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What are the Most Common Flax Side Effects?

Harriette Halepis
Harriette Halepis

Basic flax side effects include flatulence and stomach upset. When tested on animals, flaxseed can create various other side effects, though these effects have yet to be seen in humans. When consuming any kind of flax, including flaxseed, oil, and meal, it is best to ingest these substances in moderation.

Ingesting a large amount of uncooked flaxseed, ten tablespoons (148 mL) or more, may result in poisoning. Since flax contains cynogenic glycosides, consuming more than the recommended amount of flax can be toxic. Some nutritionists also believe that consuming a large amount of flax, in any form, may lead to hormonal imbalance.

Flax seeds.
Flax seeds.

Animal studies have shown that a large amount of flax may interfere with hormones. These studies have caused some concern, though scientists do not believe that humans are affected by the grain in the same manner than animals are. So far, any connection between flax and birth defects has not been proven.

Aside from stomach upset, almost all flax side effects occur when it has been consumed in large quantities. Regular consumption of flax may cause diarrhea and loose stools. While most nutritionists tout the benefits of flax, it is a wise idea to speak with a medical doctor before beginning any diet regimen that includes flax of any kind.

The flowers of a flax plant.
The flowers of a flax plant.

It is also important to consume flax that is fresh. Flax meal can become rancid if it is left on a store shelf for a long period of time. Thus, many people purchase whole flax seeds, and then grind the seeds in order to create flax meal. If rancid meal has been consumed, the side effects can include vomiting and nausea. Since the effects of flax on pregnant women is largely unknown, many health experts recommend that pregnant women avoid flax or consume it with caution.

Flaxseed oil should be ingested in moderation.
Flaxseed oil should be ingested in moderation.

Most health experts agree that flax has many nutritional benefits, including a high amount of dietary fiber, that should not be ignored. Any flax side effects felt by the average person are usually minimal. When consuming flax for the first time, a person may feel slightly bloated and gaseous, though this is a normal reaction to flax.

Flax can be added to a number of different foods or consumed whole. In addition, flaxseed is frequently given to livestock as a form of feed. If any unusual flax side effects occur, it is best to stop taking the product and consult a medical doctor right away.

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Discussion Comments


@chrysalis - I just happened to buy some flax seeds at my health food store and asked the same question! The thing is, once you grind the flax seeds, the meal should be used within 60 days.

You can store the flax seeds much longer, up to a year, but in a cool, dry, dark place. If you use organic flax seed oil, here's a simple guide to go by: if it tastes bitter, don't use it. It should have a mild and nutty flavor.


Lately all I read about are flax seed benefits. Nice to finally read about the negative effects of flax seed.

What I'd like to know is how long is "too long" when leaving flax seed meal on the shelf before it becomes rancid?

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      By: Elenathewise
      Flax seeds.
    • The flowers of a flax plant.
      By: Marina Lohrbach
      The flowers of a flax plant.
    • Flaxseed oil should be ingested in moderation.
      By: spline_x
      Flaxseed oil should be ingested in moderation.