The short version:
Whey protein wasn't always the default — for most of the 20th century it was a dairy byproduct farmers fed to pigs, and it only became a supplement once membrane filtration technology in the 1970s made it possible to turn liquid whey into a clean, soluble powder. From there it took Designer Whey, Met-Rx, and decades of research to build the industry you see on shelves today. On bioavailability: whey isolate and egg protein sit at the top, casein absorbs slowly for a reason, and plant proteins (soy, pea, hemp, rice) each have a specific amino acid gap worth knowing before you pick one.
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Walk into any supplement store today and whey protein dominates the shelf. That wasn't always true. For most of the 20th century, whey — the watery liquid left behind after milk is curdled and strained to make cheese — was considered waste. Cheesemakers dumped it, fed it to livestock, or paid to have it hauled away. The idea that it could become one of the most studied, most effective muscle-building supplements in the world would have sounded absurd to a dairy farmer in 1950.
What changed wasn't a single discovery — it was a slow convergence of dairy processing technology, exercise science, and a bodybuilding industry hungry for better products. Understanding that history actually makes the bioavailability differences between today's protein powders easier to understand, so we're covering both together.
The technical breakthrough that made whey protein possible was ultrafiltration — a membrane filtration process that became commercially viable for dairy processing in the early-to-mid 1970s. Before ultrafiltration, there was no practical way to separate whey's protein from its lactose, minerals, and water at scale. Ultrafiltration changed that, followed by ion-exchange and microfiltration refinements that let manufacturers strip out more and more of the non-protein content. The result: Whey Protein Concentrate first, and later — once filtration got even more precise — Whey Protein Isolate.
Even with the technology in place, whey protein's reputation as a muscle-building supplement took real scientific evidence to establish. The landmark study came in 1997, when researchers gave healthy adults a single meal containing either intrinsically labeled whey or casein and tracked exactly how the amino acids were used. Whey — digested quickly — caused a sharp, brief spike in blood amino acids and stimulated protein synthesis by 68%. Casein, which digests far more slowly, produced a longer, gentler rise and suppressed protein breakdown instead. This is the study that coined the "fast protein" versus "slow protein" framework that still shapes how people think about whey and casein today.
A follow-up trial in 2009 pushed the comparison further, testing whey hydrolysate against casein and soy protein isolate, both at rest and after resistance training. Whey produced the largest rise in blood essential amino acids, branched-chain amino acids, and leucine specifically — and the greatest muscle protein synthesis response of the three. Combined, these two studies are a big part of why whey became the reference standard everyone else gets compared to.
Having the technology to produce whey protein didn't automatically make it a good consumer product — early whey powders were notorious for tasting chalky and gritty, and mixing poorly. That started to change with Next Proteins International, founded in 1988 in Carlsbad, California by David Jenkins, a three-time Olympic sprinter with a background in chemical engineering. The company's early product was a meal-replacement drink called Pro Optibol, but its most influential launch came in 1993 with Designer Whey — widely credited as one of the first instantized, genuinely palatable whey protein powders marketed to the general consumer, not just hardcore bodybuilders.
Designer Whey's arrival in mainstream health food stores mattered because it helped separate "protein powder" from "bodybuilding powder" in the public's mind — a shift that eventually made whey the default protein source it is today, rather than a niche product for competitive lifters.
Around the same time, a physician named Dr. A. Scott Connelly was working on a different problem: preventing muscle wasting in critically ill hospital patients. That research became the foundation for Met-Rx, founded in 1991 around a proprietary protein blend called Metamyosyn — a deliberate mix of whey protein, calcium caseinate, egg albumin, and milk protein isolate, designed to combine fast and slow-digesting proteins in one product.
Met-Rx is widely credited with creating an entirely new product category: the meal replacement powder, or MRP. Marketed heavily within the bodybuilding world — including a partnership with Bill Phillips, who later built EAS and the "Body-for-Life" brand — Met-Rx grew from a niche product into a supplement industry giant, eventually selling for $108 million in 2000. The MRP category it created is still a recognizable shelf category in supplement stores today.
Long before Designer Whey or Met-Rx, Joe Weider — the bodybuilding entrepreneur behind Muscle & Fitness magazine and the Mr. Olympia contest — was already selling protein supplements. Weider advertised a "Hi-Protein Muscle Building Supplement" as early as 1952, decades before whey processing technology existed. His mass-gain formula of that era, marketed under names like "Crash Weight Gain" and later "Formula No. 7," was actually soy-based rather than the milk or egg protein you might expect — a detail that's easy to miss given how recently plant protein has been framed as a modern trend.
Weider's early marketing also produced one of the industry's more notorious cautionary tales. In 1972, the FTC scrutinized Formula No. 7 over its "gain a pound a day" claims — a case in which Arnold Schwarzenegger, then a rising bodybuilder under Weider's sponsorship, testified. The episode is a useful reminder that supplement marketing overpromising results is not a new problem invented by the internet — it's been part of this industry since the beginning.
Not all protein is created equal, and there are two standard scoring systems used to describe how well the body can actually use a given protein source. PDCAAS (Protein Digestibility-Corrected Amino Acid Score) has been the standard for decades, but it has known limitations — it caps scores at 1.0 even when a protein technically scores higher, and it estimates digestibility using fecal measurements rather than what's actually absorbed in the small intestine.
