Is Soy Protein Good or Bad for You

by Vanya Sharma last updated -

Soy protein is one of the most commonly found ingredients in various food products. Turn over a nutrition bar or a box of veggie burgers, and you’ll find soy protein isolate (SPI) featured prominently on the ingredient list. However, there have been many debates surrounding the benefits and risks associated with the consumption of soy protein. Here in this article, we discuss its nutrition, benefits, and side effects.

What is Soy Protein?

Soy protein is a protein isolate derived from soybeans. It is made by dehulling and defatting a soybean meal. Soy protein serves as a good source of nutrition for vegetarians, vegans, people with a habitually-conscious lifestyle, and those who simply want to avoid dairy products. While many people praise soy protein isolate powder for its benefits, there are those who consider it as a somewhat controversial food. In a study published in 1995, quoted in the Journal of Perinatal Education in 2003, it estimated that over 12000 food products contained soy protein, including soy milk, miso, tempeh, tofu, different meat alternatives, meal replacement shakes and protein shakes, and various cereals. [1]

A closeup view of soybeans with wooden spoon and sac

Soybeans are the most popular type of legume. Photo Credit: Shutterstock


As the name suggests, soy protein isolate is rich in protein, with a 100-gram serving containing 88.3 grams of protein. It is also rich in several minerals such as calcium, iron, phosphorus, magnesium, sodium, potassium, and zinc as per the USDA Nutrient Database. Soy protein contains various vitamins including folate, vitamin B-6, niacin, riboflavin, and thiamin. [2]

What makes it even healthier is the fact that it contains zero sugars and carbohydrates. At the same time, this protein provides a good supply of water and energy to the body.

Is Soy Protein Good or Bad for You?

Now coming to the answer of whether soy protein is good or bad for you – studies reveal that soy protein isolate is beneficial for heart health, obesity, pregnancy, cancer, and more. We have discussed the health benefits of soy protein in detail below. [3]

Good for Pregnant Women

According to a study published in the Journal of Perinatal Education, soy protein is a good source of vitamin D. The study also says that fortified milk and fortified soymilk are the only trustworthy dietary sources of this vitamin, as other dairy products contain little to no vitamin D. So, for women who are sensitive to the sun or do not get as much sun as they like, soymilk serves as a great dietary supplement. [4]

Anticancer Potential

A study published in the Journal of Carcinogenesis reveals that soy protein isolates help inhibit the growth of aberrant crypt foci, which are the supposed precursors to colon cancer. In this study, pregnant and lactating rats were put on a soy protein diet and the results showed a long term anti-carcinogenic effect on them. [5]

Another study published in 2017, in the journal Medicines, [6] suggests that soy isoflavones may help better the prognosis of breast cancer. Having said that, the research does show conclusive evidence for the prevention of breast cancer in those whose dietary soy intake is high during their early years. [7]

Promotes Heart Health

The American Heart Association conducted a randomized controlled trial in 2008 and observed that isolated soy protein may help decrease LDL (bad) cholesterol in the body, but has no effect on HDL (good) cholesterol, lipoprotein or blood pressure. [8]

There are studies that suggest that Asian populations consuming soy as a dietary staple have a lower risk of heart diseases than those who rely on a typical Western diet. A decrease of 9.3 percent was seen in the total serum cholesterol levels, 12.9 percent in the LDL cholesterol levels, and 10.5 percent in triglycerides, as per a study published in the journal Circulation. These cholesterol-reducing effects of soy protein make it good for heart health. [9] [10]

Reduces the Risk of Obesity & Diabetes

Soy protein helps to control hyperglycemia, hyperlipidemia, hyperinsulinemia, and body weight, as per a study published in the American Journal of Clinical Nutrition [11]. These unique benefits of soy protein help both diabetics and nondiabetics in the regulation and control of blood sugar and obesity.

Promotes Bone Health Postmenopause

Soy protein is linked to the prevention of bone mineral density in postmenopausal women as per a study published in the Journal of Clinical Endocrinology and Metabolism. The report also suggests that it may slow down or reduce the onset of osteoporosis in peri- and postmenopausal women. [12]

Promotes Muscle Build-up

Soy is a complete protein, which means it contains all the amino that your body needs from food and cannot make on its own, as per a study published in 2014. While soy may not be a better source of protein than whey, studies reveal that it is better than casein. The study suggests that soy proteins work best when combined with other sources of protein. There are also research studies that suggest soy protein may give even better results when combined with dairy, thereby helping improve muscle health. [13] [14]

Side Effects & Controversies

There are many speculations about soy protein – of it being good or bad for health. We have already looked at how it can be good for health, now let’s take a look at its potential side effects.

  • Phytates: Research published in the Journal of Agriculture and Food Chemistry reveals that soy protein contains antinutrients, called phytates, which lower the iron and zinc content in it. However, phytates alone do not lead to any adverse effects on your health unless you solely rely on soy protein as a source of iron and zinc. It is suggested to have a balanced and wholesome diet, one that supplies your body with the optimum nutrition it requires. [15]
  • Thyroid Function: There are studies that suggest soy protein may affect the thyroid function in your body. The presence of isoflavones in soy interfere with the thyroid function and the production of hormones. However, there is more research required on this, as contrary to that, there are also studies which suggest that soy has little to no effect on the thyroid function. [16] [17] [18]
  • Hormones: There are also those who simply steer clear of this protein as it contains phytoestrogen, which may affect the hormone levels in their body as per an NIH report published in 2014. It is also rumored to reduce the testosterone levels in men, although research suggests that soy has no relevance with regards to this. [19] [20]

Soy products are often deemed controversial because they are sometimes genetically modified (GMO). However, there is no research that currently supports the idea that eating GMO soybeans can have adverse effects on health. More research on this is still required. Protection Status
About the Author

Vanya Sharma is a writer at heart with interests in the health and nutrition domain and has experience in content creation, collaboration, and content strategy. Vanya has completed the “Introduction to Food and Health” certificate program from Stanford University, US. She aims to bring unbiased and helpful information to all those seeking to make their health and lifestyle a priority.

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