Maelán Fontes' Response:
Hi Tim,
We think your thoughts are on the right track.
When Dr. Cordain wrote The Paleo Diet book, the advice to consume flaxseed 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. Therefore, 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 situation, 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:
- Hunter-gatherers do not eat ALA from seeds or vegetable oils.
- Nuts, green leafy vegetables and animal foods contain ALA.
- The conversion of ALA to EPA+DHA is limited, due to low delta-6 and delta-5 activity, although ALA is highly oxidized (twice that of LA) (see paper by Freemantle et al). This means that at some point in 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.
- The essentiality of LA & ALA in human metabolism has been questioned (see paper by Le et al.), as we relied almost on LCPUFA (Arachidonic Acid, EPA and DHA) during the Palaeolithic 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.
- The possible toxicity from seeds and vegetable oils (HCN, saponins, lectins).
- 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.
- The well known positive health effects of fish oil supplementation (among other factors to improve omega-6/omega-3 ratio) in contrast with some possible adverse effects of flaxseed 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 flaxseed 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 oils).
Hope this helps,
Maelán Fontes Villalba - MS Ph.D. candidate in Medical Sciences at Lund University, Sweden
