Tuesday, February 5, 2013

Linoleic Acid, Heart Disease, And "Experts"

British Medical Journal: "Study raises questions about dietary fats and heart disease guidance." Indeed it does:
Death rates continue to diverge with time!

"Dietary advice about fats and the risk of heart disease is called into question on bmj.com today as a clinical trial shows that replacing saturated animal fats with omega-6 polyunsaturated vegetable fats is linked to an increased risk of death among patients with heart disease...."

"...Advice to substitute vegetable oils rich in polyunsaturated fatty acids (PUFAs) for animal fats rich in saturated fats to help reduce the risk of heart disease has been a cornerstone of dietary guidelines for the past half century. The most common dietary PUFA in Western diets is omega-6 linoleic acid (n-6 LA for short)...."

"...An in-depth analysis of the effects of linoleic acid on deaths from coronary heart disease and cardiovascular disease has not previously been possible because data from the Sydney Diet Heart Study - a randomised controlled trial conducted from 1966 to 1973 - was missing.

"But now, a team of researchers from the US and Australia have recovered and analysed the original data from this trial, using modern statistical methods to compare death rates from all causes, cardiovascular, and coronary heart disease.

"...The results show that the omega-6 linoleic acid group had a higher risk of death from all causes, as well as from cardiovascular disease and coronary heart disease, compared with the control group....

"...In an accompanying editorial, Professor Philip Calder from the University of Southampton says the new analysis of these old data “provides important information about the impact of high intakes of omega 6 PUFAs, in particular linoleic acid, on cardiovascular mortality at a time when there is considerable debate on this question.”

"Calder says the findings argue against the "saturated fat bad, omega 6 PUFA good" dogma and suggest that the American Heart Association guidelines on omega-6 PUFAs may be misguided. They also "underscore the need to properly align dietary advice and recommendations with the scientific evidence base."

Sounds like a fine idea. This is what the Paleo community has been trying to do for years.

Stephen Guyenet had this covered years ago:
"...But it gets even better. The intervention group reduced their omega-6 linoleic acid intake to 3.6% of calories, below the critical threshold of 4%. As I described in my recent post on eicosanoid signaling, reducing linoleic acid to below 4% of calories inhibits inflammation, while increasing it more after it has already exceeded 4% has very little effect if omega-3 is kept low*. This is a very important point: the intervention group didn't just increase omega-3. They decreased omega-6 to below 4% of calories. That's what sets the Lyon Diet-Heart trial apart from all the other failed diet trials.

After five years on their respective diets, 3.4% of the control (prudent diet) group and 1.3% of the intervention ("Mediterranean") group had died, a 70% reduction in deaths. Cardiovascular deaths were reduced by 76%. Stroke, angina, pulmonary embolism and heart failure were also much lower in the intervention group. A stunning victory for this Mediterranean-inspired diet, and a crushing defeat for the prudent diet!
So just to sum it up: the "experts" have been giving us the wrong advice for decades.

Thanks to Jamie Scott on Twitter.

P.S. Dr. Briffa, a cardiologist, covers this study as well: "New data from old study reveals that reducing saturated fat in favour of ‘vegetable’ oils increases risk of heart attack and can have fatal consequences."

P.P.S. Adele Hite (one of the few Registered Dieticians you should actually be listening to) has a great post:
"Although the switch to safflower oil did lower total cholesterol, these reductions didn’t help those participants live any longer than those who kept eating saturated fat. In fact, as the authors note, “the increased risk of death in the intervention group presented fairly rapidly and persisted throughout the trial.” (Hmm. Maybe this whole “cholesterol lowering” thing isn’t as important as we thought.)"
I came to the conclusion quite a while ago that what caused fatty-liver disease was not alcohol or sugar, but linoleic acid. You liver can tolerate high amounts of alcohol, for instance, if you are eating a high saturated-fat, low linoleic acid diet.

One of the paradoxes of medical science is why populations like the French or the Kitivans can smoke like chimneys and not get heart disease at the same rates that Americans do. This study provides a clue that resolves the paradox:
"Furthermore, the authors go on to point out that the relationship between linoleic acid consumption and increased mortality was particularly robust in smokers and drinkers, “suggesting that diets high in n-6 [linoleic acid] may be particularly detrimental in the context of oxidative stress induced by smoking and alcohol."
The toxin may not be tobacco, but linoleic acid, which seems to impair the body's ability to heal itself. Both the Kitivans and the French traditionally eat low levels of linoleic acid. (I'm not endorsing smoking, btw, but observing a telling correlation.) I suspect this also explains why the Kitivans, but not the Indians, can get away with eating a high-carbohydrate diet without the associated negative side-effects.

Here's the link to the full study.