tribes that had a diet almost exclusively of meat. (It may be worthy to note here that the game they ate appears to follow, roughly, the 4/1 ratio).

We live in an interesting time where we have access to nearly any food imaginable. I believe that's a first. With the luxury comes peril.

Still in love with beans,


Bix said...

Interesting books, shaun. So sad about the buffalo.

I think hunting is more humane than factory farming. The animal gets to live freely, express its natural behaviors, choose a mate, nurture its young, gossip about humans, ostracize nonconformers, and outsmart hunters. The only problem with hunting, for me at least, is there are no organically-fed wild animals roaming my neighborhood. Animals that forage around here consume robust amounts of pesticides, herbicides, and leftover Papa John's pizza. I just don't trust it.

Anonymous said...

Bix, there's still a missing piece in the puzzle. The chart shows how even grass fed, grazed beef has a higher omega6 to 3 ratio, and yet our ancestors undoubtedly ate cattle as part of a main staple. The fact is, we HAD to eat meat for the vitamin b12 and thiamine that was required for proper fetal, and child development. Given that seafood was not always available, animal products were a definite staple of our diet regardless of its omega6/3 ratio.

polyunsaturated fat is also not innately 'bad.' It is healthy and is contained in my nutritious foods such as nuts, avocados, etc...

I think inflammation is the main problem with heart disease. Without inflammation, polyunsaturated and mono unsaturated fats and a larger omega6/3 ratio would not be as problematic.

Bix said...

I don't think nuts and seeds are the problem. In fact, I think diets that include them are better than diets that exclude them. They have beneficial nutrients that make them worth eating.

I think processed foods made with cheap, overly-refined vegetable oils that are high in omega-6 are the problem.

I just looked up potato chips:

3 ounces contain 10062 mg omega-6 and only 160 mg omega-3. That's a 63:1 ratio. That's hard to get back down to 4:1 with the rest of the day's food.

Unknown said...

Walnuts? No, I wouldn't consider them bad. They have a 4-1 (O6-)3) ratio, one just can't over do it. Broccoli is great, but it contains a miniscule amount.

Here's a great abstract about ratios and different diseases:

Bix said...

Good stuff. I'm familiar with Artemis Simopoulos, her writing. She's published a lot and makes great arguments.

In recent years I've come to recognize the importance of getting some (not a lot) long chain omega-3 in the diet - straight up. EPA and DHA are longer chain omega-3s. Our bodies elongate the shorter chain omega-3's, but the extent varies.

Lou said...

"I think processed foods made with cheap, overly-refined vegetable oils that are high in omega-6 are the problem."

Bingo you have hit on the MAJOR factor in both Cancer and CVD. Lose the processed vegetable oils found in processed "food", junk "food" and most other cheap "foods" and you are half way home.

Giulia said...

I find the information very useful! Can I please know where you found the chart on the balance between omega 3 and 6?

Bix said...

Yes, the chart came from here: