11

votes

Polyunsaturated fats, why are they so bad?

Answered on August 19, 2014
Created April 26, 2010 at 11:49 PM

What are the proven negative effects of linoleic acid consumption? A common theme seems to be that it is converted into arachidonic acid that increases inflammation. Yet most people seem happy to consume large amounts of arachidonic acid itself in meat, eggs and organ meat?

It seems a lot like the way saturated fat was demonised years ago on quite circumstantial and inconclusive evidence. I understand about 3:6 ratios but that is as much about increasing 3 than reducing 6 to nothing. I also understand that linolenic acid intake is very high now but do not see the reason to reduce it to close to zero.

By the way I am not refering to use of sunflower oil or corn oil etc, just good foods like nuts, chicken, pork, olive oil etc.

Why do people seem to be treating linoleic acid (omega 6) and overall polyunsaturated fat intake as so bad?

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 29, 2010
at 06:01 PM

Cont: We don't know which wins among people with low LA intakes, but I think the studies I cited very plausibly show that low LA intake = very good health. It's still an open question, but the good thing about paleo is it gives you a way to break ties -- do what we evolved to do - and we didn't evolve to eat vegetable oils.

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 29, 2010
at 06:00 PM

Cont: We don't know which wins among people with low LA intakes, but I think the studies I cited very plausibly show that low LA intake = very good health. It's still an open question, but the good thing about paleo is it gives you a way to break ties -- do what we evolved to do.

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 29, 2010
at 06:00 PM

True - and that same epidemiological evidence shows that LA consumption lowers CVD risk... But, there is other evidence - Lyon Diet Heart Study (controlled trial) and about a dozen tribal studies -- kitava, etc, that show that very low LA consumption is associated with very good outcomes. There are other possible interpretations of this evidence but I think LA is involved. LA lowers LDL but causes more oxy-LDL. The lowering effect seems to win out among people with high LA intakes.

65125edd5aafad39b3d5b3a8b4a36bb7

(6092)

on April 29, 2010
at 05:52 PM

There was supposedly "very good" epidemiological data showing saturated fat caused CVD. Just saying...

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 09:10 PM

Although, note that the result was only significant for large LDL (i.e., not the kind you necessary need to lower). Anyway, one of the main reasons to worry about LDL in the first place is if they are all oxidized on account of eating too much LA... :)

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 09:08 PM

Good question. LA lowers all kinds of LDL. See this very recent result: http://www.ajcn.org/cgi/content/short/91/5/1195

100fd85230060e754fc13394eee6d6f1

(18696)

on April 27, 2010
at 06:47 PM

Does LA lower good LDL or bad (dense) LDL?

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 03:52 PM

Also, if LA is the bad guy and not arachidonic acid, the argument for buying the more expensive omega 3 eggs disappears. They have a tiny bit less ARA but a lot more LA. They also have more n-3s. However, the extra n-3s isn't worth the LA, since fish oil can provide the same n-3 with much less LA.

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 03:50 PM

If you look at this first study I cited, the title indicates that LA does alter plasma levels of various long chain PUFAs. I don't have access to the full paper and the abstract doesn't discuss the results announced in the title, oddly. I agree this subject is poorly understood, but it does seem that arachidonic acid may not be the bad guy. I just don't think that exonerates LA, however. That said, consumption of nuts and other natural sources of LA, like avocados probably may not be that bad. The !kung seem to do ok on a high mongongo nut diet...

0bc6cbb653cdc5e82400f6da920f11eb

(19235)

on April 27, 2010
at 09:53 AM

It is a complex subject. There just doesn't see clear evidence yet that the negative effects of excessive and unnaturaly high comsuption of corn oil etc apply to more moderate intakes, such as the 6 grams in my portion of almonds.

0bc6cbb653cdc5e82400f6da920f11eb

(19235)

on April 27, 2010
at 09:34 AM

True however he is talking about the use of industial seed oils. A more moderate intake of LA balanced with some ALA prevented the obesity in the mice. This effect could just be the poor ratio rather than the total LA? A good ratio would be very hard to achieve eating seed oils.

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3 Answers

6
0a8f18c1bf567443a481a7fd40b3777d

(164)

on April 27, 2010
at 02:25 AM

In my opinion, the best reason for being suspicious of excessive consumption of linoleic acid (LA) is that it is unnatural. There is decent epidemiological data showing that people that eat very low LA diets do very well.

The most common mechanistic argument is that excessive LA leads to excessive arachidonic acid (ARA), which is a precursor for inflammatory eicosanoids. That theory is losing support as new studies don't support it. For example, see this recent study. And, here's another recent study showing that LA leads to less, not more, ARA. Also, ARA derived eicosanoids are necessary for healing and mucosal defense (both of which reduce inflammation long-term) and at least one ARA derived family of eicosanoids are anti-inflammatory mediators -- the lipoxins. Maybe this is why eggs have never been shown to be bad, despite their high ARA content.

Another mechanistic argument against excessive consumption of LA is that it depletes the body of antioxidants and the resulting oxidative damage produces disease.

