While flaxseed oil should not be heated because it can easily oxidize and lose too many of its valuable nutrients, it appears that heat does not have the same effect on whole flaxseeds. Flaxseeds contain a high concentration of alpha-linolenic acid (ALA). Our website profile shows them to contain over 3 grams of ALA in 2 tablespoons, and this amount of ALA represents 54% of their total fat content. Flaxseeds contain not only ALA, however, but other important nutrients as well, including vitamins, minerals, fiber, and lignan phytonutrients such as secoisolariciresinol diglucoside (SDG).
Research studies have shown that the ALA in flaxseeds and the lignan phytonutrients in this food are surprisingly heat stable. For this reason, we believe that it safe to use flaxseeds in baking and still receive substantial amounts of ALA and other nutrients when consuming the flax-containing cooked foods.
Studies testing the amount of omega-3 fat in baked goods indicate no significant breakdown or loss of beneficial fats occurs in baking. For example, in one study, the ALA content of muffins containing 25 grams of flaxseeds was not significantly reduced after baking. Researchers speculate that the omega-3 fats in flaxseed are resistant to heat because they are not isolated but rather are present in a matrix of other compounds that the flaxseeds contain, including the lignan phytonutrients that have antioxidant properties.
It's also worth pointing out that the temperatures used for baking were normal baking temperatures of 350°F (177°C) and higher—not specially lowered temperatures to see if the seeds needed lower heat to keep their ALA intact. Baking times were also normal—falling in the one to two hour range. In one study, the seeds were even exposed to a heat level of 660°F (349°C), apparently without damaging their ALA content.
The lignan phytonutrient SDG has also be found to be stable in its chemical structure when exposed to normal baking conditions. In one study, consumption of SDG-enriched muffins was found to enhance the production of mammalian lignans in women, reflecting their stability and bioavailability. In another study, women who ate raw, ground flaxseed daily for four weeks had similar plasma fatty acid profiles as those who ate milled flaxseed that had been baked in bread. Both groups of women showed a lowering of total cholesterol and "bad" LDL cholesterol, further reflecting that flaxseeds still have benefits when used in baked goods.
A study on incorporation of flaxseeds into pasta - involving overnight drying of the flax-containing pasta at temperatures of either 104F(40C) or 178F (80C) plus boiling of the dried pasta - also showed a reduction in ALA of 8% or less. And a study on the boiling of flax bolls (the seed-containing portion of the plant) showed a reduction in ALA of 4-5%. All of these studies are consistent in demonstrating the relatively stable nature of ALA in flaxseeds to heat.
Based upon these research studies (all cited in the References section below), it appears that the ALA in flaxseeds is relatively stable to heat, and that flaxseeds can provide substantial ALA benefits even after processing, incorporation into cooked foods.
Cunnane SC, Ganguli S, et al. High alpha-linolenic acid flaxseed (Linum usitatissimum): some nutritional properties in humans. Br J Nutr. 1993 Mar;69(2):443-53.
Cunnane SC, Hamadeh MJ, Liede AC, et al. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr. 1995 Jan;61(1):62-8.
Fofana B, Cloutier S, Kirby CW, et al. A well balanced omega-6/omega-3 ratio in developing flax bolls after heating and its implications for use as a fresh vegetable by humans. Food Research International, Volume 44, Issue 8, October 2011, Pages 2459-2464.
Hallund J, Ravn-Haren G, et al. A lignan complex isolated from flaxseed does not affect plasma lipid concentrations or antioxidant capacity in healthy postmenopausal women. J Nutr. 2006 Jan;136(1):112-6.
Hyvarinen HK, Pihlava JM, et al. Effect of processing and storage on the stability of flaxseed lignan added to bakery products. J Agric Food Chem. 2006 Jan 11;54(1):48-53.
Manthey FA, Lee RE, Hall CA 3rd. Processing and cooking effects on lipid content and stability of alpha-linolenic acid in spaghetti containing ground flaxseed. J Agric Food Chem. 2002 Mar 13;50(6):1668-71.
Villeneuve S, Des Marchais LP, Gauvreau V, et al. Effect of flaxseed processing on engineering properties and fatty acids profiles of pasta. Food and Bioproducts Processing, Volume 91, Issue 3, July 2013, Pages 183-191.