Does eating flaxseed help your gut?

Flaxseed contains two types of active components for the gut: fibre and lignans. Both serve as food for gut bacteria. Laboratory models and animal studies have shown that flaxseed stimulates the production of short-chain fatty acids, including butyrate. Butyrate is an important fuel for the cells lining the gut wall and has a beneficial effect on its integrity.

The lignans in flaxseed, in particular a compound called secoisolariciresinol, are converted by gut bacteria into two other compounds: enterodiol and enterolactone. This process is well documented in laboratory and animal research. There is an interesting interplay involved in this conversion: you need healthy gut bacteria to activate the lignans, and the lignans in turn feed those bacteria.

The effect on the composition of the gut microbiome is mixed. In a laboratory model, overall bacterial diversity actually decreased, while in rat studies beneficial bacterial strains increased. How this plays out in humans over the long term has not yet been sufficiently studied. So far there is little direct clinical evidence from well-designed studies in humans that look specifically at gut health as an outcome.

What is well supported in humans are the cardiometabolic effects. At a dose of at least 30 grams of ground flaxseed per day, for at least twelve weeks, blood pressure, blood lipids and inflammatory markers decreased measurably. Part of this effect runs through the gut microbiome, which means it also indirectly says something about the gut mechanisms. That provides a concrete takeaway: ground flaxseed works better than whole seeds, because the fibre and lignans are then released more easily.