What Is Soy Protein? All You Need to Know

Soy comes in a wide variety of forms, all of 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.

• Tofu. This popular plant-based protein is made from condensed soy milk in a process that resembles cheesemaking. It’s shaped into spongy, solid white blocks of soy curds that come in silken, firm, and extra firm textures.
• Tempeh. This dense, nutty cake or patty is made by partially cooking whole soybeans, then fermenting them with the mold Rhizopus oligosporus. It has a firmer texture than tofu.
• Natto. This Japanese sticky breakfast dish is made by fermenting soybeans with Bacillus subtilis var. natto. It’s commonly served over rice.
• Miso. This flavorful paste is used in soups and other recipes. It’s made from fermented soybeans and barley or rice malt.

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.

On the most highly processed end of the spectrum, you’ll find soy protein powder or soy protein isolate. They’re often used as an ingredient 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.

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

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

This chart shows the nutrition facts for one serving of a few types of soy foods (1, 2, 3):

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

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 protein per serving than tofu or soy milk.

One of the most common criticisms of plant proteins is that they don’t contain all of the essential amino acids, which 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, lysine only occurs in small amounts in most grains and cereals (4).

This just means that you should include other sources of lysine in your diet, such as soy, so that 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 in general.

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 (5).

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.

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 (6).

May protect heart health

Soy foods appear to have positive effects on heart health (7).

In one review of 35 studies, soy intake lowered LDL (bad) cholesterol and raised HDL (good) cholesterol (8).

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 (9).

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 (10).

One study looking at the effects of dairy and soy on breast cancer risk associated high intakes of dairy — but not soy — with greater breast cancer risk (11).

Another review found a statistically significant link between soy food intake and a lower risk of prostate cancer (12).

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 (13).

Finally, older research notes that soy has antioxidant properties and may promote cancer cell death and inhibit the growth of blood vessels in tumors (14).

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 (15).

Some research indicates that fermented soy foods may be particularly effective in helping minimize the effects of diabetes (16).

One meta-analysis of 18 studies associated eating soy products, including soy protein and soy isoflavones, with a lower risk of type 2 diabetes (17).

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 (18).

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.

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

Antinutrients

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

However, phytates aren’t harmful unless your diet is severely imbalanced and you rely on soy protein as your main source of iron and zinc (19).

Plus, studies show that your body’s absorption of these minerals from plant foods is comparable to those from animal products (20).

Furthermore, you can reduce soy foods’ antinutrients by soaking, fermenting, and heat cooking (19).

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 (21).

However, current evidence does not show soy products to either promote breast cancer or impair male reproductive hormones (10, 20, 21, 22).

Genetic modification

The majority of soy foods grown around the world are genetically modified (GMO), meaning that they have been genetically altered to be resistant to certain herbicides (23).

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 (24).

Still, one older study found that GMO soybeans contained high residues of the pesticide glyphosate, compared with organic soybeans. This is concerning as glyphosate is likely carcinogenic. It may also promote inflammation and interfere with immune health (25, 26).

Regardless, non-GMO soy products are available at most grocery stores. If you want to avoid GMO soy, you can opt for products that are certified organic, as this prohibits genetic modification (27).

Summary

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

Including soy protein in your diet may support weight loss.

Studies indicate that high protein diets are an effective tool for weight loss, even without limiting calories or nutrients (28, 29, 30).

Furthermore, research has shown that high protein diets based on plant protein are equally effective for weight loss as diets based on animal sources (31, 32).

In a 12-month study, 71 adults with overweight or obesity ate 3 servings of either soy or non-soy protein daily. Body weight not only fell in both groups, but soy also improved body composition and heart health — and was as effective for weight loss as non-soy protein (32).

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 (33).

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.

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

• Drain a block of extra firm tofu, then pat it dry. Cut into cubes, season, and roast in the oven for a quick snack, salad topper, or stir fry ingredient.
• Crumble a block of extra firm tofu and cook it on the stove with veggies for a vegan scrambled egg substitute.
• Slice a block of extra firm tube and grill or fry it to use in sandwiches.
• Add a slice of silken tofu to smoothies for additional protein.
• Crumble a block of tempeh for crockpot chilis, stews, or plant-based sloppy joes.
• Use prepackaged tempeh “bacon” to make a plant-based BLT.
• Cook edamame and season with salt for a side dish.
• Add miso to soups or homemade salad dressings.
• Replace dairy milk with fortified soy milk in baked goods, soups, smoothies, sauces, and breakfast cereals.
• Add a scoop of soy protein powder to your pre- or post-workout smoothies.

Summary

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

Soy is a good source of protein, fiber, and an array of important vitamins and minerals. 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.

In fact, 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.