Plant proteins have long been treated as the weaker option for building muscle. A new randomized trial suggests corn protein may be an exception. In older adults, 20 g of corn protein stimulated muscle protein synthesis (MPS) about as well as 20 g of milk protein. Here is what the study found, and what it can't tell you yet.
The Study: Corn Protein Versus Milk
The paper, published in The Journal of Nutrition by Lim and colleagues (DOI: 10.1016/j.tjnut.2026.101895; PubMed 42933646), tested a question that had not been examined in older adults. Plant proteins usually have lower essential amino acid content, especially leucine, so they are generally considered less anabolic than animal proteins. The authors point out that corn protein is unusual because its leucine content is relatively high. Older adults also show reduced anabolic sensitivity, which makes them a demanding test group.
The researchers ran a double-blind, placebo-controlled, randomized parallel-group trial with 48 healthy older adults (average age 68 ± 5; 24 men and 24 women). Participants received 20 g of one of four things:
- CORN: corn protein isolate
- PEA+CORN: a pea and corn protein blend
- MILK: milk protein isolate
- PLA: a non-protein, low-energy placebo
Everyone did unilateral knee extension exercise (3 sets of 10 repetitions at 75% of one-repetition maximum). MPS was measured with a primed continuous infusion of L-[ring-13C6] phenylalanine, with blood and muscle samples taken throughout.
The Headline Numbers
The increase in MPS over basal values was:
| Group | MPS increase vs. basal |
|---|---|
| Corn protein | 216 ± 170% (P < 0.001) |
| Pea + corn blend | 217 ± 167% (P = 0.001) |
| Milk protein | 138 ± 78% (P = 0.033) |
| Placebo | 77 ± 46% |
All three protein groups beat placebo, and the authors report no differences between the protein groups. The corn and blend averages were numerically higher than milk, but the spread was wide (note the large standard deviations), so the fair reading is "comparable," not "better." Don't read it as corn beating milk.
Exercise Still Matters
Resistance exercise further increased MPS compared with supplementation alone in every group (all P < 0.001). Protein helps, but lifting amplified the response regardless of the protein source. For older lifters, the paper supports pairing protein with training rather than relying on either one alone.
Why Leucine Gets the Spotlight
Leucine is the amino acid most associated with switching on the muscle-building response. Plant proteins often fall short on it, which is why they are usually assumed to be less effective per gram. The authors frame corn protein's relatively high leucine content as the reason it might behave differently. The abstract does not give leucine figures or test leucine as the cause, so treat that explanation as the paper's rationale, not a proven mechanism.
Practical Takeaways
Dose: The study used 20 g of protein per serving. That is the only dose tested, so it is the evidence-based number to anchor on. The trial didn't compare other amounts.
Timing: The abstract describes participants consuming the protein around a single bout of leg exercise. It doesn't test different timing windows, so it can't tell you whether before, during, or after is best.
Who it may suit:
- Older lifters: This is the population studied (healthy adults around 68), and the response held up despite the age-related blunting of anabolic sensitivity.
- People limiting dairy or animal products: Corn protein and a pea-corn blend produced MPS responses similar to milk protein. The participants were not selected as vegans, so this is an inference from the protein source, not a result in vegan eaters.
- Anyone building a plant-based protein mix: The pea-corn blend performed as well as corn alone, which suggests blending is a workable option.
Who should be cautious or skip it:
- People with a corn allergy or sensitivity: The study doesn't address this, but it is the obvious practical exclusion.
- Anyone expecting proof of long-term muscle gains: This trial measured MPS, a short-term mechanistic marker, not changes in muscle size or strength over weeks or months.
- People with medical conditions: Participants were healthy older adults. The findings may not carry over to those with kidney disease, frailty, or other illnesses, so check with a clinician first.
The Fine Print
Three caveats matter. First, 48 participants split across four groups is a small sample, and the wide variability in the corn groups means individual responses differed a lot. Second, MPS over a short measurement window is not the same as muscle growth over time. Third, the placebo group also showed an MPS rise of 77% from baseline, which is a reminder that exercise and measurement context affect these numbers, so interpret the percentages within the study design.
Bottom Line
The conclusion in the paper is straightforward: 20 g of corn protein, a pea-corn blend, or milk protein raised MPS in healthy older adults, and resistance exercise boosted the response further. For people who want a plant-based option without assuming a trade-off in anabolic response, corn protein is now a credible candidate. Longer training trials will show whether the short-term advantage translates into actual muscle and strength gains.
Source: Lim et al., The Journal of Nutrition. Trial registration NCT05917223. PubMed: https://pubmed.ncbi.nlm.nih.gov/42933646/
