Paleo Diet Q & A - 22 January 2010

Dear Readers,

Today's edition of Paleo Diet Q & A discussing flax seed and flax seed oil consumption.

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Q: Dear Dr. Cordain,

I recently visited family over the holidays and my brother is a new advocate of the Paleo Diet. For breakfast he made us "fakecakes" which had about 1-2 tablespoons of flax seed in them that he ground in a coffee grinder. I had few a questions regarding the use of flax seed in the Paleo Diet.

Firstly why are flax seeds ok in the Paleo Diet but other grains (seeds) are not? My understanding for eliminating grains from the diet is the toxins that they contain but flax seed contains large amounts of cyanogenic glycosides producing up to 139 mg/kg of hydrogen cyanide in raw human-grade flax seed. I am sure flax seeds are processed somehow before selling them but I don't know what process that is or what effect it has on the HCN concentration.

So, secondly...do you know of any studies on the amount of HCN in meals containing ground flax seed and the chronic oral exposure of those amounts on humans? My understanding here is the HCN that isn't hydrolysed to formic acid in the stomach and doesn't bind to hemoglobin is converted to thiocyanate which hinders thyroid function.

Thank you for your time and any information you can supply.

Sincerely,
Tim

A: Hi Tim,

We think your thoughts are on the right track.

When Dr. Cordain wrote The Paleo Diet, the advice to consume flax seed oil was an attempt to balance the increased omega-6/omega-3 fatty acid ratio due to the exaggerated intake of omega-6 vegetable oils, especially linoleic acid, in the typical western diet.

Nevertheless, animal foods (fish, muscle meat and organs from wild animals) are good sources of w3 fatty acids. As so, when people eat these foods regularly along with vegetables and nuts, and avoid vegetable oils (especially oils rich in Linoleic Acid – Omega 6), they get a balanced intake of omega 3, omega 6, monounsaturated and saturated fatty acids. In this context, there is no need for flax seeds to provide Omega 3 fatty acids and balance the Omega 3/Omega 6 ratio.

Here are some facts that support the notion that animal foods, vegetables and nuts provide the necessary Omega 6 and Omega 3 fatty acids in the right proportion:

1. Hunter-gatherers do not eat ALA from seeds or vegetable oils.
   
   
2. Nuts, green leafy vegetables and animal foods contain ALA.
   
   
3. The conversion of ALA to EPA+DHA is limited, due to low delta-6 and delta-5 activity, although ALA is highly oxidized (twice as much as LA) (Freemantle et al.). Therefore, this means that at some pointing history we included preformed sources of EPA and DHA and still need to do so. Animal foods (especially brain from wild ruminants and fish) are very good sources of these fatty acids.
   
   
4. The essentiality of LA & ALA in human metabolism has been questioned (Le et al.), as we relied almost on LCPUFA (Arachidonic Acid, EPA and DHA) during the Paleolithic era (see Dr. Cordain’s papers on that here and here). Moreover, there is already some evidence showing that human metabolism could re-convert AA and DHA into LA and ALA respectively, hence AA and DHA would be the true essential fatty acids.
   
   
5. The possible toxicity from seeds and vegetable oils (HCN, saponins, lectins).
   
   
6. They are not used by current HG societies, and these populations show no signs of western disease, so this means that flax seeds are not necessary.
   
   
7. The well known positive health effects of fish oil supplementation (among other factors to improve omega-6/omega-3 ratio) in contrasts with some possible adverse effects of flax seed oil (like the epidemiological evidence that points towards increased risk of prostate cancer with flax oil consumption – see paper by Brouwer et al).

The bottom line from an evolutionary perspective is that flax seeds and/or flax seed oil would not have been consumed by pre-agricultural humans. However, having said that, hunter gatherers always would have preferentially sought high oil plant foods as per optimal foraging theory. But, most high fat plant foods contain high MUFA (with the exception of coconut and palm).

In addition, we will continue to explore the broader impact to health of modern vegetable oils, including flax.

Hope this helps.
Maelán