Soy Protein Concentrate vs Isolate: Which is Best?

UK Fitness Pro
UK Fitness Pro
· 7 min read
A packet for soy protein isolate

Soy proteins are as good as whey proteins for building lean muscle mass. 

As well as examining the evidence for this, we explore how soy compares to whey in terms of essential amino acids and protein content and look at some of the key health benefits of soy.

But first, what are the main differences between soy protein concentrate and isolate?

Soy Protein Concentrate vs Isolate: The Main Difference

Soy protein isolate and soy protein concentrate differ primarily in their protein content and processing methods (van den Berg et al., 2022). 

Soy protein isolate, derived from whole soybeans, undergoes additional processing to remove excess water and soluble carbohydrates, resulting in a higher protein content and a more pure protein form. In contrast, soy protein concentrate is made from defatted soy flour with less processing, retaining more of the original nutrients but containing less protein. 

Isolate powder is the better option for those seeking maximum protein intake, while soy protein concentrate might be suitable for those who prefer a more natural product with a broader nutrient profile.

Essential Amino Acids in Soybean Protein

Soybeans contain all essential amino acids, making them a complete protein source (Gorissen et al., 2018). 

Grams of Essential Amino Acids per 100 Grams of Soy Protein Isolate and Whey Protein Isolate

As shown in the graph above, the levels of the essential amino acids in soy protein are similar to those seen in whey, which is often considered the "gold standard" among the various types of protein. Although whey has substantially more leucine, an amino acid that appears to be particularly important for muscle protein synthesis (Garlick, 2005), as little as 3.5 grams of leucine daily can significantly improve power and endurance (Crowe et al., 2006). From the figure, we can infer that about 50 grams of soy protein isolate would be needed to get 3.5 grams of leucine, which works out to less than two 30-gram scoops. 

If you're interested in how other plant proteins compare to whey in terms of their amino acids, check out my article on plant vs whey protein for bodybuilding. 

Do Soy Protein Products Have Enough Protein?

As shown in the table below, soy protein isolate tends to have at least as many grams of protein per 100 grams as whey protein concentrate and whey protein isolate. 

Calories and Macronutrients per 100 Grams of Soy and Whey Proteins from Bodybuilding Warehouse, Myprotein, Peak Supps, and Optimum Nutrition 

SupplementCaloriesProteinCarbsFatsRating
Bodybuilding Warehouse soy protein isolate3689061NA
Myprotein soy protein isolate360901.81.53.9/5
Peak Supps soy protein isolate (Amazon)381841.14.54.4/5
Bodybuilding Warehouse whey concentrate375804.75.7NA
Optimum Nutrition whey concentrate (Amazon)378795.64.24.7/7
Myprotein whey concentrate405778.37.14.6/5
Bodybuilding Warehouse whey isolate3749011NA
Myprotein whey isolate359814.61.14.6/5
Optimum Nutrition whey isolate (Amazon)366834.51.44.5/5

The Mayo Clinic suggests that those who lift weights should aim for a daily protein intake of 1.2–1.7 grams per kilo of body weight. For example, an 80-kilo individual would need 96–136 grams per day. As a scoop of soy protein isolate can contain up to 27 grams of protein, a few protein shakes daily would get you a long way towards your protein targets. 

If you follow a plant-based diet, you might also like my articles on soy and whey protein powders, whey, soy, and pea protein powders, and soy and pea protein powders. If you're not keen on chugging lots of protein shakes each day to recover from the muscle breakdown following a workout, you could explore increasing your protein intake with protein bars. 

Soy Protein Powder for Muscle Growth

A study in the International Journal of Sport Nutrition and Exercise Metabolism (Candow et al., 2006) had participants consume either whey protein, soy protein, or a placebo while following a 6-week training programme. The results revealed that both whey protein powder and soy protein powder led to notable improvements in muscle mass and strength compared to the placebo.

You can learn more about how protein supplements for those on vegan diets compare with whey protein in my articles comparing pea and whey protein and hemp and whey protein. 

Soy Protein Powder for Weight Loss

In a randomised controlled study (Deibert et al., 2004), 90 overweight and obese participants were split into three groups to examine the impact of different interventions on body composition: lifestyle education alone, a high-soy-protein, low-fat diet, and the same diet combined with guided physical activity. The findings demonstrated that both groups consuming soy protein, regardless of exercise inclusion, experienced significant fat loss compared to the lifestyle education group while maintaining lean body mass.

