Soy intake is linked with a wide variety of health benefits. Evidence supporting specific benefits ranges from solid (heart disease) to speculative (prostate cancer). One proposed benefit that has received scant attention is the effect of soy on skin health. There is intriguing research suggesting that even modest amounts of soy favorably affect a number of skin parameters. Not surprisingly, definitive data have yet to be published but given all of the money spent on cosmetics in the United States – an obvious indication of the public’s interest in having beautiful skin – you might think more attention would have been paid to studies showing, for example, that soybean isoflavones reduce wrinkles.
A newly published study from Japan adds to evidence that soy does, indeed, exert skin benefits. For this study, 60 Japanese premenopausal women were randomly allocated to receive either 100 ml fermented soymilk containing Lactobacillus casei Shirota twice per day or non-fermented soymilk twice daily.1 Questionnaires aimed at assessing the condition of skin were filled out at baseline, after 8 weeks of consuming soymilk, and 4 weeks after stopping soymilk consumption. Samples of the stratum corneum on the inner forearm taken at baseline and after 8 weeks of soymilk consumption were used for morphological analysis. In short, the results showed that when compared to baseline, all six questions on the questionnaires showed significant improvement in the condition of the skin. After stopping soymilk, the improvements slowly dissipated. The results of the morphological analysis were consistent with the questionnaires. Thus, there were both subjective and objective measurements indicating soymilk improved skin health. There were, however, no differences between the effects of the two types of soymilk on the skin.
That both subjective and objective measurements indicated an improvement in skin health is clearly a strength of this study. However, there was no true control group as all women consumed soy. The amount of isoflavones ingested by the women wasn’t reported in the paper. Ordinarily, 200 ml of soymilk would contain only about 20 mg isoflavones although the lead author (personal communication) indicated the soymilk provided 60 mg.
A paper published in 2014, but involving postmenopausal women, supports the findings of this Japanese study. In a 2014 study, women received daily either a placebo or a cocktail of biologically active compounds that included isoflavones (40-70 mg) but also vitamins E and C, lycopene and omega-3 fatty acids.2 Compared to placebo, after 14 weeks, there was a statistically significant decrease in wrinkles and wrinkle depth (average decrease about 10%) in the treated group. Women with more wrinkles at baseline experienced the most benefit. While this study did include a true placebo, it isn’t possible to directly ascribe the benefits to isoflavones because they weren’t given in isolation. However, the improvement in wrinkles was due to an increase in collagen synthesis. Among the various compounds in the cocktail, only isoflavones had been shown previously to increase collagen synthesis.
Given their results, the question arises as to why the two above-cited studies haven’t received more attention, especially when there are other studies supporting their findings. Partly this may be because of disagreements over which outcome variables have been studied and which methods of measurement have been used to study them.
European researchers recently pointed out that despite evidence suggesting a protective role for several nutrients and foods in the maintenance of skin function, all requests for authorization to use health claims related to the maintenance of skin function presented to the European Food Safety Authority (analogous to the FDA) have received a negative opinion.3 These researchers found with respect to wrinkles that “even if skin wrinkles are a reliable parameter of skin structure, they are an indirect parameter of skin hydration. For this reason, skin wrinkles are not appropriate to be used alone for the substantiation of health claims in the context of protection of the skin against dehydration. However, they can be used as supportive evidence when appropriate outcome measures are also considered.”
Hopefully, with a better understanding of precisely how to assess changes in skin health– and with appropriately designed studies– in the not too distant future it may be possible to add improvements in skin health to the list of benefits ascribed to soyfoods.
- Nagino T, Kaga C, Kano M, et al. Effects of fermented soymilk with Lactobacillus casei Shirota on skin condition and the gut microbiota: a randomised clinical pilot trial. Beneficial Microbes. 2017:1-10.
- Jenkins G, Wainwright LJ, Holland R, Barrett KE, Casey J. Wrinkle reduction in post-menopausal women consuming a novel oral supplement: a double-blind placebo-controlled randomized study. Int J Cosmet Sci. 2014;36:22-31.
- Martini D, Angelino D, Cortelazzi C, et al. Claimed Effects, Outcome Variables and Methods of Measurement for Health Claims Proposed Under European Community Regulation 1924/2006 in the Framework of Maintenance of Skin Function. Nutrients. 2017;10.