Tuesday, June 14, 2011

Feature Article: Saturated Fats: Harmless After All?

The impact of saturated fat on health is a controversy that has been brewing for some time in the field of nutrition. Early research based on animal investigations, ecological observations and controlled feeding studies looking at serum cholesterol supported a major, negative effect of saturated fat on risk of coronary heart disease. 

More recently, there has been some research that may call this into question.  For example, certain classes of saturated fats have been shown to have different effects on our health than others. Furthermore, saturated fat has been shown to be more or less harmful depending on what you eat in its place.  For years, proponents of low carb and paleo diets have been saying that saturated fat is mostly harmless and that the real enemy is carbohydrates.  Some people even take coconut oil (which is a saturated fat) as a health supplement.  So what’s the story here?  Is saturated fat as bad for you as we thought or can you feel free to load up on butter and steaks without risking your heart?  Let’s clear the air.

What Are Saturated Fats?
Saturated fats are fats that contain no double bonds.  All of their carbons are saturated with hydrogen.  They are found, for the most part, in animal products.  Sources of saturated fat include butter, cheese, whole milk, steak, bacon, hamburgers, pepperoni and other fatty meats.  There are also a couple of vegetable sources of saturated fats, most notably coconut oil and palm oil. 

Symposium On Health Effects Of Saturated Fat
In light of the recent questions concerning saturated fats, an expert panel was put together to weight the evidence.  There were some pretty impressive researchers on this panel, including Harvard’s Dr. Walter Willett and Dr. Frank Hu.  The members of the panel reviewed the literature and came up with a consensus opinion on the health effects of saturated fat.  They published their findings in the American Journal of Clinical Nutrition (Reference 1).

Here are some of the key findings:
1) The risk of heart disease is decreased when polyunsaturated fats replace saturated fat in the diet.  For every 1% of energy from saturated fats that are replaced with polyunsaturated fat, the risk of heart disease is reduced by 2-3%.  This is mostly due to the lowering of LDL cholesterol.

2) No clear benefit has been shown for substituting carbohydrates for saturated fat.  However, this may be due to the fact that so much of the carbohydrate consumed in the US is refined and high glyemic load.  These types of carbs tend to lower HDL cholesterol and raise triglycerides.  Evidence is suggestive that replacing saturated fat with low glycemic load carbohydrates significantly reduces risk of heart disease.

3) Replacing saturated fat with refined carbohydrates decreases HDL and LDL particle size (smaller LDL particles are more atherogenic than larger ones) and increases triglycerides.  These changes are quite harmful when it comes to risk of heart disease.

4) It is difficult to tell the effects of monounsaturated fats because in the US, a large percentage of monounsaturated fat is consumed in the form of beef and dairy.   Having said this, the research is suggestive that replacing saturated fat with monounsaturated fat will reduce risk of heart disease.

5) Individual saturated fats have different physiological effects.  Stearic acid tends to be less harmful than other types of saturated fat.   Regarding cholesterol raising effects, stearic acid appears to be neutral where other saturated fats (12:0, 14:0 and 16:0) raise LDL and HDL cholesterol.  C-14 appears to have the most negative effect.

6) There is not enough evidence to judge if short and medium chain saturated fats are harmful.

Take Home Message
So, at the end of the day, saturated fat is still pretty bad for you and it's a good idea to limit it in your diet.  If you replace saturated fat with polyunsaturated fats or monounsaturated fats your risk of heart disease is reduced significantly.  You’ll find these types of fats in vegetable oils, nuts, seeds and avocados.  If you replace saturated fat with low glycemic carbohydrates, it looks like you will also reduce your risk of heart disease.  On the other hand, if you replace saturated fats with the wrong type of carbs like white bread, pasta, white rice and sugar, you may actually be worse off.   The take home message is that the wrong type of dietary carbohydrate is as harmful as the wrong type of dietary fat.  If you’ve read my book or work with me privately, this is old news to you!

Reference
1) The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: Where does the evidence stand in 2010? The American Journal Of Clinical Nutrition 2011;93:684-88.

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