Have you ever tasted tofu?
Q: Did you see that an Asian diet helps ward off the effect of menopause?
A: An “Asian diet?” Do they mean Afghan, Punjabi, Bengali, Goan, Kirghiz, Uighur, Malaysian, Thai, Vietnamese, Lao, Korean, Beijing, Sichuan, Shanghai, …
Q: Ok, yes, I get the point. Did you see that a diet with lots of soy, similar to Japanese and some Chinese diets, helps prevent fractures and heart attacks?
A: The story about phytoestrogens? Yes.
Q: And do they?
A: Hard to tell.
Q: Was it mice again?
A: No, this was a proper randomised trial in women. It’s just they didn’t measure fractures or even bone density.
Q: What did they measure?
A: The concentration of two proteins that are involved in bone formation
Q: How reliable is that?
A: By the standards of purely biochemical laboratory markers, not bad. An article in the newsletter of the American Association for Clinical Chemistry said “Commercially available immunoassays for all the markers are reasonably bone-specific and reflect bone turnover in postmenopausal osteoporosis and following anti-resorptive therapy.”
Q: I can sense a ‘but’ coming on here
A: The story doesn’t say how big the changes were, and since this is only a forthcoming conference presentation, it’s hard to find out much detail. The abstract is here.
Q: How does it work?
A: Soy beans contain chemicals that weakly stimulate oestrogen receptors and so have some of the effects of oestrogen.
Q: Oh, like the dangerous endocrine disrupting pollutants I keep hearing about?
A: No, those are synthetic chemicals, not natural dietary components.
Q: That’s a remarkably good poker face you have
A: Can we move on?
Q: Ok, so what about the cardiovascular risk factors? The story says “They were also less at risk of heart disease, which oestrogen is also thought to protect against.” Did they measure heart disease?
A: No, they measured “cardiovascular risk markers”
Q: Does oestrogen improve these “risk markers”?
A: Yes, it does.
Q: Wait, wasn’t there a big trial of oestrogen and heart disease risk?
A: You mean the Women’s Health Initiative? Yes, there was.
Q: Did they see these improved risk markers?
A: Yes
Q: And a reduction in fractures?
A: Yes.
Q: But they didn’t see a reduction in heart disease, did they?
A: No, an increase. Over all, serious chronic disease was very slightly worse with oestrogen supplements.
Q: So why do we expect soy to be different?
A: An excellent question
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »