Best soy protein?

[argonzark]

What is the best soy protein isolate brand? I'm looking for one with eliminated or reduced anti-nutrients and added methionine.

And what does "tissue specific" mean?

[jechoa]

I dont know the best soy protein..but I do know soy counteracts with your thyroid and usually causes it to slow down....if you already have a thyroid problem...it will definately cause a bad reaction....if not it may take a while but it does affect it tremendously ..speaking from experience..be careful and read up on it...punch in thyroid and soy...and see what you get on the internet.

[argonzark]

Thanks for the tip. I dont have any thyroid problems, I think.. I don't even know what a thyroid is (:

I will check it out.

Any more comments?

[satanfuneral]

What is the best soy protein isolate brand? I'm looking for one with eliminated or reduced anti-nutrients and added methionine.

And what does "tissue specific" mean?

If u care about your testosterone levels & muscle gain, Never take soy protein.

[ravadongon]

Thanks for the tip. I dont have any thyroid problems, I think.. I don't even know what a thyroid is (:

I will check it out.

Any more comments?

Thyroid = thyroid gland = endocrine gland, produces various kinds of hormones.

BTW, I agree with what satanfuneral said.

[PowerSwede]

If u care about your testosterone levels & muscle gain, Never take soy protein.

I disagree, there have been studies that show no hormonal effects in males from intake of soy protein (1, 2, 3, 4) and another study showed that intake of soy protein LOWERED the amount of estrogen in males (1) and posesses anti-estrogenic effects (5, 6, 7, 8, 9, 10).

Soy protein can also increase the release of IGF-1 (11, 12, 13) and decrease bodyfat (14-36).

There are a lot more studies that show anti-estrogenic, anti-aromatase, decreased bodyfat, increased levels of IGF-1, decreased catabolism and increased protein synthetis (when compared to whey and/or caseine).

I got a collection of 127 studies that show the benefits of soy protein supplementation.

1. Nagata C, Inaba S, Kawakami N, Kakizoe T, Shimizu H. Inverse association of soy product intake with serum androgen and estrogen concentrations in Japanese men. Nutr Cancer. 2000;36(1):14-18.

2. Nagata C, Takatsuka N, Shimizu H, Hayashi H, Akamatsu T, Murase K. Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men. Cancer Epidemiol Biomarkers Prev. Mar 2001;10(3):179-184.

3. Mitchell JH, Cawood E, Kinniburgh D, Provan A, Collins AR, Irvine DS. Effect of a phytoestrogen food supplement on reproductive health in normal males. Clin Sci (Lond). Jun 2001;100(6):613-618.

4. Habito RC, Montalto J, Leslie E, Ball MJ. Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males. Br J Nutr. Oct 2000;84(4):557-563.

5. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. Apr 1997;29(2):95-120.

6. Cassidy A. Potential tissue selectivity of dietary phytoestrogens and estrogens. Curr Opin Lipidol. Feb 1999;10(1):47-52.

7. Kurzer MS. Hormonal effects of soy isoflavones: studies in premenopausal and postmenopausal women. J Nutr. Mar 2000;130(3):660S-661S.

8. Castle EP, Thrasher JB. The role of soy phytoestrogens in prostate cancer. Urol Clin North Am. Feb 2002;29(1):71-81, viii-ix.

9. Gaynor ML. Isoflavones and the prevention and treatment of prostate disease: is there a role? Cleve Clin J Med. Mar 2003;70(3):203-204, 206, 208-209 passim.

10. Messina MJ. Emerging evidence on the role of soy in reducing prostate cancer risk. Nutr Rev. Apr 2003;61(4):117-131.

11. Wangen KE, Duncan AM, Merz-Demlow BE, et al. Effects of soy isoflavones on markers of bone turnover in premenopausal and postmenopausal women. J Clin Endocrinol Metab. Sep 2000;85(9):3043-3048.

12. Romagnoli E, Minisola S, Carnevale V, et al. Effect of estrogen deficiency on IGF-I plasma levels: relationship with bone mineral density in perimenopausal women. Calcif Tissue Int. Jul 1993;53(1):1-6.

13. Khalil DA, Lucas EA, Juma S, Smith BJ, Payton ME, Arjmandi BH. Soy protein supplementation increases serum insulin-like growth factor-I in young and old men but does not affect markers of bone metabolism. J Nutr. Sep

14. Aoyama T, Fukui K, Nakamori T, et al. Effect of soy and milk whey protein isolates and their hydrolysates on weight reduction in genetically obese mice. Biosci Biotechnol Biochem. Dec 2000a;64(12):2594-2600.

