Are soy foods safe? | Mark Messina, PhD

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Soy foods have proved to be a contentious topic for decades now. With some dietary camps claiming the dangers of soy and others promoting its boundless benefits, it’s natural to be hesitant about consuming this product.

In Episode #258, I sit down with Dr Mark Messina for a deep dive into the safety and potential benefits of soy consumption. We clear the air on this plant food, evaluating what the science actually says and defining how to healthily consume it.

“Almost without exception, the safety concerns that were raised about soy, and still are today, are based on in vitro and animal studies.”

Dr Mark Messina is the Director of Nutrition Science and Research for Soy Nutrition Institute Global, co-owner of Nutrition Matters, Inc., and an adjunct associate professor at Loma Linda University. With over 30 years of experience, Dr Messina has dedicated his career to studying the health effects of soy foods and soybean components, including isoflavones. He has published over 100 articles and book chapters and given more than 700 presentations in 55 countries. Dr Messina is also the chairperson of the editorial advisory board for The Soy Connection and has organised and chaired numerous international symposia on soy’s role in preventing and treating chronic disease. He is the co-author of three books on soy, vegetarianism, and navigating vegetarian diets from a health perspective.

“Soy is a food – when you eat tofu, you’re getting isoflavones but you’re getting a heck of a lot more… We want to think of it not just as a source of isoflavones, even though that’s where a lot of the attention is, but as a source of good nutrition.”

In this conversation, Dr. Messina tackles common concerns and misconceptions about soy, addressing its safety in relation to male feminisation, breast cancer, thyroid function, and dosage. We dive deep into isoflavones, with Dr. Messina explaining how they differ from oestrogen.

An interesting fact to remember is that traditional Asian soy foods contain about 3–4 mg of isoflavones per gram of protein. In contrast, soy protein isolate and soy protein concentrate are typically processed in a way that results in a loss of approximately 80–90% of the isoflavone content. Soy flour and textured vegetable protein (TVP) made from soy flour retain the full complement of isoflavones, maintaining the same isoflavone (mg) to protein (g) ratio found in soybeans and traditional Asian soy foods.

This episode is brimming with essential information to help you comprehend the health and safety aspects of soy.

Specifically, we discuss:

  • Intro (00:00)
  • Soy throughout history (01:45)
  • Dr. Mark Messina and the Soy Nutrition Institute (6:12)
  • Industry affiliation in research (8:04)
  • Debate surrounding soy and breast cancer (18:04)
  • Isoflavones and estrogen (24:04)
  • Isoflavones, breast tissue and cholesterol (32:12)
  • Oversimplification of health information about the soy (40:39)
  • Fermented soy and equol (48:11)
  • How much isoflavones are in your soy foods? (53:16)
  • Safe upper limit of soy isoflavones intake per day (58:50)
  • Are blood tests necessary for high protein eaters? (1:01:37)
  • Soy formula and soy allergy (1:03:50)
  • Soy and thyroid Health (1:11:15)
  • Does soy affect menstrual cycle length? (1:16:12)
  • Soy consumption and migraines (1:22:54)
  • Isoflavonoid supplements (1:27:10)
  • Soy farming and the environment (1:29:10)
  • Outro (1:33:12)

I hope this conversation leaves you feeling more confident in your choices regarding soy. With decades of research and experience, Dr. Messina brings clarity to the soy debate in Episode #258, putting controversies to rest once and for all.

It’s worth noting that eight trials have explored the effects of oral isoflavone intake on skin health. The existing data is encouraging, but insufficient to draw definitive conclusions. Dr Raja Sivamani and his colleagues are currently conducting a six-month skin trial comparing 25g/day of soy protein containing 50mg isoflavones with 25g of casein in postmenopausal women. Should this trial yield significant benefits, the available data would support a compelling argument for the positive effects of isoflavones on skin health, including wrinkle reduction.

To stay up to date with Dr Mark Messina’s work, head to Here you’ll find extensive research on the health and safety of soy, as well as regular articles written by Dr Messina. You can also read some of Dr Messina’s recent, relevant articles below.

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Enjoy, friends.


More about Dr Mark Messina

Dr. Messina is the Director of Nutrition Science and Research for Soy Nutrition Institute Global, the co-owner of Nutrition Matters, Inc., a nutrition consulting company, and an adjunct associate professor at Loma Linda University.

Over the past three decades, Dr. Messina has devoted his time to the study of the health effects of soyfoods and soybean components such as isoflavones. He writes extensively on these subjects, having published more than 100 articles and book chapters for health professionals, and has given more than 700 presentations to both consumer and professional groups in 55 countries. Dr. Messina is the chairperson of the editorial advisory board of, and writes a regular column for The Soy Connection, a quarterly newsletter that reaches over 250,000 dietitians and other health professionals. He has also organized and chaired ten international symposia on the role of soy in preventing and treating chronic disease and has organized ten meetings in the United States, China, India, Brazil and Italy.

Dr. Messina is the co-author of three books: The Simple Soybean and Your Health (Avery Publishing Group, 1994), The Vegetarian Way  (Crown Publishers, 1996), and The Dietitian’s Guide to Vegetarian Diets: Issues and Applications (Aspen Publishers, 1996, Jones and Bartlett, 2004, 2010, 2022).

Additional resources

  • USDA Database for the Isoflavone Content of Selected Foods • USDA

Supporting studies

  • Estimated dietary isoflavone intake among Korean adults • PMID: 20368940
  • Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies • PMID: 33383165
  • Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data • PMID: 33775173
  • Perspective: Soy-based Meat and Dairy Alternatives, Despite Classification as Ultra-processed Foods, Deliver High-quality Nutrition on Par with Unprocessed or Minimally Processed Animal-based Counterparts • PMID: 35325028
  • Perspective: Soybeans Can Help Address the Caloric and Protein Needs of a Growing Global Population • PMID: 35600829
  • Plant-Based Meat Alternatives Can Help Facilitate and Maintain a Lower Animal to Plant Protein Intake Ratio • PMID: 36906147
  • Soybean oil lowers circulating cholesterol levels and coronary heart disease risk, and has no effect on markers of inflammation and oxidation • PMID: 34171740
  • The health effects of soy: A reference guide for health professionals • PMID: 36034914

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