The Paleo Diet - Loren Cordain [65]
This leaves only two vegetable oils (canola and flaxseed) that do not contribute to an elevated intake of omega 6 fatty acids. A number of epidemiological (population) studies have shown a higher risk of developing prostate cancer with an increased consumption of alpha linolenic acid (ALA), a major fatty acid found in both canola and flaxseed oil. However, epidemiological studies are notorious for their conflicting results. For every six studies that support one nutritional concept, you can often find half a dozen more that conclude precisely the opposite. Such is the case linking ALA and flaxseed oil to an increased prostate cancer risk. A series of the most recent epidemiological studies was unable to statistically show that ALA consumption increased prostate cancer risk. More important, in experiments in which animals were fed flaxseed oil, the flaxseed actually inhibited the growth and development of prostate cancer. The case supporting flaxseed oil as a promoter of prostate cancer is currently based solely on epidemiological evidence and therefore remains inconclusive because of the total lack of confirming experimental evidence. Because the majority of epidemiological studies support the notion that ALA is protective against cardiovascular disease, flaxseed oil should still be viewed as healthful.
Since the original publication of The Paleo Diet in 2002, I have reversed my view of canola oil and can no longer support its consumption or use. Let me explain why. Canola oil comes from the seeds of the rape plant (Brassica rapa or Brassica campestris), which is a close relative of broccoli, cabbage, Brussels sprouts, and kale. Clearly, humans have eaten cabbage and its relatives since prior to historical times, and I still strongly support the consumption of these health-promoting vegetables. The concentrated oil from the seeds of Brassica plants is another story.
In its original form, rape plants produced a seed oil that contained high concentrations (20 to 50 percent) of erucic acid (a monounsaturated fatty acid labeled 22:1n9), which I have previously explained is toxic and which causes a wide variety of pathological changes in laboratory animals. In the early 1970s, plant breeders from Canada developed a strain of rape plant that produced a seed with less than 2 percent erucic acid (hence the name canola oil). The erucic acid content of commercially available canola oil averages 0.6 percent. Despite its low erucic acid content, however, a number of experiments in the 1970s showed that even at low concentrations (2.0 percent and 0.88 percent), canola oil fed to rats could still produce minor heart scarring that was considered “pathological.”
A series of recent rat studies of low-erucic canola oil conducted by Dr. Ohara and colleagues at the Hatano Research Institute in Japan reported kidney injuries, as well as increases in blood sodium levels and abnormal changes to a hormone, aldosterone, that regulates blood pressure. Other negative effects of canola oil consumption in animals at 10 percent of calories include decreased litter sizes, behavioral changes, and liver injury. A number of recent human studies of canola/rapeseed oil by Dr. Poiikonen and colleagues at the University of Tempere in Finland have shown it to be a potent allergen in adults and children and indicate that it may cause allergic cross-reactions from other environmental allergens in children with atopic dermatitis (skin rashes).
Based on these up-to-date studies in both humans and animals, I prefer to be on the safe side and can no longer recommend canola oil.
Both olive oil and avocado oil are high (73.9 and 70.6 percent, respectively) in cholesterol-lowering monounsaturated fatty acids but have less than favorable