Flaxseeds

What it is and how to eat it

The Dictionary of the Spanish Language defines linaza (flaxseed) as the seed of flax (Linum usitatissimum), in the form of hard, shiny, gray elliptical grains, and EFSA notes that flax has been grown for more than 8,000 years in Europe and Asia for its fiber and oil. It is sold whole or ground, and this page covers flaxseed according to USDA, with 534 kcal, 27.3 g of fiber, 18.3 g of protein, 42.2 g of fat and 22.8 g of alpha-linolenic acid (ALA), the plant omega-3, per 100 g.

A tablespoon of whole seeds weighs about 10 g according to USDA, and 10 g (0.4 oz) provides 53 kcal, 2.7 g of fiber, 1.8 g of protein and 2.3 g of ALA, so it adds fiber and omega-3 but does not replace the protein part of the plate. The 2025 nutrition advisory on GLP-1 therapy suggests avoiding fatty or high-fiber foods in the first days of treatment and, for constipation, increasing fiber gradually with enough fluids, so in those days a teaspoon over Greek yogurt or in oatmeal may be enough. In a trial with 30 g a day baked into muffins, ground flaxseed raised blood ALA after one month and whole flaxseed did not, and no one left the ground-seed group, while some left the whole-seed and oil groups because of digestive discomfort (Journal of the American College of Nutrition, 2008).

What the evidence says

With USDA's figures, 10 g of seeds provides 2.28 g of ALA, a worked example rather than a suggested amount, above the 2 g a day with which, according to the EU, the effect of the authorized claim "ALA contributes to the maintenance of normal blood cholesterol levels" is obtained (Regulations (EC) No 1924/2006 and (EU) No 432/2012); by contrast, the EU register lists as non-authorized the claims that credited flax or its oil with improving mood, flaxseed oil with supporting heart health and lignans, hormonally active compounds in flaxseed according to EFSA, with easing menopausal discomfort. Flaxseed contains cyanogenic glycosides, which release cyanide when it is ground or chewed: in its worst-case scenario, with the most contaminated sample (407 mg of cyanide per kg, against an average of 192.1 mg/kg), EFSA calculated in 2019 that an adult of average weight (73.9 kg) would reach the acute reference dose with 10.9 g of ground flaxseed at one time, only slightly more than the 10 g in the example above, and noted that whole, unground seeds would lead to much lower exposure. The EU caps hydrocyanic acid in flaxseed sold to consumers at 150 mg/kg, except when sold in small quantities with the warning "Only to be used for cooking and baking. Do not consume raw!" (Regulation (EU) 2023/915).

The sources for this section are listed under "Sources" at the end of the page.