The effect of soy constituents on thyroid function

[diogenes]

New paper in Frontiers in Thyroid Endocrinology showing that at least for 3 months, soy constituents have effects on thyroid function.

ORIGINAL RESEARCH ARTICLE

Front. Endocrinol., 22 November 2018 | doi.org/10.3389/fendo.2018....

The Effect of High Dose Isoflavone Supplementation on Serum Reverse T3 in Euthyroid Men With Type 2 Diabetes and Post-menopausal Women

Thozhukat Sathyapalan, Josef Köhrle, Eddy Rijntjes, Alan S. Rigby, Soha R. Dargham, Eric Kilpatrick and Stephen L. Atkin

1Academic Diabetes, Endocrinology and Metabolism, Hull York Medical School, University of Hull, Hull, United Kingdom

2Institut für Experimentelle Endokrinologie, Charité-Universitätsmedizin Berlin, Berlin Institute of Health, CVK, Humboldt-Universität zu Berlin, Berlin, Germany

3Weill Cornell Medical College Qatar, Doha, Qatar

4Department of Clinical Chemistry, Sidra Medical and Research Center, Doha, Qatar

Background: The health benefits of soy are widely reported but there are queries on the effect of soy isoflavones on thyroid function and the underlying mechanism of action.

Materials and Methods: We examined the effect of soy isoflavones on reverse tri-iodothyronine (or 3,3′,5′-tri-iodothyronine; rT3) in two studies comprising 400 patients: 200 men (study 1; 3 months) and 200 post-menopausal women (study 2; 6 months) who were randomized to consume 15 g soy protein with 66 mg of isoflavones (SPI) daily, or 15 g soy protein alone without isoflavones (SP) daily.

Results: SPI supplementation increased rT3 serum concentration in both men 0.41 (0.12) vs. 0.45 (0.14) nmol/L and women 0.33 (0.12) vs. 0.37 (0.09) nmol/L at 3 months compared to SP that was not seen at 6 months. Thyroid stimulating hormone (TSH) serum concentrations increased while free thyroxine (fT4) concentrations decreased with 3 months of SPI compared to SP supplementation for both men and women. rT3 correlated with TSH in both studies (p = 0.03) but not with either fT3 or fT4. fT3 levels did not differ between the SPI and SP preparations.

Conclusion: Soy isoflavones transiently increased rT3 levels within 3 months though reverted to baseline at 6 months. The mechanism for this would be either rT3 degrading deiodinase 1 and/or deiodinase 2 activities are transiently inhibited at 3 months, or inhibition of deiodinase 3, which generates rT3 from T4 is induced at 6 months. These changes were mirrored in the TSH concentrations, suggesting that short-term high dose isoflavone transiently impairs thyroid function in the first 3 months and may impact on general health during this period.

[Kitten44]

Ouch! In my not-too-long ago bodybuilding-gym-mad days I lived on SPI... plus peanut butter, tuna and broccoli! :-S

[jib70]

So not only is soya production razing forests in Argentina, Brazil and the Amazon it is not the wonder food we thought.

I understand it is also being used in animal feed (is it a cheap substitute?)

Maybe off topic here, but I just despair of the way this planet is being used for commercialism not for our benefit either.

[spongecat in reply to jib70]

I agree. It's going to get worse....much worse.

Soy products are everywhere and with the increase in veganism and vegetarianism who consume it probably more than those who partake in meat and dairy, we could be staring into a very deep rabbit hole in human health.

But of course it is pushed on us as a "wonder food". The isoflavines....I guess we will have to see how this all pans out.

[jib70 in reply to spongecat]

I'm a vegetarian who has found food containing soy seriously upset my digestion, yet at one time I believed it was a good source of protein.

As it is also used heavily in feeds for meat/dairy production it surely must be being absorbed by non veg/vegans also.

How to avoid it - mass production of food be it meat, dairy, veggie - means must be being absorbed insiduously whatever our diet?

Has this increased thyroid problems in the general population? Who knows.

[TSH110 in reply to jib70]

I totally agree. Plus a lot is genetically modified or contaminated with GM. Despite being told it is no different to natural breeding for desirable traits it strikes me it is anything but and it’s consequences are yet to be ascertained.

[TSH110 in reply to spongecat]

I should imagine meat eating is the main driver of its use not vegetarianism/veganism as it is fed to livestock on a massive scale most of the harvest is for animal feed according to R4 farming today. Only a relatively small proportion of the population are veggies or vegans too.

[greygoose in reply to jib70]

I've been saying for a long time that soy is not even food - let alone a super-food. It also contains antinutrients, so that you can't absorb the protein, etc. But, I just get shouted down by all those that think it's wonderful. I think it probably has had an effect on thyroids. It is, after all, a goitrogen. You can't buy a loaf of bread in the UK that doesn't contain soy flour.

[penny]

I don’t like the stuff and try and avoid it as much as possible, although with it’s inclusion in so many things that is difficult. I don’t buy ready-made food, thank goodness. We’re a farming family so won’t be going vegan.