Thursday, December 17, 2009
Paleo Diet Q & A - 17 December 2009
Today's edition of Paleo Diet Q & A.
Q: I can’t seem to find a scientific answer with research to support why you do not recommend saturated fat and dairy in the diet. Can you please explain the mechanism by which saturated fat clogs arteries? And can you explain why you do not recommend dairy with biochemical explanations?
A: Saturated fatty acid intake and the risk of developing cardiovascular disease (CVD) is a topic with a lot of controversy. In recent years a wide body of research has suggested that increased consumption of certain saturated fatty acids (Lauric acid, myristic acid and palmitic acid) down-regulate LDL receptor and thereby increase LDL plasma levels, which has been associated to increased risk of CVD. On the other hand, stearic acid (a 18 carbon saturated fatty acid) has been shown to decrease LDL plasma levels. However, this view is too simplistic as there are several other factors contributing to CVD, such as smoking, exercise, trans-fatty acids, increased omega-6/omega-3 ratio, free-radicals, nutrient deficiency, homocysteine, alcohol intake and low-grade chronic inflammation among others.
Moreover, some studies have suggested that there’s not enough scientific data to support the view that increased total or LDL cholesterol is an independent risk factor for CVD, but rather oxidized LDL. Plaque production is mediated by oxidized LDL, not LDL. Oxidized LDL can produce shedding of the inner layer of the artery namely glycocalix. Oxidized LDL then infiltrates the intima of the artery. Oxidized LDL is eaten by macrophages, a process known as phagocytosis, causing macrophages to be transformed into foam cells which produce the fibrous cap.
Once the fibrous cap has been produced we need to break it down in order to produce an ischemic event. Lectins and low-grade chronic inflammation are involved in the activation of matrix metalloproteinases which break down the fibrous cap.
In summary, high total cholesterol or LDL levels do not increase CVD risk--rather oxidized LDL increases risk of CVD. To produce oxidized LDL requires the factors mentioned above. Hence, consumption of saturated fatty acids is not an issue if we control several other factors such as those mentioned.
Dr. Cordain wrote a book chapter and published a paper (with our team member Pedro Bastos) where he shows that saturated fat consumption in ancient hunter-gatherer populations were usually 10-15% above the recommended 10% of energy from saturated fats, yet they were non-atherogenic.
The bottom line is that we do not recommend cutting down saturated fatty acid intake, but decreasing high-glycemic load foods, vegetable oils, refined sugars, grains, legumes and dairy.
Regarding why we do not recommend dairy products: please refer to the following papers (12 MB zip file) supporting this recommendation.
Other recommended reading is Dr. Cordain and Pedro Bastos' last paper entitled "Dietary fat quality and coronary heart disease prevention: a unified theory based on evolutionary, historical, global and modern perspectives."
Q: I have read your book and gotten on your blog just today. What I would love help with is any information on rheumatoid arthritis which I could email on to a 70 year old female friend who is suffering terribly. I couldn't find a specific article I could forward on to her.
Thanks for any help you can give,
Please refer to Dr. Cordain's article on rheumatoid arthritis entitled "Modulation of immune function by dietary lectins in rheumatoid arthritis."