Written by Ben Carlisle
Last updated on: Sep 18, 2022
Kimura Athletic may earn a small commission through our links. Learn more.
Whether soy or pea protein is better will depend upon an individual's personal goals. Both of these proteins are ideal for those following vegan diets or wanting to reduce the amount of animal protein they consume. Pea and soy protein are amongst the leading plant proteins.
Both soy and pea are great sources of protein with a complete amino acid profile. Amino acids are the building blocks of protein and help the body grow and function. After you consume protein, your body breaks it down into amino acids. Your body cannot make the nine essential amino acids, so they must via food sources (1).
The added nutrients within soy and pea protein powders, determine which protein powder is best for an individual. Nutritionally, soy protein is rich in plant fats and fibre. Whilst, pea protein powder is rich in iron, and contains good levels of the branched chain amino acids leucine, isoleucine and valine. The 3 amino acids are known for their role in muscle protein synthesis. Pea protein isolate is used in pea protein powder, which results in it being low in lectins. Soy protein isolate contains no lectins.
Soy protein powder is made from defatted soybean flakes. These flakes are washed in water or alcohol. This process removes the sugar and dietary fibre stored within them. Next, they are dehydrated, then made into a powder. As soy protein is lactose-free which is a common allergen, it is used to make infant soy milk. This is an alternative milk for babies with allergies. Soy is also frequently used for alternative dairy foods.
Pea protein isolate powder is made from yellow peas. The protein is isolated from the peas to give pea protein isolate. This is done by drying out the peas and mechanically removing the outer shell. Then the pea is milled down into a flour. This flour consists of protein, starch and fibre. The next step is to isolate the protein from this flour. As it is water soluble wet filtration and centrifugation is used.
Then the protein is precipitated to its isoelectric point. This dry spray is solubilised given a beige white powder. This beige white powder is pea isolate and will be typically 75g of high quality protein per 100g of powder. Similarly, to soy, pea protein is lactose-free making it a great option for those who are sensitive to dairy products.
Protein is important as it is used by the body to restore cells, grow muscle tissue, skin, bones, organs, hair and nails (2). It is recommended to take 7 grams of protein for every 20 pounds (9.07 kg) of bodyweight (3). For example, someone who weighs 200 pounds (90.72 kg) you will need to consume 70 grams of protein daily.
Amino acids are often referred to as the building blocks of protein, this is because they help your body to grow and function. When you consume protein, your body breaks it down into amino acids (1). There are over 20 amino acids in the human body and nine of them are classified as essential. Here the word essential means, you have to get them through a food source or a supplement. The food sources which typically contain all of the essential amino acids are animal proteins such as red meats, poultry, and dairy (3). Of the 9 essential amino acids 3 are known as the branched chain amino acids. These are; leucine, isoleucine and valine.
Often plant-based proteins do not have an amino acid composition with good levels of all nine essential amino acids. This is also true of plant based protein powders. For this reason it is important to know the nutritional content of any vegan protein powders you are thinking of taking, so you can tailor your diet accordingly.
Recent studies have found even the most balanced vegan diets can lack the daily recommend intake of protein. This has meant the market for vegan protein powders has grown, to help ensure vegans get enough protein.
Like whey protein, vegan protein powders are most often consumed as shakes pre or post workout. However they can also be added into meals and snacks. Examples include pancakes, muffins, porridge oats and yoghurts.
Unlike many other plant-based protein powders, soy does have a complete amino acid profile. Similarly, pea protein also contains all the essential amino acids, but its methionine levels are low (4). These low methionine levels have resulted in divided opinions as to whether pea protein can be referred to as a complete protein. For this reason some of the best pea protein powder supplements are blends to give good methionine levels.
A study into the percentage of protein content within a range of pea and soy protein powder manufacturers showed pea generally contained more protein. Soy products had protein contents which ranged from 61 to 91% and pea ranged from 77 to 81% (5).
The range of protein content in the soy proteins was very wide. The range of protein in pea protein powders was much closer. As to which plant protein wins in the pea protein vs soy protein debate. The answer is it depends upon the protein supplement in question. Pea protein shows a consistently high protein content across supplements. This means with pea protein you can be more certain you are getting a high quality protein powder regardless of brand. Whereas with soy you need to be careful to make sure you are getting a quality plant protein. If you do want a soy supplement it is recommended to read the nutritional information carefully and to choose a powder which is derived from soy protein isolate.
