Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis.

Some studies suggest that phytoestrogens, especially those from soy and its products, have a significant effect on weight loss, both in animal and in humans studies.

Learn about soy's negative effects on what it means to be male.

Soy contains protein, isoflavones and fiber, all of which provide health benefits. A study in older Japanese men that consumed soy daily found that as soy intake increased the serum concentrations of estradiol decreased but also found soy intake had a small effect on levels of estrone 3. This protective effect is less dramatic for women who eat less soy or who start eating soy later in life.

Fertility Other concerns include whether soy has a negative effect on reproductive health.

It's been touted as a health food, but there may be a dark side. This is thought to be because the isoflavones in soy can act like estrogen in the body, and increased estrogen has … However, there have been some concerns that soy might lower a man’s testosterone levels.

Although soy and estrogen studies may be a primary point of interest, they're not the only pathway to understanding how this plant product acts on the human body. Learn about soy's negative effects on what it means to be male.

But scientists are still untangling soy’s impacts on hormonal health.

With multiple mechanisms at work in a product that is often studied with contradictory methods, using nonstandardized soy derivatives, it's little wonder that the results can be contradictory and confusing. Still, McManus says it's okay to eat whole soy foods — like soy milk, edamame, and tofu — in moderation, several times per week.

So stay away from soy isoflavone supplements and foods made with textured vegetable protein and soy protein isolate, found in many protein powders and nutrition bars.

However, that does not appear to be the entire explanation, as diet effects may also benefit people with estrogen-receptor-negative cancers.

2010 Aug;94(3):997-1007. Some researchers have suggested that these compounds somehow block the effects of estrogens. Our world-class experts have spent the last 15 years working 1-on1 with thousands of nutrition coaching and certification clients. It's been touted as a health food, but there may be a dark side. Research has shown that soy can lower cholesterol.
Phytoestrogens, which are present in soy products, have the ability to bind to receptors like estrogen.

With this research and experience, we've uncovered an exact formula for getting results. The studies each used a specific type of soy, such as soymilk, tofu, soy grits, isolated soy protein (up to 56 grams), supplemental isoflavones, or a mix of traditional and processed soy.

Soybeans are a complete protein source and a dietary staple in many cultures. Sign up for our email newsletter for the latest science news. Studies show that a lifelong diet rich in soy foods reduces the risk of breast cancer in women. A randomised controlled clinical trial by Allison conducted on 74 obese people stated that there was a significant weight loss after administration of soy-based meal replacement formula. Some studies have suggested a link between soy or isoflavone supplements and an increased risk of breast cancer in women who have a family or personal history of breast cancer or thyroid problems.
With multiple mechanisms at work in a product that is often studied with contradictory methods, using nonstandardized soy derivatives, it's little wonder that the results can be contradictory and confusing.