Sunday, April 10, 2011

US Omega-6 and Omega-3 Fat Consumption over the Last Century

Omega-6 and omega-3 polyunsaturated fats (PUFA) are essential nutrients that play many important roles in the body. They are highly bioactive, and so any deviation from ancestral intake norms should probably be viewed with suspicion. I've expressed my opinion many times on this blog that omega-6 consumption is currently too high due to our high intake of refined seed oils (corn, soybean, sunflower, etc.) in industrial nations. Although it's clear that the quantity of omega-6 and omega-3 polyunsaturated fat have changed over the last century, no one had ever published a paper that attempted to systematically quantify it until last month (1).

Drs. Chris Ramsden and Joseph Hibbeln worked on this paper (the first author was Dr. Tanya Blasbalg and the senior author was Dr. Robert Rawlings)-- they were the first and second authors of a different review article I reviewed recently (2). Their new paper is a great reference that I'm sure I'll cite many times. I'm going to briefly review it and highlight a few key points.

1. The intake of omega-6 linoleic acid has increased quite a bit since 1909. It would have been roughly 2.3% of calories in 1909, while in 1999 it was 7.2%. That represents an increase of 213%. Linoleic acid is the form of omega-6 that predominates in seed oils.

2. The intake of omega-3 alpha-linolenic acid has also increased, for reasons that I'll explain below. It changed from 0.35% of calories to 0.72%, an increase of 109%.

3. The intake of long-chain omega-6 and omega-3 fats have decreased. These are the highly bioactive fats for which linoleic acid and alpha-linolenic acid are precursors. Arachidonic acid, DHA, DPA and EPA intakes have declined. This mostly has to do with changing husbandry practices and the replacement of animal fats with seed oils in the diet.

4. The ratio of omega-6 to omega-3 fats has increased. There is still quite a bit of debate over whether the ratios matter, or simply the absolute amount of each. I maintain that there is enough evidence from highly controlled animal studies and the basic biochemistry of PUFAs to tentatively conclude that the ratio is important. At a minimum, we know that excess linoleic acid inhibits omega-3 metabolism (3, 4, 5, 6). The omega-6:3 ratio increased from 5.4:1 to 9.6:1 between 1909 and 2009, a 78% increase.

5. The biggest factor in both linoleic acid and alpha-linolenic acid intake changes was the astonishing rise in soybean oil consumption. Soybean oil consumption increased from virtually nothing to 7.4% of total calories, eclipsing all sources of calories besides sugar, dairy and grains! That's because processed food is stuffed with it. It's essentially a byproduct of defatted soybean meal-- the second most important animal feed after corn. Check out this graph from the paper:

I think this paper is an important piece of the puzzle as we try to figure out what happened to nutrition and health in the US over the last century.

32 comments:

JLL said...

Interesting that grain consumption seems to have gone down during the last 100 years, I would've thought the opposite.

Perhaps industrial seed oils are a worse problem than grains when it comes to modern diseases?

- JLL

Aravind said...

Hello Stephan,

Did you see the following article in The Atlantic -
http://www.theatlantic.com/business/archive/2011/04/are-grains-making-us-fat/237030/

Kurt Harris was "jousting" with the editor in the comments on some of the incorrect conclusions drawn. If you have the time/desire, it would great for you to provide your valuable input too.

Regards,
Aravind

Sarah Smith said...

Thanks for this post. I've been wondering about omega 3 and 6 quite a bit lately, and whether the ratio is the most important thing to look at. I look forward to seeing your follow-on thoughts in future posts!

Charlie said...

Hmm.

Graph is deceptive. Measures percent of calories as against absolute amount. Measure that against the increase in sugar by pounds

What is the category "fats"?

If I'm correct in remembering, us cvd rates have improved since 1970. Smoking? Better surgical intervention for actute attacks?

john said...

"There is still quite a bit of debate over whether the ratios matter, or simply the absolute amount of each."

It should be tricky since we're generally looking at ratios and amounts in the context of terrible diets. Do any healthy cultures consume [relative to other non-industrials] high pufa through poultry fat or nuts/seeds?

Sam said...

