Soy, a type of legume, is quite the polarizing food. Soy is an important component in many Asian dishes, and has been consumed for thousands of years. Unfortunately, significant amounts of misinformation have been spread about soy over the last several decades, leaving many to wonder if soy is a healthy choice or not. Many have been told to stay away from soy due to the risk of breast cancer or feminizing effects, among other concerns. Let’s better understand what soy has in it - and what it doesn’t - so you can make an informed choice!

What’s in soy?

Whole soy - such as edamame (whole soy beans) - and minimally processed soy products - such as tofu, tempeh, and soy milk - are great sources of protein. Soy contains all of the essential amino acids, with essentially the same protein bioavailability as animal protein. It is one of the best sources of plant based protein. Compared to other legumes, it is additionally much higher in heart healthy fat and lower in carbs.

Soy also contains a very high amount of vitamins and minerals (including potassium, iron, and vitamin B), fiber, phytosterols, and omega-3’s (polyunsaturated fatty acids). Importantly, it does not contain cholesterol and is low in saturated fat.

Does soy contain estrogen?

No. Soy contains isoflavones aka phytoestrogens, which are “estrogen-like.” Isoflavones are a special type of phytonutrients that actually bind to estrogen receptors differently in the body, thus having both pro- and anti-estrogen like effects. Additionally, phytoestrogens have a very weak affinity to the estrogen receptor and so are much less potent than actual estrogen.

Large meta-analyses have found no correlation with soy consumption in humans and feminizing effects such “man boobs,” or clinically meaningful changes in sex hormones. Studies that found such an association were conducted on rats. Luckily, we are not rats.

Is all soy GMO?

While it is true that most of soy in the United States is GMO (genetically modified), by far the largest consumer of GMO soy is actually livestock.

GMO soy is also used to make soybean oil and other emulsifiers, which is frequently in packaged and processed foods.

Non-GMO whole soy foods such as tofu, tempeh and soy milk are widely available in stores, and they are clearly labeled non-GMO. Should you wish to avoid GMO soy in your whole soy products, it is quite easy to do so.

Is soy heart healthy?

Yes!

A very, very large review was recently published summarizing the data from 114 meta-analyses including both clinical trials and observational studies in humans. This study found that those consuming more soy had a 17% reduced risk of heart disease and an 18% reduced risk of stroke. Those consuming fermented soy (ie tempeh, miso, natto) additionally reduced the risk of dying from cardiovascular disease.

This is not surprising given the nutritional properties of soy as described above. We know from randomized controlled trials that whole soy products lower cholesterol, a major risk factor for heart disease, and as such, is a major component of an evidence-based, cholesterol lowering program called the Portfolio diet - which I wrote about here. Soy has also been shown to improve vascular function and alter the microbiota to favor species with anti-inflammatory properties.

Since that analysis, another large US-based cohort study reported very similar reductions in cardiovascular endpoints. Interestingly, in women in this study, those who seemed to benefit the most were premenopausal women or postmenopausal women who were not taking hormonal replacement therapy.

Soy is also additionally associated with a reduced risk of diabetes, cancer (breast, ovarian, prostate, colorectal, and lung cancer), and menopausal symptoms.

Many national guidelines, such as the American Cancer Society, recommend whole or minimally processed soy foods as part of a healthy diet.

So should I eat soy?

If you enjoy it, yes!

If you don’t, no worries - there’s just no reason to be fearful of it. The data demonstrating soy as harmful is in animals, case reports of humans consuming massive quantities daily, or by studying highly processed soy products such as that found in soy protein powders.

Soy can be a very nutrient dense, heart-healthy addition to the diet - both by displacing animal-based protein sources, which are high in saturated fat and cholesterol, as well as by their inherent heart healthy properties. Soy is high in heart healthy fats, protein, and numerous vitamins and minerals, while being low in saturated fat and carbs.

Consider reaching for whole or minimally processed soy sources up to a few servings a day, particularly if you are trying to lower your cholesterol. Calcium set tofu or tempeh is a great swap for animal proteins in many dishes including stir frys and grain bowls. Just be sure to season it appropriately - like chicken, it doesn’t have much flavor on it’s own and marinates beautifully. You can also swap out a cow’s milk with a calcium fortified soy milk for a nearly identical nutrient profile - just look for one free of additional added sugar and emulsifiers.

The data is mixed with regards to isoflavone supplements or soy protein isolate and so, as with most foods, I typically recommend use of the whole food rather than processed formulations.