Soy Protein vs Whey Protein: What to Choose and for Whom

Soy protein is cheaper than whey in many markets, suits vegans and has a complete amino acid composition. Whey, meanwhile, remains the most popular supplement in gyms. Instead of an abstract "which is better", our editorial team proposes to examine specific real-life situations and explain which protein is more appropriate for whom.

The short answer

If you consume dairy products and have no problems digesting them, whey protein will give a slightly larger anabolic return from each gram of protein. But if your diet is plant-based or milk does not suit you, soy protein is one of the best plant options with a complete amino acid composition.

For people who train several times a week and top up 1.6 g of protein per kilogram of body weight per day, the difference in results between the two proteins will be small. This is confirmed by meta-analyses, in particular the work of Messina and colleagues (2018).

The choice, therefore, is often determined not by biochemistry but by tolerance, taste, price and a person's values. And that is normal: the best protein is the one you will consume regularly and comfortably.

Below we examine the details that will help you make a conscious decision.

Scenarios: who chooses what

Vegan or vegetarian without dairy products - soy isolate or a blend of soy with other plant proteins. Soy has the best amino acid profile among popular plant proteins, so it is a logical basis.

Athlete without restrictions, goal - maximum muscle gain - whey protein. The advantage in leucine and in the speed of delivering amino acids to the muscles, shown in the study by Tang and colleagues (2009), makes it somewhat more effective at an equal dose.

Person with lactose intolerance - either whey isolate with minimal lactose content or soy protein. If even the isolate causes discomfort, soy becomes the first choice.

Person with a soy allergy - whey, obviously, if there is no allergy to milk as well. With an allergy to both products it is worth considering pea, rice or egg protein.

Servings and combining

For whey protein a typical serving is 20-30 g of protein. The study by Moore and colleagues (2009) showed that in young men about 20 g of quality protein after a workout almost maximally stimulate muscle protein synthesis.

For soy protein it is advisable to aim for the upper limit - 25-40 g of protein per intake - to compensate for the lower leucine content and the larger proportion of amino acids utilised in the liver.

An interesting option is combined products with whey, casein and soy. Such blends combine the rapid amino acid peak of whey with the longer action of the other fractions, although the advantages over plain whey in training studies are small.

Regardless of choice, distribute protein across 3-5 intakes throughout the day. The ISSN position (Jäger et al., 2017) emphasises that an even distribution helps to maintain a positive protein balance.

Special groups: women, people 60+, children and adolescents

Soy protein suits women just as well as men. Clinical studies do not link moderate consumption of soy protein with harm to women's hormonal health. However, in the case of hormone-dependent diseases or during treatment it is worth consulting a doctor.

For people over 60 who are fighting age-related muscle loss, whey is more suitable: its high leucine content helps to overcome the decline in the muscles' sensitivity to protein. But if they follow a plant-based diet, soy is acceptable, though with a larger serving.

As for children and adolescents, our editorial team believes that protein supplements are not a necessity for them. An ordinary varied diet usually fully covers the need for protein, and any supplements should be discussed with a paediatrician.

For pregnant and breastfeeding women, any protein powders should be introduced into the diet only after consulting a doctor, with attention to the composition, sweeteners and quality certificates.

Typical mistakes when choosing

The first mistake is refusing soy because of the testosterone myth. The meta-analyses of Hamilton-Reeves (2010) and Reed (2021) did not confirm an effect of soy protein on male reproductive hormones.

The second mistake is buying the cheapest soy concentrate instead of the isolate. The concentrate contains more oligosaccharides, which can cause bloating, and has a worse taste.

The third is assessing a product by the price of the tub rather than by the cost of pure protein. Often a more expensive pack turns out to be more advantageous per serving.

The fourth is ignoring independent analyses. For athletes undergoing doping control, product certification is especially important, as the IOC consensus warns (Maughan et al., 2018).

• Don't believe myths - check the meta-analyses.
• Choose the isolate if taste and digestion matter.
• Count the cost of 25 g of protein.
• Look for quality certificates.

Editorial conclusions

Whey protein is the optimal choice for people without restrictions who want maximum efficiency per gram, as well as for older people.

Soy protein is a full-fledged alternative for vegans, those allergic to milk and people with lactose intolerance, provided the serving is slightly larger.

In the long term, daily protein intake and the regularity of training matter more than the specific source.

We also recommend reading our articles on myths about soy, on protein for older people and on how to calculate the cost of a protein serving.

References

1. Messina M, Lynch H, Dickinson JM, Reed KE. No difference between the effects of supplementing with soy protein versus animal protein on gains in muscle mass and strength in response to resistance exercise. Int J Sport Nutr Exerc Metab. 2018;28(6):674–685.
2. Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA, Phillips SM. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol. 2009;107(3):987–992.
3. Moore DR, Robinson MJ, Fry JL, et al. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr. 2009;89(1):161–168.
4. Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
5. Hamilton-Reeves JM, Vazquez G, Duval SJ, et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 2010;94(3):997–1007.
6. Reed KE, Camargo J, Hamilton-Reeves J, Kurzer M, Messina M. Neither soy nor isoflavone intake affects male reproductive hormones: an expanded and updated meta-analysis of clinical studies. Reprod Toxicol. 2021;100:60–67.
7. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.