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Soy protein

Types, nutrients, benefits, drawbacks, and more

Soy protein is a controversial food — while some think of it as a nutritional powerhouse, others see it as an enemy to health. This article tells you whether soy protein is good or bad for you.

Evidence-based
This article is based on scientific evidence, written by experts, and fact-checked by experts.
We look at both sides of the argument and strive to be objective, unbiased, and honest.
Last updated on September 6, 2022, and last reviewed by an expert on August 11, 2022.

Soy protein is the primary protein in soy products, such as tofu, tempeh, soy milk, and other soy-based dairy and meat alternatives.

It can also be found in soy protein powder, which you can use to supplement a workout routine or add more protein to your diet.

For people following a plant-based diet or who don’t eat dairy, soy foods often serve as a significant source of protein, vitamins, and minerals.

Although some people believe soy to be a nutrient powerhouse, others question whether it poses unwanted side effects.

This article examines the evidence to determine whether soy protein is an excellent addition to your diet, then offers a few ideas for how to enjoy it.

Types of soy foods

Soy comes in various forms, which have varying nutrients and health effects.

Minimally processed soy

On one end of the spectrum are whole or minimally processed soy foods, such as tofu, tempeh, and whole soybeans — also called edamame.

More processed soy

Soy milk is slightly more processed. To make soy milk, soybeans are cooked in water, pulverized, and pressed to remove the solids and fiber. Manufacturers may add other ingredients and nutrients.

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You’ll find soy protein powder or soy protein isolate on the most highly processed end of the spectrum. They’re often used as ingredients in certain packaged foods like protein bars.

Soy protein isolate powder is made from defatted soybean flakes that have been washed in either alcohol or water to remove the sugars and fiber. They’re then dehydrated and powdered.

Summary: Soy foods fall into a spectrum of minimally to highly processed. They include whole soybeans, tofu, tempeh, miso, natto, soy milk, and isolated soy protein powder.

Nutrition facts of soy foods

The nutritional makeup of soy foods varies depending on which one you’re eating.

Overall, soy is a good source of protein, fiber, and vitamins and minerals like calcium, iron, magnesium, and zinc. It contains some unsaturated fat and is free of cholesterol.

This list shows the nutrition facts for one serving of a few types of soy foods:

Firm tofu, 1/2 cup (126 grams)

Soy milk, 1 cup (240 mL)

Soy protein powder, 1 ounce (28 grams)

As you can see, soy foods’ fat, fiber, carb, and mineral counts fall into a wide range.

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Soy protein isolate packs the most protein per serving, which makes sense because it’s processed to be a concentrated source of this nutrient.

Summary: Soy is generally a good source of protein, though the specific nutrient makeup depends on the form. For instance, soy protein isolate has much more per serving than tofu or soy milk.

Does soy food offer amino acids?

One of the most common criticisms of plant proteins is that they don’t contain all of the essential amino acids your body needs to make protein. However, this is a misconception — as is the idea that plant proteins are inferior to animal proteins.

All plants contain all nine essential amino acids, but some only offer very limited amounts. For instance, in most grains and cereals, lysine only occurs in small amounts.

This just means that you should include other sources of lysine in your diet, such as soy, so your body can make all the protein it needs. All you need to do is enjoy a diverse diet, which is good for your health.

Soy foods not only contain all nine essential amino acids but also offer ample amounts of each, making soy similar to animal proteins in this way.

Summary: Soy contains all nine essential amino acids in similar amounts, whereas other types of plant proteins are often low in at least one essential amino acid.

Health benefits of soy foods

Soy may aid heart health, cancer risk, and blood sugar levels. These benefits are largely attributed to soy’s health-promoting compounds like phytosterol, saponins, lecithin, phytic acid, and isoflavones, in addition to its nutrition profile.

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Soy foods may protect heart health

Soy foods appear to have positive effects on heart health.

In one review of 35 studies, soy intake lowered LDL (bad) cholesterol and raised HDL (good) cholesterol.

This matters because high levels of blood fats like LDL and triglycerides are associated with a higher risk of heart disease, stroke, and heart attack.

Soy foods may offer anticancer benefits

Many observational studies suggest that a high soy diet protects against cancer risk, outcomes, and even recurrence. Still, it’s important to note that these benefits are tied primarily to whole and minimally processed soy foods, not supplemental soy protein isolate.

One study examining the effects of dairy and soy on breast cancer risk associated high intakes of dairy — but not soy — with greater breast cancer risk.

Another review found a statistically significant link between soy food intake and a lower risk of prostate cancer.