15. Aoyama T, Fukui K, Takamatsu K, Hashimoto Y, Yamamoto T. Soy protein isolate and its hydrolysate reduce body fat of dietary obese rats and genetically obese mice (yellow KK). Nutrition. May 2000b;16(5):349-354.

16. Volgarev MN, al. e. Evaluation of isolated soy protein foods in weight reduction with obese hypercholesterolemic and normocholesterolemic obeste individuals. Nutr Rep Int. 1989;39(61).

17. Goodman-Gruen D, Kritz-Silverstein D. Usual dietary isoflavone intake is associated with cardiovascular disease risk factors in postmenopausal women. J Nutr. Apr 2001;131(4):1202-1206.

18. Ishihara K, al: e. Effect of soybean peptide on suppression of body fat accumulation uring endurance swimming in mice. Nutr Sci Soy Protein. 1996;17:94-97.

19. Kagawa K, Matsutaka H, Fukuhama C, Fujino H, Okuda H. Suppressive effect of globin digest on postprandial hyperlipidemia in male volunteers. J Nutr. Jan 1998;128(1):56-60.

20. Kawano-Takahashi Y, Ohminami H, Okuda H, et al. Effect of soya saponins on gold thioglucose (GTG)-induced obesity in mice. Int J Obes. 1986;10(4):293-302.

21. Bosello O, Cominacini L, Zocca I, et al. Short- and long-term effects of hypocaloric diets containing proteins of different sources on plasma lipids and apoproteins of obese subjects. Ann Nutr Metab. 1988;32(4):206-214.

22. Jenkins DJ, Wolever TM, Spiller G, et al. Hypocholesterolemic effect of vegetable protein in a hypocaloric diet. Atherosclerosis. Aug 1989;78(2-3):99-107.

23. Yama****a T, Sasahara T, Pomeroy SE, Collier G, Nestel PJ. Arterial compliance, blood pressure, plasma leptin, and plasma lipids in women are improved with weight reduction equally with a meat-based diet and a plant-based diet. Metabolism. Nov 1998;47(11):1308-1314.

24. Goodman-Gruen D, Kritz-Silverstein D. Usual dietary isoflavone intake and body composition in postmenopausal women. Menopause. Sep-Oct 2003;10(5):427-432.

25. Evans EM, van Pelt RE, Racette SB, Villareal DT, Holloszy JO. Soy protein enhances body composition in postmenopausal women. FASEB J. 2004;18(5):A873.

26. Szkudelska K, Nogowski L, Szkudelski T. Genistein affects lipogenesis and lipolysis in isolated rat adipocytes. J Steroid Biochem Mol Biol. Dec 31 2000;75(4-5):265-271.

27. Szkudelska K, Szkudelski T, Nogowski L. Daidzein, coumestrol and zearalenone affect lipogenesis and lipolysis in rat adipocytes. Phytomedicine. May 2002;9(4):338-345.

28. Iritani N, Hosomi H, Fukuda H, Tada K, Ikeda H. Soybean protein suppresses hepatic lipogenic enzyme gene expression in Wistar fatty rats. J Nutr. Feb 1996;126(2):380-388.

29. Nogowski L, Mackowiak P, Kandulska K, Szkudelski T, Nowak KW. Genistein-induced changes in lipid metabolism of ovariectomized rats. Ann Nutr Metab. 1998;42(6):360-366.

30. Frayn KN. Metabolic Regulation. 1st ed ed: Portland Press; 1996.

31. Vernon RG, Barber MC, Travers MT. Present and future studies on lipogenesis in animals and human subjects. Proc Nutr Soc. Aug 1999;58(3):541-549.

32. Hellerstein MK. De novo lipogenesis in humans: metabolic and regulatory aspects. Eur J Clin Nutr. Apr 1999;53 Suppl 1:S53-65.

33. Persky VW, Turyk ME, Wang L, et al. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr. Jan 2002;75(1):145-153.

34. Forsythe WA, 3rd. Soy protein, thyroid regulation and cholesterol metabolism. J Nutr. Mar 1995;125(3 Suppl):619S-623S.

