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OMAD and protein / fiber / micronutrient intake

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Thanks Mccoy for the articles on soy.  (I’m familiar with the Messina article, and I posted an excerpt from  it previously:  https://www.crsociety.org/topic/14242-why-does-soy-reduce-estrogen-levels-in-studies/?tab=comments#comment-25421 )

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Mccoy:  Isoflavones are regarded as beneficial if intake is not excessive. The threshold is not well defined. One gallon soymilk per day has resulted in acute negative symptoms, whereas the equivalent of 15 grams of soy protein per day is regarded to be all right.

Of course intake which is “excessive” is by definition not beneficial, so determining a safety threshold  is critical.  However, based on the two cited articles, it seems that such a threshold isn’t just “not well defined”, it’s not defined at all. 

The Messina article is thorough and comprehensive.    The author concludes:

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Concerns that the estrogen-like properties of isoflavones produce untoward effects in some subpopulations, such as postmenopausal women, are not supported by the clinical and epidemiologic research. Evidence indicates soy foods can be safely consumed by all individuals except those who are allergic to soy protein, which is relatively uncommon in comparison to the number of individuals allergic to many other commonly-consumed foods

There doesn’t appear to be any mention of a specific threshold beyond which isoflavone intake becomes harmful.

The Rizzo and Baroni article, while slightly more cautious in its conclusions, also does not identify any specific isoflavone safety threshold

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Sex hormone network and thyroid gland perturbation seems to be unlikely, especially with low isoflavone intakes actually reported in vegetarian. Overall, the low content of bioactive compounds in second generation soy foods and moderate amounts in traditional soy preparations offer modest health benefits with very limited risk for potential adverse health effects [570]. At the same time, to have the beneficial effects of soy isoflavones, intake should be at least of 60–100 mg per day [571], at present not easily reached in Western countries.

 

Regarding the passage you highlighted: 

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Daily administration of 54 mg of genistein in aglycone form to menopausal women for 3 years did not affect thyroid function [406]. Moreover, 200 mg of isoflavones daily administration for 2 years did not influence TSH [501]. Isoflavones showed an overall good profile of safety for thyroid function [413].

In 2015 an EFSA panel concluded that the intake of 35–150 mg per day of isoflavones from supplements or foods does not have adverse effect on sex hormones-responsive tissues such as breast and uterus or thyroidal gland up to 2.5 years duration of intake [502].

You  calculate that 54 mg of genistein represents approximately 15 grams of soy protein (based on Messina’s 3.5 g isoflavone per gram of soy protein formula),  but according to Messina:

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The three isoflavones genistein, daidzein and glycitein and their respective glycosides account for approximately 50%, 40% and 10%, respectively, of the total isoflavone content of soybeans [68].

Since genistein and its glycosides make up only around  half of soybean isoflavone content, wouldn't it take approximately 30 grams of protein or more, not 15, to yield 54mg of genistein?

Another minor point:   the 54 grams of genistein were administered in an unnatural purified, isolated aglycone form which some argue is more quickly and better absorbed (there is conflicting evidence in that regard), avoids interference effects and may be less biologically active compared to the natural glucoside isoflavone forms found in soy products.  (See references below.)

The critical point, though, is that the 54 grams of purified aglycone genistein had no negative health effects .  Neither did 200mg of isoflavones the other cited study.  There is no suggestion that an amount of soy protein yielding similar isoflavone content represents an upper limit beyond which negative health effects can be expected, especially outside special population subgroups.

Of course,  I’m not suggesting drinking soy milk by the gallon.  I don’t advocate  a very high intake of polyphenols from any particular source,  whether from  olives, grapes, green tea, citrus fruits or whatever.

On the other hand,  the  literature suggests that soy intake is remarkably safe,  and, as far as I can tell, there  is no scientific basis for a soy protein safety threshold anywhere near something as low as 15 grams.

 

Bioavailability of phyto-oestrogens.

Rowland I  et al.

Br J Nutr. 2003 Jun;89 Suppl 1:S45-58.I

https://www.ncbi.nlm.nih.gov/pubmed/12725656

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Isoflavones are present predominantly as glucosides in most commercially available soya products; there is evidence that they are not absorbed in this form and that their bioavailability requires initial hydrolysis of the sugar moiety by intestinal beta-glucosidases. After absorption, phyto-oestrogens are reconjugated predominantly to glucuronic acid and to a lesser degree to sulphuric acid. Only a small portion of the free aglycone has been detected in blood, demonstrating that the rate of conjugation is high.

 

 Isoflavones: estrogenic activity, biological effect and bioavailability.

Vitale DC1, et al.

Eur J Drug Metab Pharmacokinet. 2013 Mar;38(1):15-25

https://www.ncbi.nlm.nih.gov/pubmed/23161396

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Numerous clinical studies claim benefits of genistein and daidzein in chemoprevention of breast and prostate cancer, cardiovascular disease and osteoporosis as well as in relieving postmenopausal symptoms. The ability of isoflavones to prevent cancer and other chronic diseases largely depends on pharmacokinetic properties of these compounds, in particular absorption and distribution to the target tissue. The chemical form in which isoflavones occur is important because it influences their bioavailability and, therefore, their biological activity.

Glucose-conjugated isoflavones are highly polar, water-soluble compounds. They are hardly absorbed by the intestinal epithelium and have weaker biological activities than the corresponding aglycone. Different microbial families of colon can transform glycosylated isoflavones into aglycones. Clinical studies show important differences between the aglycone and conjugated forms of genistein and daidzein.

 

Update on genistein and thyroid: an overall message of safety

Herbert Marini

Front Endocrinol (Lausanne). 2012; 3: 94.

10.3389/fendo.2012.00094

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Recently, clinical trials have been conducted to evaluate the benefit of genistein aglycone as a cure for menopausal vasomotor symptoms, osteoporosis, and cardiovascular disease. Specifically, administration of 54 mg/day genistein aglycone to postmenopausal women with low bone mass results in positive (beneficial) changes in vasomotor symptoms, bone mineral density and markers of bone turnover, and some predictors of cardiovascular risk without harmful estrogenic activity in the breast and uterus (Atteritano et al., 2007; Marini et al., 2007, 2008, 2010; D’Anna et al., 2009). In those studies, administration of pure genistein avoided possible interferences by other isoflavones and resulted in documented and stable increases of the isoflavone’s serum level.

Edited by Sibiriak

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On 7/10/2019 at 1:28 PM, Sibiriak said:

n 2015 an EFSA panel concluded that the intake of 35–150 mg per day of isoflavones

Sibiriak, you're right on genistein on its own, but the above cited would represent a pretty wide interval of total isoflavones whose lower bound would correspond to 10 g soy protein so 15 g would be a reasonable cautious amount. But that's a specific study on women.

I've not been able to track the source(s) I read for that generic figure, not even in Jack Norris webpage on soy, part 2

https://veganhealth.org/soy-part-2/

What is useful though is a ballpark figure, I myself have been eating often (much) more than 15 grams of soy protein. Also it seems that soy protein isolate has not so much isoflavones as natural foods do.

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Maybe this is the source I remembered, a previous article by Messina & Messina, 2003

 

 
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Nutr Today. 2003 May-Jun;38(3):100-109.

Provisional Recommended Soy Protein and Isoflavone Intakes for Healthy Adults: Rationale.

Abstract

Health professionals and consumers are seeking guidance regarding appropriate soy intake levels. Several different types of evidence that support of our recommendation that adults should consume 15 g (range 10-25 g) soy protein and 50 mg isoflavones (range 30-100 mg)/day are presented.

PMID:
 
12813189

 

 
Edited by mccoy

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