β-Lactoglobulin: A Superior Protein for Muscle Building?

What Is β-Lactoglobulin?

If you've ever used whey protein, you've consumed β-lactoglobulin (BLG). BLG is the dominant protein fraction within bovine whey, making up roughly 45–57% of it. What sets BLG apart from standard whey protein isolate (WPI) is its amino acid profile: BLG is naturally richer in essential amino acids (EAAs), and in particular it contains around 50% more leucine by weight compared to WPI (~15.7 g leucine per 100 g protein vs ~10.2 g for WPI).

That matters because leucine isn't just another building block. It acts as a molecular trigger for the mTOR signalling pathway — the cellular machinery that initiates muscle protein synthesis (MPS). Higher leucine availability tends to produce a stronger and faster activation of this pathway, which is why researchers and supplement manufacturers have become increasingly interested in leucine-enriched protein formulations.

The question a new 2025 study from the University of Nottingham [1] set out to answer was straightforward: does BLG's naturally higher leucine content actually translate into measurably greater muscle protein synthesis compared to a standard whey protein isolate, when both are given at the same total protein dose?

Study Design and Methods

The researchers used a randomised, double-blind, crossover design — one of the most rigorous approaches available for this type of comparison. Ten healthy young men (average age 26, average weight 81 kg) each completed two separate testing sessions, receiving either BLG or WPI on each visit, with neither the participants nor the researchers knowing which supplement was being given until after analysis. The two sessions were separated by a washout period of three to six weeks.

Both supplements were matched for total nitrogen content, delivering approximately 10 grams of protein each. This isonitrogenous design is crucial: it means any differences in outcome can be attributed to the composition of the protein — specifically the leucine content — rather than the total amount of protein consumed. BLG delivered 1.57 g of leucine per serving; WPI delivered 1.02 g.

On each testing day, participants arrived fasted after a minimum 10-hour overnight fast. The protocol involved a continuous intravenous infusion of a stable isotope leucine tracer — a safe, non-radioactive label that allows researchers to track precisely how much leucine is being incorporated into muscle proteins in real time. Three muscle biopsies were taken from the vastus lateralis (the large quadriceps muscle) at 0, 3, and 6 hours, with the protein supplement consumed immediately after the second biopsy at the 3-hour mark.

To test the combined effect of nutrition and exercise, participants also performed a bout of unilateral leg extensions (6 sets of 8 reps at 75% of their one-rep maximum) on one leg just before consuming the protein supplement. This allowed the researchers to compare MPS responses in a rested limb versus an exercised limb simultaneously, within the same session.

What the Blood Results Showed

Here the results were clear and statistically significant. After consuming both supplements, plasma concentrations of EAAs, branched-chain amino acids (BCAAs), and leucine rose rapidly, peaking at around 40 minutes post-consumption before returning towards baseline by 100–120 minutes.

However, BLG produced a meaningfully greater amino acid response. Peak plasma leucine was roughly 19% higher with BLG (396 µM vs 334 µM, p<0.001). When the total leucine exposure over time was measured (area under the curve), BLG delivered around 35% more than WPI. Similar advantages were seen for BCAAs and EAAs as a whole — all statistically significant.

Plasma insulin rose in both conditions following protein ingestion, peaking at comparable levels for BLG and WPI, with no significant difference between the two. This indicates the two supplements had similar insulinotropic effects at this dose.

What the Muscle Biopsy Results Showed

This is where the findings get both surprising and important to communicate accurately.

Both BLG and WPI significantly increased muscle protein synthesis from baseline — by approximately 52% in the fed, rested state and around 58% in the fed, exercised state. These are robust, meaningful increases. However — and this is the key finding — there was no statistically significant difference in MPS between BLG and WPI in either condition. Despite BLG delivering substantially more leucine into the bloodstream, that extra leucine did not translate into detectably greater muscle protein synthesis in this group of young, healthy men.

The researchers discuss why this might be the case. At 10 grams of protein, both supplements were already at what the literature describes as a "suboptimal" dose (around 20 grams is generally considered sufficient for maximal MPS stimulation in young adults). Yet both still robustly stimulated MPS. One interpretation is that even 1.02 g of leucine from WPI, alongside the other EAAs present, was sufficient to fully activate the mTOR pathway in these young participants — meaning BLG's additional leucine offered no further advantage in this population. In young, healthy individuals where anabolic resistance is low, there may be a ceiling effect: once you've crossed the leucine threshold, more leucine doesn't add more muscle-building signal.

Why This Still Matters: The Bigger Picture

So if BLG and WPI produce the same MPS in young adults, why should you care? Because the real promise of BLG may lie in a completely different population — and the study authors are explicit about this.

As we age, our muscles become progressively less responsive to protein nutrition — a phenomenon known as anabolic resistance. Older adults typically need more protein (and specifically more leucine) to stimulate the same degree of MPS that a smaller amount would trigger in a younger person. This is one of the key drivers of the gradual muscle loss, known as sarcopenia, that occurs with ageing and contributes significantly to frailty, falls, and loss of independence.

For older adults, or for clinical populations such as those recovering from surgery or illness, consuming large amounts of protein can be difficult. If BLG can deliver a higher leucine hit at a lower total protein dose, it could help overcome anabolic resistance in people who struggle to eat enough protein — achieving with 10 g what might otherwise require 20–25 g of standard whey. That is the hypothesis the authors want tested next, and it's a genuinely compelling one.

Additionally, BLG's superior amino acid bioavailability profile — higher peak leucinaemia, higher area under the curve for EAAs and BCAAs — remains a real biological advantage, even if its consequences for MPS weren't detectable in this particular study population. Whether that translates to meaningful differences in muscle mass over weeks and months of supplementation, particularly in more vulnerable populations, is an open and important question.

Practical Takeaways

For most healthy, active adults under 50, the evidence from this study suggests your current whey protein isolate is doing its job well. There is no proven advantage to switching to a BLG-specific supplement for the purpose of building more muscle per gram of protein — at least not based on current data in young adults.

Where the picture could change is for older adults, post-surgical patients, or anyone struggling to meet their daily protein targets. If BLG's superior leucine delivery can stimulate MPS comparably to larger protein doses in these populations, it could become a meaningful tool — whether as a supplement or as an ingredient in functional foods formulated for healthy ageing. That research is still to come, but the biological rationale is there.

In the meantime, the broader lesson holds: leucine content matters, not just total protein. Whether you're choosing between protein sources, planning post-workout meals, or thinking about how to support muscle health as you get older, keeping an eye on leucine density — rather than grams of protein alone — is a worthwhile habit.

References

1. Ely IA et al. "The Effect of Leucine-Enriched β-Lactoglobulin Versus an Isonitrogenous Whey Protein Isolate on Skeletal Muscle Protein Anabolism in Young Healthy Males", Nutrients 17 (2025) 3410. https://doi.org/10.3390/nu17213410