DIAAS (Digestible Indispensable Amino Acid Score) is the newer, more precise alternative, measuring amino acid digestibility at the end of the small intestine rather than after the gut microbiome has already altered things. DIAAS scores aren't capped at 1.0, which is why you'll see whey and egg scoring above 1.0 — genuinely excellent, not just "complete." We'll use DIAAS where it's available below, since it's the more accurate picture.
| Protein Type | DIAAS (approx.) | Digestion Speed | Main Amino Acid Gap |
|---|---|---|---|
| Whey Isolate | ~1.09+ | Very fast | None significant |
| Whey Concentrate | ~1.0 | Fast | None significant |
| Egg Protein | ~1.13 | Medium | None significant |
| Casein | ~1.05 | Slow (gels in stomach) | None significant |
| Soy Isolate | ~0.90 | Medium-fast | Methionine (mild) |
| Pea Protein | ~0.82 | Medium-fast | Methionine/cysteine |
| Hemp Protein | Not well established | Medium | Lysine |
| Brown Rice Protein | ~0.37–0.60 | Medium | Lysine (significant) |
DIAAS values vary by source, processing method, and specific product tested — treat these as approximate ranges, not fixed universal numbers. Hemp protein in particular lacks a well-established, widely-cited DIAAS value in the literature.
Filtered further than concentrate, isolate strips out most of the lactose and fat, landing around 90%+ protein by weight. It digests very fast, has a complete amino acid profile, and posts some of the highest DIAAS scores of any protein source tested. The tradeoff is cost — more filtration means a more expensive product for a modest purity gain over concentrate for most people. See our full Whey Protein guide for dosing specifics.
Casein's defining trait is what it does in your stomach: it forms a gel on contact with stomach acid, which slows gastric emptying and releases amino acids into the bloodstream over several hours instead of one sharp spike. That's the entire case for taking it before bed or between long gaps without food — it's not "better" than whey, it's built for a different job. See our Casein Protein guide for more.
Before whey processing technology existed, egg protein was the reference standard researchers measured other proteins against — its amino acid profile is genuinely excellent, and its DIAAS score rivals whey isolate. It's also a practical option for people avoiding dairy without wanting a plant-based protein, though it's less common on shelves now that whey dominates the category it once defined.
Soy protein isolate is the strongest plant option on paper, with a DIAAS close to whey concentrate and only a mild methionine gap — but taste and digestive tolerance vary more person to person than with dairy proteins. Pea protein has genuine human trial data showing muscle-building results comparable to whey, and is naturally low in methionine but high in lysine — see our Pea Protein guide.
Hemp protein is limited primarily by lysine and lacks strong published bioavailability data, making it more of a supplementary fiber-and-fat-rich option than a primary protein source. Brown rice protein has the weakest DIAAS of the group, held back significantly by low lysine — which is exactly why pea and rice protein are so often blended together, since rice is comparatively strong where pea is weak, and vice versa.
With this many options, the decision usually comes down to goal and tolerance, not one "best" protein:
There's no wrong answer here as long as you're covering your daily protein target — the differences between these options are real, but smaller than the difference between hitting your protein target and not.
Whey protein's dominance today is the product of a specific, traceable history — 1970s filtration technology that made it processable, a 1997 study that proved its fast-digesting advantage, and a run of companies (Designer Whey, Met-Rx, and Weider before either of them) that built the market and the product category around it. None of that happened because whey is magic; it happened because the technology, the research, and the marketing all lined up at the right time.
On the science itself: whey isolate and egg protein sit at the top of the bioavailability charts, casein trades speed for a slow, sustained release, and plant proteins each have a specific, well-documented amino acid gap rather than being uniformly "worse" — which is exactly why blended plant formulas exist. Pick based on your goal, your tolerance, and what you'll actually drink consistently, not on which one has the flashiest number on the label.
1. Boirie, Y., Dangin, M., Gachon, P., Vasson, M.P., Maubois, J.L., & Beaufrère, B. (1997). Slow and fast dietary proteins differently modulate postprandial protein accretion. Proceedings of the National Academy of Sciences, 94(26), 14930–14935.
2. Tang, J.E., Moore, D.R., Kujbida, G.W., Tarnopolsky, M.A., & Phillips, S.M. (2009). Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. Journal of Applied Physiology, 107(3), 987–992.
3. Mathai, J.K., Liu, Y., & Stein, H.H. (2017). Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS). British Journal of Nutrition, 117(4), 490–499.
4. Rutherfurd, S.M., Fanning, A.C., Miller, B.J., & Moughan, P.J. (2015). Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats. Journal of Nutrition, 145(2), 372–379.
5. Babault, N., et al. (2015). Pea proteins oral supplementation promotes muscle thickness gains during resistance training: a double-blind, randomized, placebo-controlled clinical trial vs. whey protein. Journal of the International Society of Sports Nutrition, 12, 3.
Company history details (Designer Whey, Met-Rx, Weider) are drawn from industry and archival reporting rather than peer-reviewed sources; specific dates are presented as accurately as available records allow. This article reflects general nutrition principles supported by the cited research and is not personalized medical advice. Always consult your physician before starting any supplement, especially if you have a food allergy or hormone-sensitive condition.