Soy: Debunking Its Bad Reputation

Misconceptions about soy being a hormone disruptor linger in thin air... It is time for a scientific update.

Takeaways

• Soybeans contain a type of phytoestrogen called isoflavones, which are natural compounds found in many plants

• There is no significant effect of isoflavones on reproductive hormone levels in men and women

• Evidence does not support classifying isoflavones as endocrine disruptors

• Soy is a nutrient-dense form of protein

---

Soybeans: A misunderstood legume

👨🏽 I once heard a friend say, ‘I don’t eat soy products because of their estrogen content.’ It was one of his arguments for not being on a plant-based diet and not providing his son with soy-derived products. He was concerned about his manliness… Understandable. But here's the truth. Soybeans are composed of phytoestrogen called isoflavones, and contrary to popular belief, these molecules have no adverse effects on testosterone levels. And guess what? Other common foods such as beans, oats, barley, rice, coffee, apples, and carrots have phytoestrogen, too.

🌱 Beware of the phyto prefix in the word phytoestrogen. Phyto, in Greek, means ‘plant,’ followed by the word estrogen, which is the hormone responsible for developing and regulating the female reproductive system (and secondary sex characteristics). No wonder why he was so concerned… Reality check? Phytoestrogen only sounds like estrogen but is not as it is structurally distinct from human estrogen hormones.

Credits: Midjourney.

🤔 Chemistry aside, my brain was puzzled by his questioning. According to research, the mean isoflavone intake in Japan among older adults ranges from approximately 30 to 50 mg per day— or 6 to 11 g of soy protein per day.¹ And it does not seem that there are more hormonal issues in the male population in Asia… On top of that, in 1999, the US Food and Drug Administration (FDA) concluded that soy protein was safe when consumed at a level of 25 g per day, and it even supported the reduction of the risk of coronary heart disease.²

🔎 Why has isoflavone been embroiled in controversy?

1️⃣ It began with research conclusions on female animals’ infertility impairment in sheep in 1946 and cheetahs in 1987. This initial research sparked concerns about the potential effects of isoflavones on human health.

2️⃣ Next, isoflavones seemed to stimulate mammary tumor growth in mice and human studies in the late 90s.

3️⃣ In subsequent years, concerns expanded to include thyroid and cognitive dysfunctions. Soy was “routinely referred to” as an endocrine disruptor (i.e., any external agent that interferes with our natural hormones, causing adverse effects on an organism's normal development).

At this point, you may be wondering about where these claims stand today (2024).

👍 Here we go with the good news:

⚛️ Science moved on. Many statements from previous research have been revisited and reevaluated, and new conclusions have emerged. Remember, science evolves thanks to stricter research guidelines, novel technology to guide experiments, and new approaches to tackle previous or new hypotheses (e.g., today, it is well-known that isoflavone metabolism differs between rodents and humans, making extrapolation from mice to us, particularly problematic. The above concerns were primarily based on rodent studies).

☝️ The (less) good news?

Many people still hold on to certain old beliefs. That is understandable, especially in our era of overwhelming information. Most folks following a plant-based diet, in which soy products are recurrent, have probably dug into the updated soy status. If this isn't your case, this article is just for you.

🤓 To bring you the current state of knowledge, I dove into a critical review from 2022.³ If there is only one main conclusion to keep in mind, this is it:

🟢 Based on research in adults, the evidence does not warrant classifying isoflavones (or soy foods) as endocrine disruptors.

🥒 Conclusions sliced-up:

* “Adverse effects have not been reported in long-term trials where study participants consumed >100 mg daily of isoflavones. Instead, this figure is suggested because there is no historical precedent for habitual consumption higher than this amount.”(3) ** “Given the low concentration of isoflavones in breast milk and the high in-utero estrogen concentrations, adverse effects would not be expected. However, the historical precedence of Asian women consuming soy during pregnancy and lactation provides a considerable measure of comfort.”(3)

---

👀 For those who are curious about the considerations of this technical review:

• 417 reports were included in the analysis out of 2038 reports identified (from inception through January 2021)

• The paper focuses primarily on (1) clinical data and secondarily (2) observational data

• Soy consumption is extremely low among Western cohorts, so the focus is on studies involving Asian cohorts

• The search was restricted to humans (i.e., in vitro and animal studies were excluded from the analysis)

---

🫛 With this said, have you ever feared eating soy products? Did this article clarify some of your burning questions? Leave a comment.

🧐 Until the following Monday, stay curious!

---

Inspiration corner

I regularly eat tofu steaks. A brand in France I love:

Yum!

Tofu steaks are my best companion for days when I am low on “cooking energy” or when I return from a long run. It fits perfectly in different meals:

🍔 As my burger “patty”

🍛 Alone as a “steak” accompanied by veggies and legumes

🥘 Chopped in cubes and added to my wok

On another note:

🤯 A type of tofu that blew my mind (and I discovered it only a couple of years ago) is a soft version— tofu soyeux (in French). You can use it to replace eggs in quiche, for example. Mix the soft tofu (~ 200 mL) with chickpea flour (~ 40 g) for a high-protein mixture. Add this mixture as the first layer on your pre-baked dough, followed by your veggie topping.

👀 I often make my quiche with the produce sitting in my fridge, so I don’t quite have “the recipe” to share with you today. Sorry! I have this intuitive mindset in the kitchen. I mix things, and it turns out pretty good 90% of the time. I must be motivated to follow a recipe... But if you need a nudge, I will gladly guide you.

😋 Unless you have a wonderful recipe to share? Let me know in the comments.

Out-of-the-blue topping: Sundried tomatoes, leek, red onions, and pickles.

Last but not least, it is worth remembering that soy is a nutrient-dense form of protein.

✌️At least 2x more nutrient-dense than meat or eggs (according to the ANDI score created by Dr. Joel Fuhrman). The scoring system considers the micronutrients per calorie of foods (based on 34 nutritional parameters, ranging from 1000 to 1). It is interesting to see foods from a ‘nutrient perspective.’ Why? Leafy greens are on the top [Guess what? Kale is a winner! I love kale 🫶], and animal products are at the bottom of the scale... Curious? Check out the scale here.

💪 By the way, are you looking into building lean mass? Yep. Soy is as effective as animal-based proteins. Additionally, long-term soy intake as part of a healthy diet provides cardiometabolic advantages in older adults.⁴

🙌 Bottom line: Soy provides you with proteins plus micronutrients!

To keep in mind.

Xoxo,

Fernanda

PS1: Other articles you might find interesting:

• Deciphering Protein Priorities: Opting for Quality or Quantity?

• Reversing Aging: The Plant-based Diet Approach

• Red Beets: Good For You And For Your Exercise Performance

• Food As Medicine: An Old Concept Undergoing a Renaissance

PS2: Find my archive here! Do you know that clicking in the heart or leaving a comment helps others discover this Newsletter? Thank you for supporting my work.

1. Messina, M., et al., Estimated Asian adult soy protein and isoflavone intakes. Nutrition and Cancer (Journal). 2006 (link)

2. Food Labeling: Health Claims; Soy Protein and Coronary Heart Disease. Food and Drug Administration. 1999 (link)

3. Messina M. et al., Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data. Critical Reviews in Food Science and Nutrition (Journal). 2022 (link)

4. Tischmann L. et al., Longer-term soy nut consumption improves vascular function and cardiometabolic risk markers in older adults: Results of a randomized, controlled cross-over trial. Clinical Nutrition (Journal). 2022 (link)