Are There Benefits to Soaking Flax Seeds Overnight?

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Like all legumes, nuts, and other seeds, flax does contain antinutrients, which reduce the bioavailability of its nutrients.

That’s why some people recommend soaking whole flax seeds for 8 hours (or overnight).

We’re going to quickly go over research on this topic to determine:

  • How big of a concern are antinutrients in flax?
  • Will soaking produce a benefit?
  • Should you eat whole vs ground flax seeds?

Antinutrients in Flaxseed

Research has shown that there are a few main types of antinutrients present in flaxseed that may be of concern (1). This includes:

  • Cyanogenic glycosides
  • Linatine
  • Trypsin inhibitor
  • Phytic acid

And before you get too scared about the presence of inorganic cyanide compounds, as long as you’re not eating some crazy amount of flax like 1 cup or more daily, it’s within the amount that humans can detoxify.

The main antinutrients that prevent absorption of vitamins and minerals are the trypsin inhibitor and phytic acid, which you may be familiar with already.

How Much Antinutrients Are in Flaxseeds?

The obvious next question is are these antinutrients a big deal?

That comes down to 2 factors: the amounts of them, and their actual impact.

It turns out that while flaxseed has a fairly high amount of antinutrients, they’re less active than in other foods. In other words, they’ll have less of an effect on nutrient absorption.

The table below shows the concentration of phytic acid in a variety of foods. Flax (aka linseed) actually has more phytic acid than even legumes (2):

phytic acid in flaxseed vs other foods

In addition, studies also show that flaxseed has a trypsin inhibitor content of approximately 2280 mg/100g to 3250 mg/100g, which is relatively high.

But all that doesn’t matter too much, because research has also shown that the activity of flaxseed antinutrients is quite low.

“Activity” refers to the actual impact on nutrient absorption.

Research has measured the trypsin inhibitor activity (TIA) of various foods and found (3):

  • Flaxseed meal: 14-37 units
  • Raw rapeseed meal: 99 units
  • Raw soybean meal: 1650 units

That really highlights why it’s a good idea to soak legumes.

SUMMARY

Flaxseed does have relatively high levels of both phytic acid and trypsin inhibitor, but the actual impact of those on nutrient absorption is quite low compared to other foods high in antinutrients.

Will Soaking Raw Flax Produce Benefits?

There’s a few more things I’d like to quickly point out for you to consider:

  1. Not all antinutrients are evil. Some research even suggests that some level of trypsin inhibitor is healthy (4).
  2. If you’re cooking your flax, a large portion of antinutrients will be destroyed, so soaking may be overkill.
  3. Soaking typically reduces phytic acid content by about 50%, so there will still be some left (5).

Soaking Whole vs Ground Flaxseed

If you’re concerned about nutrient absorption, another factor to consider is whether to eat flaxseed in ground or whole form.

In general, eating ground flaxseed is easier to digest, as the shell is nearly impossible for humans to break down if it hasn’t been chewed (i.e. opened) well.

On the other hand, soaking works by dissolving water-soluble antinutrients, which can then be washed away. This rules out soaking ground flaxseed.

Technically you could soak and sprout flax seeds, then dry them, and then grind them up, but this is an insane amount of work for most people.

Is It Worth It To Soak Flaxseed Overnight?

After all that, my personal conclusion would be that most people are better off eating ground flaxseed even if soaking is not involved.

The activity of the antinutrients is relatively low as we’ve seen, and flax has so many vitamins and minerals that it doesn’t really matter if a small portion isn’t absorbed.

If you’re really worried about antinutrients, cooking flax is another possible option, that typically reduces antinutrient content by about 80% (6).

References

  1. upm.edu
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4325021/
  3. https://link.springer.com/article/10.1007/BF02545351
  4. https://pubmed.ncbi.nlm.nih.gov/9505242/
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4325021/
  6. https://books.google.ca/books?id=SynoBwAAQBAJ&pg=PA156&redir_esc=y#v=onepage&q&f=false

About the author

Dale Cudmore

Your friendly neighborhood vegan from Toronto. I've spent over 6 years as a freelance nutrition writer and researcher. During this time, I've tested over 50 vegan protein powders, and over 100 other types of vegan supplements.

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