On the other hand, there are mechanistic arguments that support consumption of LA. LA lowers LDL cholesterol for example. LA may also crowd out longer chain PUFAs from cell membranes, leading to membranes that are more resistant to oxidation, potentially leading to increased lifespan...

Although we may not know why yet, I think excessive consumption of LA is very likely bad. It may be that eicosanoid biology is not as simple as many assumed and the proper balance, whatever it is supposed to be, is thrown off by excessive consumption of LA. Or, LA may be bad for entirely other reasons.

100fd85230060e754fc13394eee6d6f1

(18696)

on April 27, 2010
at 06:47 PM

Does LA lower good LDL or bad (dense) LDL?

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 03:50 PM

If you look at this first study I cited, the title indicates that LA does alter plasma levels of various long chain PUFAs. I don't have access to the full paper and the abstract doesn't discuss the results announced in the title, oddly. I agree this subject is poorly understood, but it does seem that arachidonic acid may not be the bad guy. I just don't think that exonerates LA, however. That said, consumption of nuts and other natural sources of LA, like avocados probably may not be that bad. The !kung seem to do ok on a high mongongo nut diet...

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 29, 2010
at 06:00 PM

True - and that same epidemiological evidence shows that LA consumption lowers CVD risk... But, there is other evidence - Lyon Diet Heart Study (controlled trial) and about a dozen tribal studies -- kitava, etc, that show that very low LA consumption is associated with very good outcomes. There are other possible interpretations of this evidence but I think LA is involved. LA lowers LDL but causes more oxy-LDL. The lowering effect seems to win out among people with high LA intakes.

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 29, 2010
at 06:00 PM

Cont: We don't know which wins among people with low LA intakes, but I think the studies I cited very plausibly show that low LA intake = very good health. It's still an open question, but the good thing about paleo is it gives you a way to break ties -- do what we evolved to do.

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 09:10 PM

Although, note that the result was only significant for large LDL (i.e., not the kind you necessary need to lower). Anyway, one of the main reasons to worry about LDL in the first place is if they are all oxidized on account of eating too much LA... :)

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 03:52 PM

Also, if LA is the bad guy and not arachidonic acid, the argument for buying the more expensive omega 3 eggs disappears. They have a tiny bit less ARA but a lot more LA. They also have more n-3s. However, the extra n-3s isn't worth the LA, since fish oil can provide the same n-3 with much less LA.

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 27, 2010
at 09:08 PM

Good question. LA lowers all kinds of LDL. See this very recent result: http://www.ajcn.org/cgi/content/short/91/5/1195

0bc6cbb653cdc5e82400f6da920f11eb

(19235)

on April 27, 2010
at 09:53 AM

It is a complex subject. There just doesn't see clear evidence yet that the negative effects of excessive and unnaturaly high comsuption of corn oil etc apply to more moderate intakes, such as the 6 grams in my portion of almonds.

65125edd5aafad39b3d5b3a8b4a36bb7

(6092)

on April 29, 2010
at 05:52 PM

There was supposedly "very good" epidemiological data showing saturated fat caused CVD. Just saying...

15d23403fb836f2b506f4f3ad2c03356

(1219)

on April 29, 2010
at 06:01 PM

Cont: We don't know which wins among people with low LA intakes, but I think the studies I cited very plausibly show that low LA intake = very good health. It's still an open question, but the good thing about paleo is it gives you a way to break ties -- do what we evolved to do - and we didn't evolve to eat vegetable oils.

3
06d21b99c58283ce575e36c4ecd4a458

(9948)

on April 27, 2010
at 03:33 AM

Stephan has a posting from last Friday about LA and evidence that LA appears to cause generational obesity in mice after only three generations.

http://wholehealthsource.blogspot.com/2010/04/do-seed-oils-cause-multi-generational.html

Dr Harris is definitely anti-linoleic acid....as is Dr Eades.

I think I'll stick with good old saturated fat in my beef, my coconut oil, my butter, my salmon.

0bc6cbb653cdc5e82400f6da920f11eb

(19235)

on April 27, 2010
at 09:34 AM

True however he is talking about the use of industial seed oils. A more moderate intake of LA balanced with some ALA prevented the obesity in the mice. This effect could just be the poor ratio rather than the total LA? A good ratio would be very hard to achieve eating seed oils.

2
Bdcb2101fd3f1853cfd645094d8ad086

on April 27, 2010
at 01:15 AM

I think this page is interesting:

http://www.thepaleodiet.com/nutritional_tools/fats.shtml

Here's a quote from it:

"The typical western diet is overloaded with omega 6 fatty acids and contains insufficient omega 3 fatty acids. The current ratio of omega 6 to omega 3 fatty acids in the U.S. diet is about 10:1 whereas in hunter-gatherer diets it is closer to 2:1. This dietary imbalance in fatty acids (excessive omega 6 and insufficient omega 3) is a fundamental underlying cause of many chronic diseases including cardiovascular disease, many cancers, most inflammatory diseases, and many psychological disturbances."

That's not backed up with data but it's "from the horse's mouth."

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