35. Barth CA, Scholz-Ahrens KE, de Vrese M, Hotze A. Difference of plasma amino acids following casein or soy protein intake: significance for differences of serum lipid concentrations. J Nutr Sci Vitaminol (Tokyo). Oct 1990;36 Suppl 2:S111-117.

36. Sanchez A, Hubbard RW. Plasma amino acids and the insulin/glucagon ratio as an explanation for the dietary protein modulation of atherosclerosis. Med Hypotheses. Aug 1991;35(4):324-329.

[strongarm123]

Good soy protein? Oxymoron.

[PowerSwede]

I dont know the best soy protein..but I do know soy counteracts with your thyroid and usually causes it to slow down....if you already have a thyroid problem...it will definately cause a bad reaction....if not it may take a while but it does affect it tremendously ..speaking from experience..be careful and read up on it...punch in thyroid and soy...and see what you get on the internet.

No it does not, it raises both T3 and T4 levels (1, 2, 3), something that most people want since it helps you burn fat.

1. Persky VW, Turyk ME, Wang L, et al. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr. Jan 2002;75(1):145-153.

2. Forsythe WA, 3rd. Soy protein, thyroid regulation and cholesterol metabolism. J Nutr. Mar 1995;125(3 Suppl):619S-623S.

3. Barth CA, Scholz-Ahrens KE, de Vrese M, Hotze A. Difference of plasma amino acids following casein or soy protein intake: significance for differences of serum lipid concentrations. J Nutr Sci Vitaminol (Tokyo). Oct 1990;36 Suppl 2:S111-117.

[mattman]

i've been using a couple ounces of soy milk in my protein shakes, haven't noticed it do anything bad to me?

[K_muscle]

Good soy protein? Oxymoron.
lol true

[argonzark]

Unlike PowerSwede, soy protein detractors have very little science to back their opinions with.

I have also researched a bit on the topic and I found nothing wrong with soy protein, especially isolates. It looks to me like it got a bad rep because of some questionable studies and word of mouth, and then it somehow stuck. Of course everytime you bring such side effects as lowered testosterone or testicle shrinkage guys are gonna freak out and do away with reason haha :D

But, so far, no answers to my questions... :confused:

[milkl0ver2]

tofu.

[whiplash]

tofu.

I was about to say the same thing.

Most asian foods are rich in soy protein and soy related products.

chick peas, kidney beans.

[argonzark]

I'm asking about soy protein isolate brands, aka powders & supplements. :confused:

[milkl0ver2]

just buy some tofu and eat it with soysauce. tastes so much better.

[argonzark]

I don't care about taste, I need something in powder-form to put in a protein shake. I eat tofu sometimes but that is not related my question.

[cody3308]

Damn Im confused now, I told 2 people today that more than 25g of soy is bad for guys, I think Loki or Alan should post their thoughts to help destroy the myths :)

Also argon is there a reason it needs to be soy? could it be casien? cause then you could get the greatest tasting supp. of all ...MUSCLE MILK

[satanfuneral]

I disagree, there have been studies that show no hormonal effects in males from intake of soy protein (1, 2, 3, 4) and another study showed that intake of soy protein LOWERED the amount of estrogen in males (1) and posesses anti-estrogenic effects (5, 6, 7, 8, 9, 10).

Soy protein can also increase the release of IGF-1 (11, 12, 13) and decrease bodyfat (14-36).

There are a lot more studies that show anti-estrogenic, anti-aromatase, decreased bodyfat, increased levels of IGF-1, decreased catabolism and increased protein synthetis (when compared to whey and/or caseine).

I got a collection of 127 studies that show the benefits of soy protein supplementation.

1. Nagata C, Inaba S, Kawakami N, Kakizoe T, Shimizu H. Inverse association of soy product intake with serum androgen and estrogen concentrations in Japanese men. Nutr Cancer. 2000;36(1):14-18.

2. Nagata C, Takatsuka N, Shimizu H, Hayashi H, Akamatsu T, Murase K. Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men. Cancer Epidemiol Biomarkers Prev. Mar 2001;10(3):179-184.

3. Mitchell JH, Cawood E, Kinniburgh D, Provan A, Collins AR, Irvine DS. Effect of a phytoestrogen food supplement on reproductive health in normal males. Clin Sci (Lond). Jun 2001;100(6):613-618.

4. Habito RC, Montalto J, Leslie E, Ball MJ. Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males. Br J Nutr. Oct 2000;84(4):557-563.

5. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. Apr 1997;29(2):95-120.

6. Cassidy A. Potential tissue selectivity of dietary phytoestrogens and estrogens. Curr Opin Lipidol. Feb 1999;10(1):47-52.

7. Kurzer MS. Hormonal effects of soy isoflavones: studies in premenopausal and postmenopausal women. J Nutr. Mar 2000;130(3):660S-661S.

8. Castle EP, Thrasher JB. The role of soy phytoestrogens in prostate cancer. Urol Clin North Am. Feb 2002;29(1):71-81, viii-ix.

9. Gaynor ML. Isoflavones and the prevention and treatment of prostate disease: is there a role? Cleve Clin J Med. Mar 2003;70(3):203-204, 206, 208-209 passim.

10. Messina MJ. Emerging evidence on the role of soy in reducing prostate cancer risk. Nutr Rev. Apr 2003;61(4):117-131.

11. Wangen KE, Duncan AM, Merz-Demlow BE, et al. Effects of soy isoflavones on markers of bone turnover in premenopausal and postmenopausal women. J Clin Endocrinol Metab. Sep 2000;85(9):3043-3048.

12. Romagnoli E, Minisola S, Carnevale V, et al. Effect of estrogen deficiency on IGF-I plasma levels: relationship with bone mineral density in perimenopausal women. Calcif Tissue Int. Jul 1993;53(1):1-6.

13. Khalil DA, Lucas EA, Juma S, Smith BJ, Payton ME, Arjmandi BH. Soy protein supplementation increases serum insulin-like growth factor-I in young and old men but does not affect markers of bone metabolism. J Nutr. Sep

14. Aoyama T, Fukui K, Nakamori T, et al. Effect of soy and milk whey protein isolates and their hydrolysates on weight reduction in genetically obese mice. Biosci Biotechnol Biochem. Dec 2000a;64(12):2594-2600.

15. Aoyama T, Fukui K, Takamatsu K, Hashimoto Y, Yamamoto T. Soy protein isolate and its hydrolysate reduce body fat of dietary obese rats and genetically obese mice (yellow KK). Nutrition. May 2000b;16(5):349-354.

16. Volgarev MN, al. e. Evaluation of isolated soy protein foods in weight reduction with obese hypercholesterolemic and normocholesterolemic obeste individuals. Nutr Rep Int. 1989;39(61).

17. Goodman-Gruen D, Kritz-Silverstein D. Usual dietary isoflavone intake is associated with cardiovascular disease risk factors in postmenopausal women. J Nutr. Apr 2001;131(4):1202-1206.

18. Ishihara K, al: e. Effect of soybean peptide on suppression of body fat accumulation uring endurance swimming in mice. Nutr Sci Soy Protein. 1996;17:94-97.

19. Kagawa K, Matsutaka H, Fukuhama C, Fujino H, Okuda H. Suppressive effect of globin digest on postprandial hyperlipidemia in male volunteers. J Nutr. Jan 1998;128(1):56-60.

20. Kawano-Takahashi Y, Ohminami H, Okuda H, et al. Effect of soya saponins on gold thioglucose (GTG)-induced obesity in mice. Int J Obes. 1986;10(4):293-302.

21. Bosello O, Cominacini L, Zocca I, et al. Short- and long-term effects of hypocaloric diets containing proteins of different sources on plasma lipids and apoproteins of obese subjects. Ann Nutr Metab. 1988;32(4):206-214.

22. Jenkins DJ, Wolever TM, Spiller G, et al. Hypocholesterolemic effect of vegetable protein in a hypocaloric diet. Atherosclerosis. Aug 1989;78(2-3):99-107.

23. Yama****a T, Sasahara T, Pomeroy SE, Collier G, Nestel PJ. Arterial compliance, blood pressure, plasma leptin, and plasma lipids in women are improved with weight reduction equally with a meat-based diet and a plant-based diet. Metabolism. Nov 1998;47(11):1308-1314.

24. Goodman-Gruen D, Kritz-Silverstein D. Usual dietary isoflavone intake and body composition in postmenopausal women. Menopause. Sep-Oct 2003;10(5):427-432.

25. Evans EM, van Pelt RE, Racette SB, Villareal DT, Holloszy JO. Soy protein enhances body composition in postmenopausal women. FASEB J. 2004;18(5):A873.

