Flaxseed

What is flaxseed?

Flaxseed comes from the flax plant, Linum usitatissimum. According to NCCIH, it has a long history of use, including as a laxative in ancient Greece. Ground flaxseed contains insoluble fiber, a gel-forming soluble fiber called mucilage, lignans and alpha-linolenic acid (ALA), a plant omega-3 fatty acid. Flaxseed oil, by contrast, contains the fat but not the fiber.

What the research says

For bowel regularity, the most relevant studies use ground flaxseed in food. In a 12-week randomized trial in Clinical Nutrition ESPEN, 77 constipated adults with type 2 diabetes ate cookies containing 10 g of flaxseed or psyllium twice a day, or placebo cookies. Both fibers improved constipation symptoms and stool consistency versus placebo, and flaxseed appeared somewhat better. The study was single-blinded and small.

A 2020 randomized trial in China gave 90 adults with functional constipation either 50 g a day of flaxseed flour or lactulose for four weeks. Both groups improved, and median bowel movements rose from two to seven a week with flaxseed. There was no placebo group.

Results in IBS are less clear. A small 2012 pilot trial found no statistically significant difference in IBS symptom severity between whole linseeds, ground linseeds and no linseeds after four weeks.

NCCIH summarizes the broader research as being of varying quality, with some interest in weight, blood sugar and the gut microbiome, but no firm conclusions.

How it’s used in supplements

Trials used 10 to 50 g a day, roughly one to five tablespoons of ground seed. A capsule blend that also contains nine other powders will deliver a tiny fraction of that. Ground flaxseed sprinkled on cereal or yogurt is the form with evidence for regularity.

On safety, NCCIH says limited amounts appear safe short term, higher doses can cause bloating, fullness and diarrhea, raw or unripe seeds should not be eaten, and there are theoretical concerns about interactions with blood thinners. Evidence on use during pregnancy is not conclusive.

Form matters with flaxseed. Whole seeds often pass through the gut undigested, so most studies used ground seed or flour. Ground flaxseed can go rancid, so it is best stored in the refrigerator. Flaxseed oil provides ALA but not the fiber and mucilage thought to help with regularity, so it is not a substitute for ground seed when the goal is bowel function.

A typical starting point is one tablespoon of ground flaxseed a day, mixed into oatmeal, yogurt or a smoothie, increasing gradually while drinking extra water. People who take blood thinners, diabetes medicines or hormone-sensitive medications should talk with their doctor before using larger amounts.