Dear Dr. Blonz: Are flaxseeds an appropriate source of omega-3 fats? I have been buying and sprinkling ground flaxseed on my cereal and also using it in baking. My concerns are a couple of conflicting bits of information that I found. One is that raw flaxseed is toxic until it is heated, and the other is that flaxseed oil is not toxic until it’s heated. What’s that all about? Is it OK to continue baking with ground flaxseed in muffins, bread, etc., instead of eating it raw? Or should I stick to unheated ground flaxseed, or simply use flaxseed oil? — F.S., Lodi, California

Dear F.S.: Lots of flax to go over here (sorry, couldn’t let that slip by). The fatty acids in flaxseed are highly unsaturated — more so than most other vegetable oils. The greater the degree of a fat’s unsaturation, the greater its susceptibility to oxidation because the unsaturated bond is a point of vulnerability. (Read more on fats at When food fats become oxidized, they lose their nutritive value and become rancid, which also messes with their taste, aroma and mouthfeel. Now, don’t overreact here, as this oxidation is not the same as becoming toxic, and a healthy body can handle this to a degree.

Exposure to the “oxidizing” rays of the sun, and to air, help make oxidation more likely, and heat also facilitates these reactions. All this explains why storing fats in sealed containers in a cool, dark place makes sense.

Now, we tie in the concept of the antioxidant, which is a substance that prevents oxidation by being more attractive to oxygen — sort of a biochemical “take me first” ethos. It also speaks to the unique value of extra virgin olive oil, with its own antioxidants, and to the healthfulness of a plant-based, whole-foods diet, which provides naturally occurring antioxidants to the body.

The flaxseed also has protectants, the primary being the protective seed coat that keeps the oil safe inside. The seed coat is so strong that most intact flaxseeds tend to pass right through our digestive systems. Inside the flaxseed are also several antioxidants — nature’s way of helping assure the viability of the seeds once planted. The healthful components of the flaxseed become available to us once the seeds are cracked or ground, but that process also increases the susceptibility to oxidation. This is why ground flaxseed should be stored in airtight containers and kept in the refrigerator once opened.

An issue relating to toxicity is the fact that flaxseed contains cyanogenic (cyanide-producing) compounds. Their mere presence does not make flaxseed dangerous; it all comes down to the amount of the compounds and the health of the consumer. Cyanogenic compounds are present in several other foods, and they cause problems primarily in malnourished individuals. The cyanogenic compounds in flaxseed are more a concern for livestock, where very large amounts are consumed. Heat can help in that situation because it breaks down the compounds into harmless substances.

As for purified flaxseed oil, that would provide you with the omega-3s of flax but not its naturally present fiber or phytochemicals. You would avoid the cyanogenic compounds — not much of a risk at the levels consumed — but the risk of rancidity would remain.

If you are interested in using flaxseed oil, look for a brand that contains all the beneficial compounds found in the intact seed, including the phytochemicals known as lignans. Flaxseed oils, particularly when purchased as liquids, should be stored in the refrigerator or freezer.

(Ed Blonz, Ph.D., is a nutrition scientist and an assistant clinical professor at the University of California, San Francisco. He is the author of the digital book “The Wellness Supermarket Buying Guide” (2012), which is also available as a free digital resource at