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Introduction
The popularity of soy foods and soy-based products has been increasing in recent times. This has been particularly the case as a dairy alternative, with people switching to using soy ‘milk’ and soy-based yogurts and cheese. Additionally, soy has become popular as a meat alternative in a variety of dishes for those looking to reduce meat intake. Soy foods such as tofu can be used in recipes in place of meat, and soy-based ‘meat alternatives’ that are vegetarian and vegan friendly have been developed.
With this increased prevalence, there has been some debate about the health effects of consuming soy foods and products. On one side, there have potential benefits highlighted of inclusion of soy in the diet. It contains phytoestrogens, which may have beneficial effects. Additionally, it is low in saturated fat, and so is potentially beneficial when used in place of saturated fat-rich foods.
However, some have claimed that the phytoestrogens (isoflavones specifically) in soy can be a cause for concern due to the ability of these compounds to mimic the effects of the hormone oestrogen. One common claim is that high soy intake is detrimental for men particularly, as it is “feminizing”; causing gynecomastia, loss of libido and erectile dysfunction.
So what is the truth? Is soy a health food? A harmful endocrine disruptor? Or simply neutral? In this episode we dive into the research and look at the evidence to date tells us about these questions. We consider two big health outcomes in particular; cardiovascular disease and breast cancer. And then final discuss what this means practically for our dietary choices.
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- [01:44]Soy: Nutrient profile & metabolism
- [19:00]Soy & men’s health: Is soy “feminizing”?
- [38:24]Breast cancer
- [53:51]Cardiovascular disease & menopause
- [1:10:56]Pragmatic recommendations
- [1:17:30]Danny’s “Key Ideas”
The Hosts
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Dr. Alan Flanagan has a PhD in nutrition from the University of Surrey, where his doctoral research focused on circadian rhythms, feeding, and chrononutrition.
This work was based on human intervention trials. He also has a Masters in Nutritional Medicine from the same institution.
Dr. Flanagan is a regular co-host of Sigma Nutrition Radio. He also produces written content for Sigma Nutrition, as part of his role as Research Communication Officer.
Danny Lennon has a master’s degree (MSc.) in Nutritional Sciences from University College Cork, and he is the founder of Sigma Nutrition.
Danny is currently a member of the Advisory Board of the Sports Nutrition Association, the global regulatory body responsible for the standardisation of best practice in the sports nutrition profession.
Key Ideas
The three key ideas highlighted for this episode were:
- Impact of phytoestrogens and their metabolites
- Meta-point about research appraisal
- Can I eat soy regularly?
1: Impact of phytoestrogens and their metabolites
Perhaps the most interesting aspect to consider about soy as a nutrient source, is that it contains isoflavones, a group of polyphenol compound. Isoflavones are phytoestrogens, meaning they are compounds that can behave like estrogens.
One of the subtypes of isoflavone, daidzein, undergoes metabolism by the gut bacteria, producing metabolites, most importantly S-equol. Equol has an affinity for binding to estrogen receptors that is higher than that of the parent isoflavone, daidzein.
