Soy Protein Isolate: How It Works, Benefits, Clinical Studies And Side Effects

Soy Protein Isolate

What is Soy Protein Isolate?

Soy Protein Isolate

It is a protein powder isolated from soybeans which is almost fat-free as it contains about 95% protein.

Function: It is used in the food and beverage industry and also as a dietary supplement for muscle building and weight loss.

Soy refers to soybeans which can be processed into soy milk – a beverage which may contain fortified calcium from soybeans, soy protein – a protein powder or soy fiber – made from the fibrous portion of the soybeans. Soy protein isolate commonly occurs in a dry powder form and is isolated from the other components of soybeans. It is about 95 percent protein, making it almost fat- and carb-free. Most commonly, soy protein isolate is available in the market as either plain or flavored shake powder.

Benefits of Soy Protein Isolate for Muscle Growth

Soy protein has the following benefits for body builders:

  • Performance enhancement
  • Increased muscle mass
  • Decreased fat mass
  • Increase in muscle strength
  • Increased muscle growth
  • Preventing muscle loss

How Does It Work?

Soy protein contains isoflavones which are classified as phytoestrogens or commonly called as plant estrogens. There has been some misconception about soy protein decreasing testosterone levels in men and promoting feminine characteristics but according to a meta-analysis ( of different research publications, it has been found that soy protein does not decrease testosterone levels.

Growth Hormone

It has been found is that soy protein increases the levels of growth hormone (GH) in the body. Soy protein contains the amino acids lysine and arginine which are known stimulate the release of GH. GH increases muscle growth and strength leading to enhanced performance of athletes and body builders alike.

Read More: Whey Protein Concentrate: How It Works, Benefits, Clinical Studies And Side Effects

Other Benefits

benefits of having soy protein in your diet

There are many uses and benefits of soy protein as follows:

  • Serves as a fat-free source of nutrients as it contains less than 1% of fat
  • It may lower blood cholesterol
  • It makes blood vessels more flexible
  • It can help in reducing high LDL cholesterol
  • May help in removing menopausal symptoms and PMS (Premenstrual Syndrome)
  • It’s abundantly used in the food and beverage industry for making different products such as fruity drinks, sauces and soups, fortified milk powders, beverage powders, boxed meals, infant formulas, power bars, cereals and cornflakes, bakery items such as bread, cakes and pastries, soy meat, etc.
  • It serves as a complete vegetable protein as it contains the amino acids which are essential for growth. The amino acid content is similar to that in eggs, milk and meat.
  • It may help in preventing osteoporosis
  • It may help in the prevention of some cancers
  • It slows the progression of kidney disease
  • It is also used as a treatment for digestive disorders such as diarrhea and constipation
  • It can treat muscle stones caused by intense exercise
  • It helps in weight loss

Clinical Studies

clinical studies on soy protein

In a study ( conducted on eight women, it was found that soy protein increased the levels of GH in the body. The participants were given complete soy protein, hydrolyzed soy protein, an amino acid combo or a placebo.

Side Effects

Using soy protein as a medication or supplement is possibly safe. But some people may experience the following mild side effects:

  • Nausea
  • Vomiting
  • Bloating
  • Constipation
  • Allergic reactions that cause itching and rashes

A word of caution

Even though soy protein is quite safe to use for healthy individuals, people with certain health complications need to be cautious while starting with soy protein supplements:

  • High medicinal doses of soy protein must be avoided during pregnancy and breast-feeding as it may interfere with the development of the baby
  • Make absolute sure that you don’t have any soy allergies before starting on your soy protein supplements
  • Children with cystic fibrosis should steer clear of soy as it can interfere in protein processing
  • There is conflicting evidence of soy for breast cancer; some supports the role of soy protein in prevention while some research suggests that it can feed the cancer cells leading to cancer growth
  • It might worsen hypothyroidism
  • Diabetics taking medication for regulation of blood sugar are under the risk of plummeting blood sugar levels
  • People with asthma, hay fever and milk allergies should avoid using soy because it might trigger certain allergic reactions


There has been a lot of conflict regarding the role of soy protein in changing the testosterone levels in men. It has been established through research that soy protein does not reduce testosterone levels, but rather increases the levels of growth hormone in the body. The growth hormone is responsible for increasing lean muscle mass and enhancing performance. If you do not have any medical conditions then you can safely use soy protein isolate for supplementing your muscle training. Just make sure to have a word with your doctor before you start on soy protein so as to avoid any health complications that might occur.