Whey and soya proteins and the effects of training
Just a few decades ago, whey was regarded mainly as a by-product of cheese production. Advances in filtration technology have made it possible to extract a highly concentrated source of protein from it, with a beneficial amino acid profile. At the same time, soya protein, one of the most thoroughly researched plant-based sources of protein, gained popularity. Today, both are frequently used by those who do strength training, although their composition and the body’s response to their consumption are not identical.
Whey protein and soya protein – similarities and differences Protein in the diet and strength training Whey and soya protein during strength training – findings from published studies
Whey protein and soya protein – similarities and differences
Whey protein is derived from milk and forms part of the proteins remaining in the liquid whey after the curd has been separated during cheese production. In supplements, it is most commonly found as a concentrate or isolate. An isolate usually contains a higher proportion of protein and less fat and lactose than a concentrate. Whey protein provides all the essential amino acids, i.e. those that the body cannot produce in sufficient quantities on its own. It also contains a relatively high amount of leucine, one of the amino acids involved in regulating muscle protein synthesis.
Soya protein is obtained from soya beans. It is also available as a concentrate and an isolate, with the isolate having a higher protein content. It is a complete plant-based protein, as it provides all the essential amino acids. However, its amino acid profile differs from that of whey protein. Among other things, soya protein has a lower content of methionine and leucine.
Protein in the diet and strength training
Resistance training brings about changes in muscle protein metabolism, and the supply of amino acids enables them to be used to build new proteins. Essential amino acids, which the body must obtain from the diet, are of particular importance. Leucine is one of the key amino acids, as it plays a role in triggering the processes involved in muscle protein synthesis, and its content is one of the indicators distinguishing between different sources of protein.
Gains in muscle mass and strength depend primarily on a properly planned training programme, whilst the diet provides the energy and building blocks needed for tissue repair. In the European Union, permitted health claims for protein include, amongst others, that it contributes to the growth and maintenance of muscle mass, provided the product meets the criteria to be classified as a source of protein (i.e. at least 12 per cent of the product’s energy value comes from protein). Increasing protein intake may be of lesser importance if the amount in the diet is already sufficient.
Whey and soya protein during strength training – findings from published studies
On 26 December 2025, the "Journal of Dietary Supplements" published the results of a review of four databases; of the 1,813 publications identified, 12 studies involving a total of 261 participants were included in the subsequent meta-analysis. The study included healthy adults aged 18–30, comprising both those with prior training experience and those without. Participants undertook resistance training and consumed either whey or soya protein concentrate or isolate. The primary measures assessed were lean body mass, as well as strength in the bench press and squat, and the concentration of essential amino acids in the blood.
In the studies involving whey protein, a greater improvement in strength was observed compared with the control groups. For the bench press, the mean difference was 8.87, and the range within which the true effect was highly likely to fall was from 5.95 to 11.79. For the squat, the mean difference was 9.60, with a range of 5.61 to 13.60. The results of the individual studies were relatively consistent. The authors also assessed the concentration of essential amino acids in the blood following protein intake and observed an increase in their peak concentration.
The interpretation of these results is limited by the small number of available publications and participants, as well as differences between the protocols used. The analysis included both previously trained individuals and beginners, whose response to starting strength training may vary.
Sources:
Davis, B. E., Young, I., Giglotti, J. C., Yao, J., & Tou, J. C. (2026). The Impact of Whey and Soy Protein Supplementation on Resistance Training in Young Adults: A Systematic Review and Meta-Analysis. Journal of dietary supplements, 23(1), 150–174. https://doi.org/10.1080/19390211.2025.2604679 Morton, R. W., Murphy, K. T., McKellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., Aragon, A. A., Devries, M. C., Banfield, L., Krieger, J. W., & Phillips, S. M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British journal of sports medicine, 52(6), 376–384. https://doi.org/10.1136/bjsports-2017-097608 Candow, D. G., Burke, N. C., Smith-Palmer, T., & Burke, D. G. (2006). Effect of whey and soy protein supplementation combined with resistance training in young adults. International journal of sport nutrition and exercise metabolism, 16(3), 233–244. https://doi.org/10.1123/ijsnem.16.3.233
ADDED:
15/10/2026
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