Plus, while more research is needed, one meta-analysis of 12 studies associated soy food intake before and after a breast cancer diagnosis with a reduced risk of cancer recurrence.

Finally, older research notes that soy has antioxidant properties and may promote cancer cell death and inhibit the growth of blood vessels in tumors.

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Soy foods may support blood sugar control

Eating soy foods is associated with better blood sugar control, which is especially important for people who have — or are at risk of — diabetes.

Some research indicates that fermented soy foods may be particularly effective in helping minimize the effects of diabetes.

One meta-analysis of 18 studies associated eating soy products, including soy protein and soy isoflavones, with a lower risk of type 2 diabetes.

Another meta-analysis of 15 studies also tied dietary intake of tofu, soy protein, and soy isoflavones to a lower risk of this disease, though more research is needed.

Summary: Eating whole and minimally processed soy foods appear to support heart health, cancer risk, and blood sugar management. These benefits don’t appear to apply to soy protein isolate.

Potential downsides of soy foods

Some people are concerned about soy, particularly compounds called antinutrients and phytoestrogens. Others worry that soy foods are genetically modified.

Antinutrients

Soy contains phytates, plant compounds often categorized as antinutrients (alongside lectins, oxalates, and tannins). Antinutrients may reduce the availability of minerals like calcium, iron, and zinc.

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However, phytates aren’t harmful unless your diet is severely imbalanced and you rely on soy protein as your primary source of iron and zinc.

Plus, studies show that your body’s absorption of these minerals from plant foods is comparable to animal products.

Furthermore, you can reduce soy foods’ antinutrients by soaking, fermenting, and heat cooking.

Phytoestrogens

Many people avoid eating soy protein due to its phytoestrogen content, as there’s concern that this compound can disrupt natural hormone levels in your body.

Phytoestrogens are compounds that occur naturally in plants, notably soy. They have estrogen-like properties that bind to estrogen receptors in your body. As such, some people worry that soy promotes breast cancer or even affects male reproductive hormones.

However, current evidence does not show soy products to either promote breast cancer or impair male reproductive hormones.

Genetic modification

Most soy foods grown worldwide are genetically modified (GMO), meaning that they have been genetically altered to be resistant to certain herbicides.

Some people are concerned about the unknown long-term health effects of GMO foods. Most current research on GMOs’ health effects is conflicting, and long-term studies are needed.

Still, one older study found that GMO soybeans contained more pesticide glyphosate residues than organic soybeans. This is concerning as glyphosate is likely carcinogenic. It may also promote inflammation and interfere with immune health.

Regardless, non-GMO soy products are available at most grocery stores. If you want to avoid GMO soy, you can opt for certified organic products, as this prohibits genetic modification.

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Summary: While antinutrients, phytoestrogens, and genetic modification are common concerns regarding soy products, evidence shows that soy foods are mainly safe. You can always opt for non-GMO or organic soy products if you desire.

Soy protein may aid in weight loss

Including soy protein in your diet may support weight loss.

Studies indicate that high protein diets are effective for weight loss, even without limiting calories or nutrients.

Furthermore, research has shown that high protein diets based on plant protein are equally effective for weight loss as diets based on animal sources.

In a 12-month study, 71 adults with overweight or obesity ate three servings of either soy or non-soy protein daily. Body weight fell in both groups, but soy also improved body composition and heart health — and was as effective for weight loss as non-soy protein.

Another 12-week study found similar results with soy protein powder. Both soy and non-soy meal replacements resulted in an average weight loss of 17.2 pounds (7.8 kg) in older adults with abdominal obesity.

All the same, more research is needed.

Summary: If you’re trying to lose weight, a high-protein diet based on soy protein appears to be as effective as one based on animal proteins.

How to enjoy soy protein

Soy is incredibly versatile and easy to add to your diet. Some easy ways to prepare it include:

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Summary: Soy foods are versatile and can be used like animal proteins. Enjoy various forms of soy in sandwiches, soups, salads, side dishes, entrées, and smoothies.

Summary

Soy is a good protein, fiber, and essential vitamins and minerals source. It also contains health-promoting compounds like isoflavones.

Though you may have heard concerns about soy’s GMO status or phytoestrogen content, most scientific evidence suggests that there’s no need to avoid soy products.

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Eating soy protein — especially whole and minimally processed foods like edamame, tofu, and tempeh — may offer numerous benefits for heart health, blood sugar control, weight loss, and even cancer risk and recurrence.

Quick tip

Soy is an inexpensive, versatile source of protein whether or not you follow a plant-based diet. It’s easy to make a tofu scramble by crumbling extra firm tofu into a skillet and cooking with olive oil, chopped greens, veggies, and seasonings.

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