In response to Charlie, I quote from the caption of the figure (Figure 2 in the article). "Fats included shortening, butter, lard, margarine, and beef tallow. Soybean oil was considered separately from other oils because of its disproportionate contribution. Dairy included all milk, buttermilk, condensed milk, cream, sour cream, yogurt, cheese, and eggnog. Butter was not included in the dairy category to avoid double counting."

Aaron Blaisdell said...

Interesting bit of historical research. The graph is difficult for individuals with red/green colorblindness to read. That's why I always prefer the use of dashed lines of various sorts, rather than or in addition to color, to represent different conditions (unfortunately this alternative method can't be applied to stained slides of brain tissue used in neuroscience--never could read those damned things!).

Jack C said...

Shorter telomere length augurs greater risk of mortality and premature mortality in the elderly. Telomere length is inversely associated with linoleic acid intake but not total fat intake. Increased intake of linoleic acid results in increased oxidative stress and inflammation which apparently results in a shorter lifespan.

http://www.ncbi.nlm.nih.gov/pubmed/20219960

Stabby said...

Cheers for the link, Jack.

If we accomplish anything at all it should be to make the populace aware of the evils of high omega 6 oils. Dr. Bill Lands has been trying since the 60s but there is just too much corporate interest. Arg.

Stephan Guyenet said...

Hi JLL,

Yes, I included that part of the graph deliberately because I think it's important to acknowledge. Grain intake was mostly white flour and cornmeal in 1909.

Hi Charlie,

"Fats" means added fats. The USDA database refers to added fats simply as "fats", which is misleading because they don't track total fat disappearance. They don't track the fat content of meat or nuts for example, and dairy fat other than butter is not included in that figure.

That has led to a lot of confusion, including an unfortunate NY Times article that suggested total fat intake has increased dramatically since the 70s. I sent in a letter to the editor attempting to gently correct them, but it didn't get published.

http://wholehealthsource.blogspot.com/2008/08/letter-to-editor.html
http://www.nytimes.com/imagepages/2008/08/03/business/03metrics.graphix.ready.html

Stephan Guyenet said...

PS- regarding the CHD changes over the last 60 years, CHD deaths have decreased but it's not clear that incidence has decreased. There is some evidence from the Framingham cohort that it has, but the rest of the data that I've seen are inconsistent. I think it's plausible that a decline in smoking has decreased CHD incidence, and it's also pretty clear that improved emergency care has contributed to lower CHD death rates.

luc0815 said...

Hi Stephane,
thanks for this important information.
The chart is really difficult to understand without more explanations. Are the colors in the legend actually correct?

Charlie said...

@Stephan; ok, now to confuse things even more -- what is "shortening" in the graph?

RE: CVD; absolutely, smoking+medical technique is a huge difference. And given that the first MI wasn't named until the 1920s -- I think that is when they discovered an ECG -- historical data is hard to pinpoint.

However, if I remember right the US is doing very well vs. rest of developed world on CVD. Very bad on obesity/diabetics, but much better on cholesterol counts.

Emily Deans, M.D. said...

Didn't Gary Taubes suggest the grains disappearance Data was misleading at the beginning of the century because so many people (90%) lived in rural areas - with gardens and chickens and the like that wouldn't show up in the disappearance figures - therefore the purchased grain percentage was misleadingly high? Unless it is an absolute amount or something. Of course, the mental health of folks eating unenriched white flour and corn meal wasn't so terrific...

Todd Hargrove said...

Stephan,

Interesting post. So modern omega 6 to 3 ratios are only 9 to 1? This sounds much lower than various other estimates I have seen mentioned such as 15 to 1 or 20 to 1.

David L said...

Stephan,

I just don't understand where all that soy oil is coming from. Maybe since I eat so little processed food, I don't see much soy oil in my diet. Soy is definitely a big element in animal feed, but I don't understand how the soy oil is getting into the diet outside of, say, mayonnaise. Could you please clue me in?

Mark said...

David,

Walk through the center of your local supermarket and pick up boxes up processed wheat food that the masses buy in droves. You'll see soybean oil in almost everyone (e.g. crackers, cookies, etc.)

Even pasta sauce makers now use soybean oil in most of their sauces to save money instead of purchasing expensive olive oil.

Also, many fast food chains cook their foods with it (e.g. Panda Express, Applebees, etc.)

It's everywhere (unfortunately)

Jack C said...

