Could Yeast Replace Whey? What the Science Says About Single-Cell Protein

For years, the protein conversation has centered on mainly two categories: animal-derived proteins, led by whey, and plant-derived proteins, primarily pea, soy, and rice blends. A third category has been developing quietly in the background, and the early clinical data is worth paying attention to.

Single-cell protein (SCP), specifically yeast-derived protein isolate, is produced through precision fermentation rather than conventional agriculture. The organism at the center of this technology is Saccharomyces cerevisiae, the same strain of baker's and brewer's yeast that humans have used for at least 20,000 years. What is new is the process of refining it into a high-quality protein isolate with a nutritional profile that competes with conventional animal protein. I explored this in depth in a recent episode of my podcast, Thrive on Plants, in conversation with Walter Ross, founder and CEO of Spacemilk.

Nutritional Research

The most rigorous current standard for evaluating protein quality is the Digestible Indispensable Amino Acid Score (DIAAS), which accounts for both amino acid profile and true ileal digestibility. Whey protein scores approximately 109 by this measure. The ProteVin ingredient used in Spacemilk has a reported DIAAS of 121, though this figure is currently based on manufacturer data supplied by NextFerm Technologies and awaits independent, peer-reviewed replication. It should be interpreted with that context in mind.

What is well established is the clinical importance of leucine as the primary trigger for muscle protein synthesis. Leucine activates the mTORC1 signaling pathway, the central molecular switch for muscle repair and growth. Current evidence, including a 2021 systematic review in Frontiers in Nutrition (Wilkinson et al.) and a 2023 quantitative systematic review in Physiological Reports, supports a per-meal leucine dose of approximately 2.5 to 3 grams as a practical reference threshold in healthy adults, with older adults likely requiring toward the higher end of that range due to age-related anabolic resistance. 

The primary human trial data for yeast protein is encouraging. A 2024 double-blind, randomized controlled trial by Briskey and colleagues, published in the Journal of Food and Nutrition Research, enrolled 79 healthy men over age 40 who consumed either 40 grams of AnPro yeast protein or whey twice daily for eight weeks alongside supervised resistance training. Both groups achieved equivalent gains in total lean mass and trunk lean mass compared to a placebo. The yeast protein group additionally showed a significant reduction in diastolic blood pressure. It is worth noting that this trial was funded by Angel Yeast Company, the manufacturer of AnPro, which introduces potential for industry bias. The study population was male and over 40; data specific to perimenopausal or postmenopausal women does not yet exist for this ingredient. Emerging data also suggest a favorable effect of yeast-derived proteins on gut microbiome composition, though mechanistic data in humans remain preliminary.

Protein Purity

One of the more clinically relevant arguments for fermentation-derived protein concerns contamination risk. Soil-grown crops are bioaccumulators: during the protein isolation process, heavy metals, including lead, arsenic, and cadmium, can concentrate to measurable levels. Yeast protein produced in a closed-loop fermentation system bypasses the bioaccumulation pathway entirely. The organism grows in a controlled aqueous environment, not in soil subject to agricultural runoff, pesticide application, or atmospheric deposition. Third-party batch testing for heavy metals, pesticides, molds, and mycotoxins remains voluntary in the supplement industry and is not uniformly applied, which is worth understanding when evaluating any protein source.

Environmental Impact

Lifecycle analysis data from comparable yeast fermentation operations suggest approximately 40% less water and land use than soy protein production, and substantially less than beef. These figures are drawn from industry lifecycle analyses rather than fully independent, peer-reviewed studies, and should be presented as directional estimates rather than definitive data. What is well established in the literature is that fermentation-based protein production is structurally less land-intensive than field agriculture and is compatible with second-generation feedstocks, meaning substrates such as molasses that do not compete with the direct human food supply.

The Role of Supplementation

I could write an entire post on supplementation. Yeast protein isolate is not a replacement for a whole-food, plant-based nutritional foundation. Legumes, tofu, tempeh, edamame, and whole grains remain the evidence-based cornerstone of plant-predominant protein intake. A precision-fermented isolate is a supplementary tool for individuals who cannot reliably meet leucine thresholds or total protein requirements through diet alone. This gap is real and may become more common with age, particularly in perimenopause and post-menopause, and in patients with elevated requirements due to resistance training or metabolic conditions.

The evidence base for yeast protein is relatively early compared to whey, but I am excited. Decades of longitudinal data do not exist for this ingredient class. The existing evidence supports the conclusion that yeast protein is nutritionally complete, demonstrates clinical equivalence to whey for lean mass outcomes in a well-designed RCT, is low in allergenicity, and is structurally protected from the heavy-metal contamination documented in soil-grown alternatives. As fermentation technology scales and the research base matures, this category warrants continued clinical attention. What an exciting opportunity to support our health, animals and the environment.

Listen to my full conversation with Walter Ross on Thrive on Plants, available on Apple Podcasts, YouTube, and Spotify.

Spacemilk: https://spacemilk.com/

Apple Podcasts: https://podcasts.apple.com/us/podcast/thrive-on-plants/id1793550910YouTube: https://www.youtube.com/@drdaphnebascom/videos

References

1. Briskey D, et al. Effect of yeast protein on muscle mass and performance in an adult population: a double-blind, randomised controlled trial. Journal of Food and Nutrition Research. 2024;12(5):292–300. https://pubs.sciepub.com/jfnr/12/5/9/

2. McKenna CF, et al. Postabsorptive and postprandial myofibrillar protein synthesis rates at rest and after resistance exercise in women with postmenopause. Journal of Applied Physiology. 2024;136(6):1388–1399. https://doi.org/10.1152/japplphysiol.00886.2023

3. Wilkinson DJ, et al. Evaluating the leucine trigger hypothesis to explain the post-prandial regulation of muscle protein synthesis in young and older adults: a systematic review. Frontiers in Nutrition. 2021;8:685165. https://pmc.ncbi.nlm.nih.gov/articles/PMC8295465/

4. Wilkinson DJ, et al. Association of postprandial postexercise muscle protein synthesis rates with dietary leucine: a systematic review. Physiological Reports. 2023. https://doi.org/10.14814/phy2.15775

5. Simpson SJ, et al. Weight gain during the menopause transition: evidence for a mechanism dependent on protein leverage. BJOG. 2023;130(1):100–108. https://doi.org/10.1111/1471-0528.17290

6. Clean Label Project. Protein Powder Category Report 2023–2024. https://cleanlabelproject.org/protein-study/

7. Consumer Reports. Protein powder investigation. October 2025. https://www.consumerreports.org

8. NextFerm Technologies. ProteVin DIAAS and amino acid profile data. https://nextferm.com/protevin/ (Manufacturer-supplied data; independent peer-reviewed replication pending.)