26. Szkudelska K, Nogowski L, Szkudelski T. Genistein affects lipogenesis and lipolysis in isolated rat adipocytes. J Steroid Biochem Mol Biol. Dec 31 2000;75(4-5):265-271.

27. Szkudelska K, Szkudelski T, Nogowski L. Daidzein, coumestrol and zearalenone affect lipogenesis and lipolysis in rat adipocytes. Phytomedicine. May 2002;9(4):338-345.

28. Iritani N, Hosomi H, Fukuda H, Tada K, Ikeda H. Soybean protein suppresses hepatic lipogenic enzyme gene expression in Wistar fatty rats. J Nutr. Feb 1996;126(2):380-388.

29. Nogowski L, Mackowiak P, Kandulska K, Szkudelski T, Nowak KW. Genistein-induced changes in lipid metabolism of ovariectomized rats. Ann Nutr Metab. 1998;42(6):360-366.

30. Frayn KN. Metabolic Regulation. 1st ed ed: Portland Press; 1996.

31. Vernon RG, Barber MC, Travers MT. Present and future studies on lipogenesis in animals and human subjects. Proc Nutr Soc. Aug 1999;58(3):541-549.

32. Hellerstein MK. De novo lipogenesis in humans: metabolic and regulatory aspects. Eur J Clin Nutr. Apr 1999;53 Suppl 1:S53-65.

33. Persky VW, Turyk ME, Wang L, et al. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr. Jan 2002;75(1):145-153.

34. Forsythe WA, 3rd. Soy protein, thyroid regulation and cholesterol metabolism. J Nutr. Mar 1995;125(3 Suppl):619S-623S.

35. Barth CA, Scholz-Ahrens KE, de Vrese M, Hotze A. Difference of plasma amino acids following casein or soy protein intake: significance for differences of serum lipid concentrations. J Nutr Sci Vitaminol (Tokyo). Oct 1990;36 Suppl 2:S111-117.

36. Sanchez A, Hubbard RW. Plasma amino acids and the insulin/glucagon ratio as an explanation for the dietary protein modulation of atherosclerosis. Med Hypotheses. Aug 1991;35(4):324-329.

WOW, please everyone read these two articles, of course in near future I am going to post some studies.

http://www.t-nation.com/findArticle.do;jsessionid=94C42F10D6D1DDA3CE334D17 D197DE9F.titan?article=302poison2

http://www.bodybuilding.com/fun/author25.htm

[argonzark]

Since you went out of your way to post bb.com articles on soy, I'm surprised you didn't include the NEWEST one - http://www.bodybuilding.com/fun/willbrink4.htm - it's called "The Vindication of Soy". The main point on which soybashers built their arguments, the estrogenic compounds, has been dismissed. Of course bodybuilding is where the myths started, so it'll take a while until the common masses settle down. :)


Also argon is there a reason it needs to be soy? could it be casien? cause then you could get the greatest tasting supp. of all ...MUSCLE MILK

Yes, I'd like it to be soy because according to my research it's protein value is better than any others asides from whey. I'm allergic to whey. Plus soy has a lot more health benefits.

[PowerSwede]

WOW, please everyone read these two articles, of course in near future I am going to post some studies.

http://www.t-nation.com/findArticle.do;jsessionid=94C42F10D6D1DDA3CE334D17 D197DE9F.titan?article=302poison2

http://www.bodybuilding.com/fun/author25.htm

The first article, well, i guess if you use Soy Protein as your single source of protein intake (IE vegetarian) then the story changes since Soy Protein does not contain some of the things that animal proteins do, it has nothing to do with Soy Protein Isolate either, just soy products in general.

The second article uses theories that have been proven wrong, that is, unless you are a post-menopausal woman.

The phytoestrogens (in Soy) have no increased estrogen effect in males since they do not attatch to the estrogen receptor, it does seem to affect the amount of estrogen in the body though as it works as an anti-aromatase.


I have seen numerous studies by a couple of doctors (sponsored by the milk and dairy industry) show adverse effects of soy protein, however, i wouldn't trust any studies where the sponsors have such an obvious bias.

[satanfuneral]

Since you went out of your way to post bb.com articles on soy, I'm surprised you didn't include the NEWEST one - http://www.bodybuilding.com/fun/willbrink4.htm - it's called "The Vindication of Soy"

come on man Will Brink article isn't the newest one, L Rea is the newest one there are some other articles against soy on BB.com u can search find them.