Stephan,

Is the data shown in the graph based on an assumed constant caloric intake, and if so, what is the caloric intake assumed?

Data from the Institute of Shortening and Edible Oils, which appears to be based on USDA data, states that while total fat consumption increased only slightly between 1970 and 1997, the percentage of calories from fat declined from 43% to 34% between those years due to increased caloric intake.

Might-o'chondri-AL said...
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Might-o'chondri-AL said...
This comment has been removed by the author.
Stephan Guyenet said...

Hi Emily,

Yes, but that strikes me as hand waving. It's possible but I'd like to see some evidence.

Hi Todd,

Yes, the ratios have been exaggerated in a number of papers over the year. There are a lot of loose numbers out there. That being said, there's a lot of variation so there are certainly people out there eating 20:1 or higher.

Hi David L,

Salad dressing, chips, crackers, anything deep fried, restaurant oils, mayo, pastries, vegetable oil, etc. It's in most processed food.

Hi Jack C,

The graph shows food group intake as a percentage of calories, so it scales as calorie intake increases.

Stephan Guyenet said...

Hi Emily,

I found this quote in the USDA document "Major Trends in US Food Supply, 1909-99":

Food disappearance estimates for
animal products—meats, eggs, and dairy products—include that which was produced and consumed on farms and in rural nonfarm and urban households. Annual consumption estimates for both commercial vegetables (fig. 15) and vegetables from home gardens (fig. 16) were made through the early 1970’s. Since then, estimates of home-garden production have been sporadic because of spotty data. Home production of other crop foods like cereal products, caloric sweeteners, and vegetable fats was deemed too little to bother estimating, even in 1909"

Emily Deans, M.D. said...

Thanks Stephan. Have you seen this old paper, "The menace of bleached flour"? I love these old papers...



http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2055083/pdf/brmedj03811-0021.pdf

Dr. B G said...

Emily,

The Mellanby's experiments are great!! (prior to IRB-days where they have studies on puppies and young children)


Stephan,

The gluten protein content of wheat has changed with genetic engineering considerably. I tried to find a 'neat' graph but couldn't locate one (does anyone have one??!)

Wet gluten% is up to 35% in some crops (hard red winter, hard red spring, etc). Market metrics and 'quality' (and ultimately bread making value) are determined now by gluten content. Shocker, eh?

I wonder what it was earlier...?? 5%? soft wheat is 12-15%

-G

Kurt said...

@All

How to maximize your n-6 consumption:

http://top200foods.com/Nutrients/Fatty%20Acids%2018:2%20n-6%20c,c/675/g

Sent to me by a reader just this morning.

HInt: Butter is #161 on the list...

Helen said...

I think increased n-6 consumption is one of the culprits. But I just saw this, one in a small flurry of articles I've seen lately on the systemic, inflammatory effects of air pollution. It seems if we're comparing the past to the present in terms of health, air quality is one of the many factors - some of them non-dietary - that need to be taken into account.

"Polluted Air Leads to Disease by Promoting Widespread Inflammation"
http://www.sciencedaily.com/releases/2011/04/110414131834.htm

Might-o'chondri-AL said...
This comment has been removed by the author.
Anna said...

Mighty Al said:
"what is right under their noses."

Ha, ha, very funny pun. ;-)

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Emily said...

My grandmother grew up in rural West Virginia in the 1920s and told me that she ate mainly 'mush' which was basically cornmeal grits plus whatever they could grow in their garden. Her current grain consumption is lower than when she was young, so that statistic made some sense to me...she's currently 92 and going strong yay grandma!

renes said...

U.S. per capita consumption of salad and cooking oils increased from 21.2 pounds per person in 1980 to 54.3 pounds per person in 2008.


Census: Table 213. Per Capita Consumption of Major Food Commodities: 1980 to 2008

jewiuqas said...

Some plant derived oils contain considerable amounts of omega-3, such being for example linseed oil, and camelina (false flax) oil (53% and 39% of omega-3 respectively!). I wonder if there is any difference between the omega-3 of animal and that of plant origin. Does the plant omega-3 have the same beneficial health effects as fish oil? Is that the same molecule everywhere? Why I am asking this is that for instance some important vitamins have different animal and plant subtypes where usually it is the animal version that is more readily used by the organism. But perhaps fats are simpler than vitamins.