Does Soy Really Lower Testosterone Levels?

We are no strangers to the age-old myth that soy lowers testosterone levels, paving the way for issues like infertility and the dreaded "man boobs." While the claim is widely circulated on almost all sites across the net, it's important to understand the findings here are really outdated and exaggerated. 

Looking at more recent findings, you will find that the myth has been debunked. However, there is still confusion surrounding the use, and the conflicting evidence makes it hard to determine whether soy is a testosterone's friend or foe. So, I deep-dived into research to find out whether soy really lowers testosterone levels.

Things you need to know

  • Recent studies show that soy doesn't lower testosterone levels
  • Although compounds in soy can mimic the function of estrogen, new findings show it doesn't cause an imbalance in testosterone levels
  • Soy protein contains 9 amino acids, which can help regulate testosterone levels

Where is this Idea Coming From?

The "Soy Theory," as I've so aptly named it, comes from studies that involved the dissection of soy's composition. Soy is a high-protein substance that contains compounds that bind to estrogen receptors and copy the effects of the estrogen hormone. 

Now we all know, although needed, estrogen is no friend of the male body when its present at high levels. In an ideal setting, estrogen and testosterone need to be balanced to help control sex drives, erections, sperm production, and more. 

So, a component supporting the extended presence or enhanced function of estrogen, needless to say, would throw the body functions off sync. 

This would lead to symptoms similar to those seen with low testosterone, so I can see why soy is thought to lower testosterone levels. Even though some sources confirm this notion, other reports have completely debunked it. 

What do Studies Say?

I found several old studies and case reports released describing feminizing effects (lowering testosterone levels and raising estrogen levels) in men with a high soy intake. The data from these studies were re-evaluated as the years passed and modern medicine and investigation evolved. 

A 2010 analysis of over 30 studies linked to low testosterone levels and soy intake was examined in greater detail. After looking at soy intake, researchers concluded that soy intake does not alter measures of bioavailable testosterone concentrations in men. In simple, this means that testosterone levels were not affected and remained at a level of normalcy. 

Building on this study's findings, another analysis published in 2021 reviewed clinical data from 41 studies to determine whether soy or intake really affects testosterone levels. The results showed that soy intake actually had no significant effects on testosterone in any way, shape, or form. 

Further investigation found that both low and high doses of soy for different intake durations also showed no effect. This updated and expanded analysis shows that soy intake as a whole does not affect testosterone levels in men.

Soy Protein in Foods

Soy protein (plant-based protein) is derived from soybeans and is often used as an ingredient in food products. It is a reliable, sustainable source of protein with a mild flavor that complements the overall taste of different foods. 

Foods that contain soy protein are excellent sources of essential amino acids (building blocks of proteins that our bodies don't produce on their own and must obtain from our diet). Let's look at some of the common foods that have soy protein:

  • Miso
  • Tofu
  • Tempeh
  • Soy flour
  • Soy milk
  • Edamame
  • Soy burgers/sausages
  • Soy-based protein powders

Many people add soy to their diets for health benefits. Vegans and vegetarians may use it to boost the protein content in their diets.

Is Soy Protein Different?

Soy and animal protein have several differences, even though they carry many of the same benefits. The most obvious difference is the source, soy protein comes from plants, while animal protein comes from meat sources—animals.

I list other differences below:

Soy protein contains 9 essential amino acids that help with optimal functioning and testosterone levels. The presence of amino acids in animal proteins varies depending on the animal source. This means the nine amino acids are never present in a single source.

Soy protein is lower in saturated fat and cholesterol than animal protein. This makes soy protein a heart-healthy alternative to animal protein.

Soy is more likely to cause digestive discomfort, while animal protein is generally well-tolerated by most people.

Some soy products (soy protein) can be highly processed, increasing calorie intakes, while meat (animal protein) is low in calories and more fulling.

What's the Verdict?

New evidence from recent evaluations of studies and clinical trials shows that soy does not lower testosterone levels. I found that soy produces estrogen-like effects once in the body, but these effects do not affect testosterone levels or production of the hormone. Soy also provides the body with essential amino acids, which may help regulate testosterone levels.

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About the Author

Sam is a passionate health and fitness enthusiast who has been interested in supplements, fitness, and wellness for over 10 years. He is the founder of Great Green Wall - the health and wellness brand and has completed multiple fitness certificates, including personal training and nutrition certifications. Sam has been working as a personal trainer for the past three years and is dedicated to helping his clients achieve their fitness goals and lead healthier lifestyles. He believes that a healthy lifestyle is crucial to a happy and fulfilling life and is committed to sharing his knowledge and passion with others.

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