Is soy good for you?

What is soy?

The soybean is a complete protein and a species of legume native to East Asia. What’s more, it contains all nine essential amino acids, making soy an important source of protein for many people, especially those who follow a plant-based diet.

Varieties of soybeans include:

• Green soybeans: Often referred to as edamame, people steam and eat them out of the pod as an appetiser. They are also widely used in salads, stir-fries, and soups.
• Yellow soybeans: Typically used to make soy milk, tofu, tempeh, and tamari. They can also be used to produce soy flour, which is functional in baking.
• Black soybeans: Various Asian food cultures use fermented or simmer black soybeans in traditional dishes such as kuromame.

In general, the less processed a food is, the more vitamins, minerals, and beneficial compounds it may contain. Alternatively, the more processed a food is, the more salt, sugar, fat, and unnecessary additives it likely contains.

As a result, minimally processed soy foods, including, tofu, tempeh, edamame, and unsweetened soy milks, are considered healthier than soy-based protein powder, mock meat, energy bars, or sweetened soy milks.

In addition, fermented soy foods, including soy sauce, tempeh and miso, are often considered healthier than non-fermented soy products. In short, fermentation helps reduce some of the anti nutrients naturally found in foods containing soy.(1)

Soy-based foods are often at the heart of a plant-based diet, which more and more people are adopting for the benefit of their health and the environment. Subsequently, they are now widely accessible in almost every supermarket and are no longer just exclusive to quirky health-food stores. However, there is a lot of contradictory and confusing information regarding soy. Therefore, this article will review the latest scientific evidence to determine whether soy is good for you.

Nutritional content of soy

Soybeans are protein-rich and contain all of the essential amino acids that the human body needs. In addition, they are one of the few known plant foods (other than amaranth seed and to a lesser degree, quinoa) to contain all the essential amino acids, like those found in meat.

Moreover, soybeans are rich in fatty acids, fibre, vitamins and minerals. In addition to their vitamin and mineral content, soybeans are a natural source of polyphenols, an antioxidant that may help protect the body against cell damage and conditions such as heart disease.

Soy is especially rich in isoflavones, a polyphenol known as phytoestrogen due to its ability to attach to and activate estrogen receptors in the body. Soy isoflavones are one of the main reasons behind the many proposed health benefits of soy-based foods. Furthermore, depending on the variant, boiled soybeans can contain 90–134 mg of isoflavones per 100g.

100g of cooked soybeans contains:(2)

• Kcal: 141
• Protein: 12g
• Fat: 6g
• Carbohydrate: 11g
• Fibre: 4g

However, the nutritional content of other soy products may vary based on how manufacturers have processed them and which ingredients they have added.

Cholesterol

Cholesterol is a fatty substance carried through your blood, attached to proteins. Your body needs cholesterol to build healthy cells. However, too much of it can cause serious health problems. Lipoproteins are a combination of proteins and cholesterol. In addition, there are different types of cholesterol, based on what the lipoprotein carries:

• Low-density lipoprotein (LDL): "Bad" cholesterol, transports cholesterol particles throughout your body. LDL cholesterol builds up in the walls of your arteries, making them hard and narrow.
• High-density lipoprotein (HDL): "Good" cholesterol, picks up excess cholesterol and takes it back to your liver.

Research suggests that soy may help lower LDL cholesterol levels and increase HDL cholesterol levels. An analysis of clinical trials indicates 14-50g of soy protein can significantly reduce LDL cholesterol levels in the arteries, while moderately increasing HDL (good) cholesterol levels. What’s more, whole soy products have a greater effect on improving cholesterol levels than processed soy products. This could be due to phytoestrogens or soy proteins working alone or together. Other factors include its high-fibre and low saturated-fat content. Interestingly, people with existing risk factors for heart disease, such as high cholesterol levels, had more significant decreases in LDL cholesterol than people with optimum cholesterol levels.(3)

A study also found individuals who include at least 25g of soy protein daily in a diet low in saturated fat and cholesterol can reduce LDL cholesterol levels by about 3%. However, this could be because of a reduction in the amount of animal protein in the diet. Swapping out animal-based foods for plant foods like soy decreases saturated fat intake and increases fibre intake, which may indirectly improve our blood cholesterol levels. Although, more data needs to be available to form a definitive answer.(4)

Heart disease

Heart disease is a broad term that covers many heart-related problems and conditions, from an abnormal heartbeat and birth defects to a buildup of plaque in the arteries.

Research shows a link between soy intake and total cholesterol and LDL cholesterol levels, both known risk factors of heart disease. Diets rich in legumes, such as soybeans, have a biological plausibility to lower the risk of heart disease.(5)

This could be due to isoflavones. They help reduce inflammation in blood vessels and improve their elasticity, two factors thought to protect heart health.(6)

In addition, a recent review further links soy-rich diets to a 16% lower risk of stroke and heart disease.(7) However, despite biological plausibility, more research is needed to address confounding factors.

Seek emergency medical care if you have the following symptoms of heart disease:

• Chest pain
• Shortness of breath
• Fainting

Heart disease is easier to treat when detected early. Talk to your doctor if you have any concerns about your heart health. This is especially important if you have a family history of heart disease. If you think you suffer from symptoms of heart disease, make an appointment to see your doctor.

Related readings

• Is dairy good for you?
• Is a low fat diet healthy?