Tag Archives: polyunsaturated fat

Polyunsaturated fat, Saturated fat and the AHA

The present paradigm among physicians and cardiologists presents saturated fat as a disease producing component of animal foods. Dietary recommendations include the reduction of saturated fat and replacement with carbohydrates and/or monounsaturated and polyunsaturated fats. In fact, the American Heart Association (AHA) updated its recommendations to increase the consumption of polyunsaturated fats as a percentage of total caloric intake in January 2009.

This was met by protests from three NIH scientists who had done extensive research in the area of fat consumption and health. Those scientists wrote letters to the editor of Circulation, the scientific journal of the AHA. Those protest letters were not published in print but were published on-line (where only geeks like me would find them,  the vast majority of physicians would never lay eyes on them)

The authors of those letters subsequently produced a brilliant study that involved forensic research. They conducted interviews with principal investigators who directed the studies upon which the AHA had based it’s recommendations. They discovered important data that had been collected but not mentioned in those study publications by painstakingly sleuthing multiple sources. They then produced a meta-analysis of the data from the studies. Their meta-analysis was published in the British Journal of Nutrition Dec 2010.

http://www.ncbi.nlm.nih.gov/pubmed/21118617

What they found was astonishing. The AHA had based it’s recommendations on faulty data. A major point of refutation involved  omega 3 fatty acids (fish oil which is arguably cardio- protective) vs omega 6 fatty acids. Both are poly-unsaturated fatty acids (PUFA). The AHA paradigm has been that replacing saturated fat with omega 6 PUFA results in reduction of cholesterol (short term studies) and therefore should reduce heart attacks and stroke. But the studies they used to support their recommendations were not “clean”.

Only three of the nine studies were “pure” omega 6 interventions, which increased omega-6 FA without a concurrent rise in omega-3.

Four of the studies increased both omega 3 and omega 6 PUFA. In one of those four studies the patients were given the equivalent of 16 fish oil capsules per day.

The control diets had an estimated 3% manufactured trans fats in the diet. This unquestionably increases risk of heart attack and creates a confounding factor.

The Omega 6 diets increased the risk of heart disease and death compared to the mixed omega 3 and omega 6 studies. The risk of cardiac death was increased by 28% in the omega 6 diets compared to the mixed diets.

The mixed omega 6 omega 3 diets showed an 8% risk reduction of death from all causes and a 22% risk reduction from cardiac death.

So the AHA had made recommendations that could possibly be harmful and certainly not helpful. Despite this great piece of investigative science, the AHA did not change it’s recommendations.

Since that time Christopher Ramsden and colleagues have published a sequel “to evaluate the effectiveness of replacing dietary saturated fat with omega 6 linoleic acid, for the secondary prevention of coronary heart disease and death”.

http://www.ncbi.nlm.nih.gov/pubmed/23386268

In their summary they stated:

“substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. “

There you have it. The AHA has not withdrawn it’s dietary recommendations to increase n-6 fat despite the compelling evidence to the contrary. This is unfortunately a consistent pattern.

Why would an increase in omega 6 fats and a reduction in saturated fat increase cardiovascular events?

Here is one explanation which is supported by basic science. Omega 6 fats are PUFA (polyunsaturated). PUFA are easily oxidized but saturated fat is not. When PUFA sit in the membrane (outer wall) of LDL particles they become oxidized and the oxidized LDL particle stimulates macrophages (white blood cells) to become foam cells and create plaque in the walls of your arteries. Saturated fats are not easily oxidized. Saturated fats do not contribute to the formation of oxidized LDL.

The AHA encourages us to consume “vegetable oils” (oils made from corn, soy, cottonseed, safflower, etc) instead of saturated fat. The predominant fat in “vegetable oil” is linoleic acid, the major omega 6 fat in the American diet. Linoleic acid is not the hero in this story and saturated fat is not the villain that the AHA portrays it to be.

Having said that, one might ask the following. If PUFA are easily oxidized and omega 3 fats are are also PUFA, then how could omega 3 fats be “cardio-protective” while omega 6 fats are damaging?

Good question. That will be addressed in  future posts.

But before we get to that, there are other data on saturated fats that must be discussed in order to dispel the fear of saturated fat.  That data and discusion will come in the next post.

Go in peace, the post is ended.

Bob Hansen MD