[satanfuneral]

The first article, well, i guess if you use Soy Protein as your single source of protein intake (IE vegetarian) then the story changes since Soy Protein does not contain some of the things that animal proteins do, it has nothing to do with Soy Protein Isolate either, just soy products in general.

Dr Kaayla T. Daniel, is a noted soy researcher, I'm not saying soy is totally a bad choice, It has some undeniable benefits. there are better alternatives.

[PowerSwede]

Dr Kaayla T. Daniel, is a noted soy researcher, I'm not saying soy is totally a bad choice, It has some undeniable benefits. there are better alternatives.

We will have to agree to disagree on that.

[satanfuneral]

Gardner-Thorpe D, O'Hagen C, Young I, et al. Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stress in men. Eur J Clin Nutr. 2003;57:100–106.

[satanfuneral]

We will have to agree to disagree on that.

Yup

[Bill Gates]

Author L Rea:

Isoflavone genistein in soy protein inhibit creatine transport. Genistein inhibits tyrosine kinases which is necessary for nutrient transport.

[cody3308]

Someone posted this site on another thread to look up fruits/vegetables, here is what they same about soy: http://www.wholehealthmd.com/refshelf/foods_view/1,1523,135,00.html

[PowerSwede]

Gardner-Thorpe D, O'Hagen C, Young I, et al. Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stress in men. Eur J Clin Nutr. 2003;57:100–106.

Have you got a link to that study? I haven't been able to find even an abstract by searching for it.

Thanx.

[satanfuneral]

Have you got a link to that study? I haven't been able to find even an abstract by searching for it.

Thanx.

Yes, PowerSwede

This is a link to the index page:
http://www.nature.com/ejcn/journal/v57/n1/index.html

This is a link to study abstract:
http://www.nature.com/cgi-taf/DynaPage.taf?file=/ejcn/journal/v57/n1/abs/1601495a.html

And this is the abstract:

Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stress in men

D Gardner-Thorpe1,b, C O'Hagen2,b, I Young2,b and S J Lewis1,a,b

1Department of Medicine, University Hospital of Wales, Cardiff, Wales, UK

2Department of Clinical Biochemistry, Institute of Clinical Science, Royal Victoria Hospital, Belfast, Northern Ireland, UK

Correspondence to: S J Lewis, Department of Gastroenterology, Level 9, Derriford Hospital, Plymouth PL6 8DH, UK. E-mail: sjl@doctors.org.uk

aGuarantor: S J Lewis.
bContributors: D Gardner-Thorpe, C O'Hagen, I Young and SJ Lewis.

Abstract

Objective: We examined the effects on serum sex steroids, lipids and markers of oxidative stress of supplementing the diets of healthy male volunteers with scones made with soya flour.

Design: A randomized placebo controlled cross-over trial.

Setting: University Hospital of Wales.

Subjects: Twenty volunteers recruited by advertisement.

Interventions: Male volunteers ate three scones a day in addition to their normal diet for a period of 6 weeks. The scones were made with either wheat or soya flour (containing 120 mg/day of isoflavones). Blood was analysed for sex steroids (testosterone, dihydro-testosterone, oestradiol, oestrone, sex hormone binding globulin, albumin and the concentration of non-protein bound sex steroids were calculated), lipid profile (total cholesterol, high density lipoprotein cholesterol and triglycerides) and measures of oxidative stress (hydroperoxides, susceptibility of LDL to oxidation with copper and myeloperoxidase).

Results: The volunteers' mean age was 35.6 (s.d. 11.2) y. Total serum testosterone fell in volunteers taking the soya scones (19.3-18.2 nmol/l; 95% CI 1.01, 1.12; P=0.03). No significant changes were seen in the concentrations of the other serum sex steroids, albumin or sex hormone binding globulin throughout the study. Significant improvements in two of the three markers of oxidative stress were seen in volunteers taking soya scones. Lag time for myeloperoxidase rose from 55.0 to 68.0 min (95% CI -16.0, -3.5; P=0.009) and the presence of hydroperoxides decreased from 2.69 to 2.34 µmol/l (95% CI 0.12, 0.71; P=0.009). There were no changes seen in serum triglycerides or cholesterol.

Conclusions: We have shown that soya supplements reduce serum testosterone and improve markers of oxidative stress. These findings provide a putative mechanism by which soya supplements could protect against prostatic disease and atherosclerosis. Further dietary studies with clinical end points are warranted.