It is a common question for those on a plant based diet as to which of pea and soy protein powders best supports muscle growth. As mentioned previously soy protein is a complete protein, whilst there is still a debate over whether pea protein should be classified as a complete protein. However, it must be noted pea protein does contain higher concentration of amino acids than soy protein powder.
New research into the qualities of soy protein powder suggest it is not able to support muscle protein synthesis (MPS) in the same way whey protein does (6). Whereas studies into the effect pea protein has on muscle thickness and strength have shown pea protein powder to be as effective a supplement as whey protein (7). This may be because it has the required branched chain amino acids (BCAA's) which support muscle growth (8).
Consuming soy protein powder not only helps increase protein intake, but also provides a good source of plant fats and fibre. Additionally, it is rich in B vitamins, potassium and magnesium (9). Research into the nutrients within soybeans showed, all soybean varieties accumulate polyphenols (10). Polyphenols is a type of antioxidant which could help you body with cell damage and serious conditions such as heart disease (11). There is also evidence to suggest soy protein powder can also aid those trying to lose weight (12).
Further research implies populations with diets rich in soy protein and low in animal protein also have lower risk of developing prostate and breast cancer (13). Finally, there are studies which have shown soy protein powder is the only protein powder (including animal-based proteins) which has a score of 100 for digestibility (14).
Pea protein powder is hypo-allergenic. It is free from the 8 main allergens, one of which is soy. It has a complete amino acid profile. And is high in arginine, which helps with blood flow and heart health. It also contains good levels of the essential amino acids’ leucine, isoleucine and valine which play critical roles in the regulation of energy homeostasis, metabolism, gut health, immunity and disease (15).
Further to this it is a good source of iron making it a quick and effective way to top up iron levels each day. For those looking to reduce their weight, pea protein powder can be a great way to do this. Additionally its mix of fibre resistant starch components help to suppress appetite and glycemia (3).
Pea protein has been found to be more effective than all protein powders aside from casein protein when it comes to suppressing appetite when used as a pre-load. This effect of making individuals consume less calorie after taking pea protein has lead to many using pea protein for weight loss goals.
Whilst there are many benefits of both pea and soy protein the are some potential side effects. Despite soy being lactose free, it is unfortunately one of the 8 common allergens. This makes it unsuitable for a number of people. Additionally, there is currently an ongoing debate about whether soy is a good alternative to diary for the vegan community due to the effect soy can have on the body.
Soy is a unique plant-based product, because it contains a high concentration of isoflavones, a type of plant estrogen. Soy isoflavones can bind to estrogen receptors in the body and cause either weak estrogenic or anti-estrogenic activity (9).
With regards to pea protein, there is currently a lot of discussion around whether pea protein can be classified as offering a complete protein due to its lower levels of methionine. In reality, this should not be a problem as a pea protein powder can easily be combined with a plant based food high in methionine to make sure all essential amino acids requirements are met. Also, pea protein is normally, slightly higher in calories per serving when compared to soy protein powder.
Pea protein and soy protein powder both have benefits. Both plant proteins have good digestibility. With soy being slightly ahead of pea for digestibility. They are also both plant-based products, which makes them vegan friendly protein powders.
Both powers offer a good protein content. With pea showing a more consistently high protein content when analysed across a range of supplements. However, some soy protein isolate supplements do have a higher protein content than pea supplements. To make sure you get the protein content per serving you need it is important to read the labelling of any supplement you purchase.
If you are taking a protein powder to enhance your muscle mass gain, pea protein offers more amino acids per serving and studies have shown it is the best plant-based alternative for muscle repair and growth (8). Pea protein is also hypoallergenic whereas soy is 1 of 8 most common allergens.
When deciding which is better out of pea and soy protein it is important to analyse all the facts and your own personal needs before deciding which plant based supplement to go with. However, in most cases pea protein will provide you with most benefits, especially if you choose one of the leading pea protein supplements.