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RE: [RC] flax seed question/thyroid? - Susan E. Garlinghouse, DVM


>Hi all, I'm hoping Susan G. or Heidi or any other person that might have an answer to this question.
>I used to think flax seed was good in most cases, but something I read this weeked disturbed me.
>Had to do with the fact that flax had the potential of thyroid inhibition.
>Is this possibly true?  For humans and or horses? 
>I'm holding off on flax until I'm satisfied it is still okay to give.   I would appreciate some reassurance as I know it is widely feed to horses as well as human.
Flax is a minor source of some goitrogenic compounds, which potentially might be an issue in hypothyroid humans---on that point, I really don’t know, as humans are a pretty boring species that in any case, I’m not licensed to treat medically, and thus tend to ignore.<g>   However, almost any polyunsaturated oil is also a source of the same goitrogens, including soy, canola, corn oil, etc.  So I tend to be a bit skeptical that it’s much of an issue in humans if consumed at a fairly reasonable level, but don’t have any specific information on that point for you.

In horses, hypothyroidism tends to be pretty wildly overdiagnosed and overtreated---I’m not saying it doesn’t exist, but for most horses, thyroid inhibition just isn’t a major issue, except in horses that have clearly defined metabolic syndrome issues.  Flax does contain some goitrogenic compounds, as well as cyanogenic glycosides, much more so in the plant, leaves and immature seeds than in the mature seeds typically fed.  In the amounts typically fed to horses, it’s highly unlikely goitrogenic compounds would be an issue to even the slightest extent in ‘normal’ horses.  I know of several horses competing at international levels that go through better than 5 pounds a day, and there ain’t nuthin wrong with those horses at any level. 

As for the cyanogenic compounds, those are potentially an issue for ruminants that possess the digestive enzymes that break down the compounds into harmful components.  Cows and sheep have those enzymes in sufficient numbers to potentially cause a problem if they consumed a pretty vast amount of flax or linseed cake, but horses don’t.  Horses have these enzymes only in very low concentrations, insufficient to degrade the cyanogenic compounds to any significant extent, so again, it’s a non-issue, IMO.  Aside from all of that, selective cultivation of flax has reduced the cyanogenic content to virtually trace amounts, only---as a bit of trivia, raw soy is actually sky-high in the stuff, but it’s inactivated by cooking or fermentation.

If any of this worries you, though, you might also consider chia seeds as a source of omega-3s.  I haven’t finished up my reading into it (a very accomplished endurance rider friend just sent me something not too long ago), but it seems to be very promising as an equine supplement and has been happily fed to humans for a long time.

>Also, are there any suggestions to diet modification if any for a horse that may be "pre-cushings?"

Pre-cushings in what way?  Laminitis, cresty neck, that sort of thing?

Susan Garlinghouse, DVM



[RC] flax seed question/thyroid?, Kathie Ford