Thursday, December 17, 2009

Paleo Diet Q & A - 17 December 2009

Dear Readers,

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,

A: Deanna,

Please refer to Dr. Cordain's article on rheumatoid arthritis entitled "Modulation of immune function by dietary lectins in rheumatoid arthritis."


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  2. The following is a question that was not addressed in the Paleo Diet for Athletes book: does the Paleo Diet permit me to re-heat food in a microwave oven or does the microwave change the chemical composition of the food, rendering the food nutritionless?

  3. Posted on behalf of Maelán:


    There are some studies showing less adverse effects of microwave cooking compared to conventional cooking when it comes to nutritional value of meat, specially with the use of low power. Microwave cooking showed equal or better retention of nutrients such as thiamin, riboflavin, pyridoxine and ascorbic acid. There’s also some evidence showing that microwave cooking produces less toxic compounds such as nitrosamines and Heterocyclic Amines (HCA) compared to other cooking methods. On the other hand, Advanced
    Glycation End Products (AGE) is a potential toxic compound which presence was related to high temperature, cooking time and moisture, and produced by microwave cooking.

    Here you have some other effects of cooking meat:

    Heat and meat processing exert several deleterious effects upon meat quality
    as explained below:

    1. Maillard reaction in which the amino acid groups react with aldehyde groups of reducing sugars or carbonyl from oxidized fats. This process makes lysine unavailable for the body.

    2. Cross-linkage reactions. One example is the formation of =CH-N= links which are resistant to enzymatic reactions in the gut.

    3. Damage to sulphur amino acid by oxidation or desulphydration.

    Processing time is another crucial factor when it comes to nutrient quality of food. For example, pork processed at 110º for 24 h lost 44% cysteine, 34% available lysine and up to 20% of other amino acids.

    It has been suggested that the lost in sulphur amino acids represents the most serious adverse effect of cooking.

    There’s evidence that hunter-gatherers used to simmer food, i.e., they cooked during long periods of time at low temperatures.

    The bottom line is that high temperature and long cooking periods could damage meat and reduce the amount and quality of nutrients.

    We recommend simmer meat avoiding high temperature and cooking times in order to preserve the maximum biological value of the food and at the same time avoid possible toxic compounds.

    I hope this helps.

  4. I read the article you suggested on dairy products a nd Rhumathoid Arthritis (RA).
    It points to the negative impact of Lectins (in grains) and protein in milk. However, I don't see anything on Goat's milk.
    I don't have RA but found I am intolerant to cows'milk (and cheese). I do seem to tolerate goat cheese. I also find I can eat raw milk cheese (from cows) and experience few if any side-effects>
    Please comment
    Thank you


The Paleo Diet Team invites you to leave comments or post questions to our blog. We receive a great amount of feedback, but we are not able to always answer personally. We read all comments, and we are very interested in hearing your thoughts, learning about your experiences, and understanding what questions you have. Note that we review all comments before publishing them on the blog. Comments posted that do not contain questions or comments related to paleo nutrition, or those that point to web sites that do not provide content that would be deemed helpful to our readers, will be rejected.

Thank you.
The Paleo Diet Team