If you're interested in other plant-based protein proteins, you might like my articles on whey and rice proteins, hemp and pea protein powders, and brown rice and pea protein powders. Plant-based powders are also discussed in my article comparing chocolate and vanilla protein powders. 

Does Soy Have Positive or Negative Effects on Overall Health?

People often speculate about the potential positive or negative effects of certain foods and supplements. Here's what the scientific research says about how soy may impact your health...

Immune System Regulation

​One of the potential health benefits of soy consumption is the enhancement of overall immune function. Soy isoflavones, such as genistein, daidzein, and glycitein, are phytoestrogens, which can bind to estrogen receptors (Masilamani et al., 2012). As estrogen binding to estrogen receptors plays an essential role in immune responses (Khan & Ahmed, 2016), soy's phytoestrogen content might also promote immunity. 

Risk of Breast Cancer 

Research suggests that moderate soy consumption does not increase breast cancer recurrence risk in Western women and is associated with a better prognosis in Asian survivors. The protective effects may involve epigenetic changes influencing gene expression related to mammary cell fate and tumour biology, but more research is needed to fully understand these mechanisms (Hilakivi-Clarke et al., 2010).

Nutrient Absorption 

Phytic acid in soy can inhibit mineral absorption by binding with dietary minerals such as zinc, iron, and calcium, forming insoluble complexes. Despite this, moderate soy consumption is generally considered safe as the body can adapt to phytic acid over time, and the negative impact on mineral absorption is not significant if the overall diet is balanced and nutrient-rich. Additionally, phytic acid has potential health benefits due to its antioxidant properties and its role in reducing the risk of certain chronic diseases (Wang & Guo, 2021). 

Cholesterol Levels

A meta-analysis in the Journal of Nutrition revealed that soy protein (20–133 g/d) reduced low-density lipoprotein cholesterol (LDL-C) and suggested that having soy protein instead of animal proteins could reduce LDL-C by 3.6–6.0% (Jenkins et al., 2010). 

Soy Allergy

Soy allergy affects approximately 0.4% of young children, though 50% develop tolerance by age 7 (Savage et al., 2010). Symptoms of soy allergy can include gastrointestinal issues (e.g., vomiting, diarrhoea, abdominal pain), skin reactions (e.g., urticaria, eczema), and respiratory problems (e.g., wheezing, nasal congestion). If you suspect you're allergic to soy, you could consider alternative plant-based dietary supplements, such as pea protein, brown rice protein, or hemp protein. 

​Soy Products Besides Protein Powder

Soy Milk

Soy milk is often fortified with vitamins and minerals like B2, B12, D, calcium, and iodine. According to the BBC Good Food website, It offers several health benefits, including being a source of protective antioxidants, alleviating menopausal symptoms due to its phytoestrogen content, and supporting heart health due to its low saturated fat content.

Tofu

Among soy foods, Tofu may be the most well-known. As summarised on Healthline, it is rich in various vitamins and minerals, such as calcium, manganese, and iron, while low in calories and fat. Additionally, it contains beneficial isoflavones, which are linked to numerous health benefits, including reduced risk of heart disease and certain cancers and improved bone health.

Final Thoughts on Soy Protein

  • If you want to increase your protein intake while avoiding animal products or those made from cow's milk (e.g., if you have lactose intolerance), there's no reason you can't do so with plant-based foods like soy.
  • With their high-quality protein, low fat content, and balanced amino acid profile, soy protein powders can certainly assist you with strength and muscle building.
  • Like soy protein powders, food products made from soy (e.g., tofu) are defined by their high protein content and can be a great option for those interested in building muscle without the use of meat or dairy products.

About the Author

Dave Robinson, a co-founder of ukfitness.pro, has a background in psychology (BSc) and neuroscience (MSc, PhD). As well as strength training, he enjoys endurance challenges and has run ultramarathons, cycled across several countries, and completed the Three Peaks Challenge. When writing, he draws on scientific evidence to understand the pros and cons of different diets, supplements, and training regimes. 

References