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Soy vs Whey Protein Powder: Which is Best for You?

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

Protein Content

As shown in the table below, soy protein supplements usually have at least as much protein as whey protein powder. 

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

SupplementCaloriesProteinCarbs FatsRating
Bodybuilding Warehouse Whey Concentrate (Amazon)375764.75.74.3/5
Myprotein Whey Concentrate (Amazon)411806.27.34.4/5
Optimum Nutrition Whey Concentrate (Amazon)378795.64.24.7/5
Bodybuilding Warehouse Whey Isolate (Amazon)37490113.6/5
Myprotein Whey Isolate (Amazon)359814.61.14.2/5
Optimum Nutrition Whey Isolate (Amazon)366834.51.44.5/5
Bodybuilding Warehouse Soy Isolate (Amazon)36884614.1/5
Myprotein Soy Protein (Amazon)360901.81.53.9/5

While an article by Harvard Health suggests the general population only requires 0.8 grams of protein per kilo of body weight per day, a meta-analysis in the British Journal of Sports Medicine (Morton et al., 2018) indicates that those undertaking resistance training should aim for 1.6 grams to repair their muscle tissue. 

For example, an 80-kilo individual would require 128 grams to meet their daily protein requirements. Since whey and soy protein supplements can contain up to 27 grams of protein per 30-gram scoop, five scoops of either each day would provide enough protein to hit this target (5 x 27 = 135). 

Of course, you wouldn't need this many scoops if you're also consuming high-protein foods. 

Essential Amino Acids

One reason whey protein powder is often called the "gold standard" is its complete amino acid profile. However, as shown in the graph below, soy protein powder is also a complete protein source as it has all of the essential amino acids. 

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

A graph showing amino acid concentrations in soy and whey protein powders

A potential shortcoming of soy protein supplementation is the lower levels of leucine, an amino acid that has a strong effect on muscle protein synthesis (Garlick, 2005). However, having just a few grams of leucine on a daily basis can lead to significant increases in power and endurance (Crowe et al., 2006). As soy protein isolate has 7 grams of leucine per 100 grams, just a couple of 30-gram scoops daily would provide enough leucine for you to enjoy these benefits ([2 x 0.30] x 7 = 4.2 grams).

If you're interested in the amino acid profiles of other plant-based proteins, check out my articles comparing pea protein and soy protein and pea protein and brown rice protein. 

Muscle Growth

One randomised controlled trial (RCT) showed that when combined with resistance training both whey and soy protein supplements comparably enhanced muscle mass compared to a placebo (Candow et al., 2006).

If the idea of drinking lots of protein shakes to increase your protein intake doesn't excite you, check out my article on the best protein bars. Those interested in building muscle mass could also look at my article on EAAs and BCAAs, which come in both pill and powder form. 

Muscle Strength

The aforementioned RCT also found that, over a 6-week training programme, soy and whey protein powders promoted similar increases in strength (Candow et al., 2006). 

If you struggle to increase your strength and size, you might want to read my article on the best protein supplements for weight gain. 

Muscle Recovery

A study published in the Journal of the International Society of Sports Nutrition found that whey and soy protein supplements equally reduced performance decline during speed and endurance training. Additionally, both supplements were similarly effective in promoting recovery from muscle damage (Kritikos et al., 2021).

Athletic Performance

Systematic reviews of RCTs indicate that soy and whey supplementation can reduce perceived exertion and enhance endurance, aerobic power, and isometric muscle strength in female and male athletes (Lam et al., 2019; Zare et al., 2023).

As well as by increasing the amount of protein you consume, you can increase athletic performance through other supplements that tend to be suitable for those on a plant-based diet, such as BCAAs and creatine (levels of which are often low in those who don't eat meat; Kaviani et al., 2020). 

Weight Loss

Although numerous studies indicate that plant-based proteins and whey proteins have comparable effects, whey protein may offer a slight edge in weight loss. Research comparing whey protein to soy protein in overweight and obese individuals revealed that whey protein was more effective for fat loss (Piri Damaghi et al., 2022). 

If you're interested in developing lean body mass, you might like my article on the best protein supplements for weight loss. 

Other Frequently Asked Questions

Does Soy Protein Reduce Testosterone Levels?

While some small studies suggest that testosterone levels may be higher in those taking whey protein compared to soy protein (Kraemer et al., 2013), one meta-analysis of many studies found no effect of soy consumption on sex hormones (e.g., testosterone) in men (Hamilton-Reeves et al., 2009). 

Can Protein Supplements Cause Allergic Reactions?

Soy allergy affects around 0.4% of young children, with about 50% outgrowing it by age 7 (Savage et al., 2010). Symptoms can include gastrointestinal issues like vomiting, diarrhoea, and abdominal pain, skin reactions such as hives and eczema, and respiratory problems like wheezing and nasal congestion. If you're concerned about soy allergies, you might want to check out my articles on alternative plant proteins:

As whey supplements (e.g., whey protein concentrate) come from cow's milk, they're not suitable for those who need to avoid dairy products because of lactose intolerance. If you'd like to avoid milk products for this reason, you might like to learn more about plant-based protein powders by reading one of the following articles:

Plant-based proteins are also covered in my article on vanilla and chocolate protein powders. 

Can Soy Affect the Immune System?

One of the potential health benefits of consuming soy is improved overall immune function. Soy contains isoflavones like genistein, daidzein, and glycitein, which are phytoestrogens capable of binding to estrogen receptors (Masilamani et al., 2012). Since estrogen binding to these receptors is crucial for immune responses (Khan & Ahmed, 2016), the phytoestrogens in soy may also enhance immunity.

Final Words on Soy and Whey Protein Supplementation

If you follow a vegan diet and need to avoid animal-based protein, soy protein supplements could be a great choice. 

While there's a mountain of evidence that whey can help with a wide range of fitness goals, studies also indicate that there tend not to be significant differences between whey and soy dietary supplements in the extent to which they can support muscle building (Candow et al., 2006), strength (Candow et al., 2006), or recovery (Kritikos et al., 2021). For lean muscle mass and reducing body fat, however, whey may have a slight edge (Piri Damaghi et al., 2022). 

You might also be interested in my articles on the best supplements for recovery, how rice powder compares to whey powder, how whey compares to casein protein, how whey compares to collagen protein, how whey compares to essential amino acid supplements, how whey compares to BCAAs, how whey compares to creatine, how whey compares to mass gainer, how whey compares to eggs, the best protein supplements for diabetics, and the best protein supplements for seniors.

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. 

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Footnotes

*Macros, calories, and ratings can vary across flavours and as new versions are released. 

References