Scientific Evidence and the Role of Dietary Fats and Carbohydrates in Heart Disease

Dear Dr. B: In your Feb 1, 2011 article, you say that data indicate dietary cholesterol has little effect on blood serum cholesterol levels. I wonder if you could send me references for this. I’m having a debate with a friend and mentioned this, but he doesn’t believe it.

Answer: Finding a reference is not difficult these days. You just have to Google your question and you will find thousands of references. The difficult part is to know which reference is reliable. When I do my research, I generally look at several articles and find reliable scientific information from different sources.

You can find an excellent article on this subject in the American Journal of Clinical Nutrition (April 2011 vol. 93 no. 4 684-688) titled: The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: where does the evidence stand in 2010?

The old hypothesis was that dietary fat raises blood cholesterol which eventually leads to atherosclerosis (hardening of the arteries) and coronary artery disease. This hypothesis was based on research done before we knew anything about the dangers of trans fats.

Now the research has confirmed that heart disease risk rises if there is a high concentration of bad cholesterol (LDL) in our blood and the risk is reduced if there is a high concentration of good cholesterol (HDL) in our blood. But what is poorly understood is the link between dietary fat and high blood cholesterol level.

What do we know about the role of dietary fats and carbohydrates?

-Eating saturated fats – SFs – (found in beef, pork, lamb, dairy products and tropical oils such as palm oil, palm kernel oil, and coconut oil) raises bad cholesterol (LDL) but also raises good cholesterol (HDL). One negative effect, one positive effect.

-Eating unsaturated fats – UFs – (MUFAs – monounsaturated fats – found in plant oils such as olive, canola, and peanut oil; PUFAs – polyunsaturated fats – found in plant oils such as safflower, sunflower, corn or soybean oil, fish with omega-3 fat) lowers the bad cholesterol (LDL) and lowers the good cholesterol (HDL). One positive effect, one negative effect.

-Eating industrially produced trans fats – TFs – (vegetables oils that have been chemically changed by a process called hydrogenation to make them solid at room temperature found in margarine, many fast foods, snack foods and fried or baked goods) is highly dangerous because it does two bad things – raises bad cholesterol (LDL) and lowers good cholesterol (HDL).

-Replacing saturated fats with carbohydrates (CHO) may actually increase cardiovascular risk unless carbohydrates come from whole-grain fibre-rich sources. Studies have shown that carbohydrates with high glycemic index –GI – (a measure of the effects of foods on blood-sugar levels) increase cardiovascular risk by 33 per cent.

Do you find all this confusing? You are not alone.

Next time you go to a grocery store, tell the helper (if you can find one) to give you some SFAs, PUFAs, MUFAs, no TFs, no LDL, lots of HDL, healthy CHOs and some low GI food. See what you get and surprise your family. Happy eating.

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