In a randomized crossover trial, 12 healthy men consumed 750 ml of semi-skimmed dairy milk, a standard oat-based drink (OBD), or a pea-protein-enriched oat drink (OBD+Pea) after an overnight fast. Over five hours, both oat drinks produced dramatically lower total amino acid responses versus dairy milk (OBD: −169,706 µM·min; OBD+Pea: −139,552 µM·min; both p<0.001), with essential amino acids similarly suppressed. Glucose spiked 0.86–1.73 mmol/L higher and insulin rose 1.8–2.1-fold faster with both oat drinks compared to milk. MRI revealed that the enriched oat drink emptied the stomach 48–84 ml faster than dairy milk between 60–120 minutes.
For adults focused on muscle preservation, healthy aging, and metabolic health, the gap is meaningful. Adequate essential amino acid — particularly leucine — delivery is a key driver of muscle protein synthesis, which declines with age and underlies sarcopenia risk. The finding that even protein-enriched plant alternatives fall significantly short of dairy's amino acid bioavailability reinforces a consistent pattern in the nutrition literature: plant protein quality, not just quantity, limits anabolic signalling. The sharper glucose and insulin responses also raise questions for individuals managing insulin sensitivity or metabolic syndrome. Critically, this is a preprint not yet peer-reviewed, so results may change. The sample is very small (n=12, men only), limiting generalisability to women and older adults. Overall, the work is confirmatory of known protein-quality differences but provides useful mechanistic detail via MRI gastric imaging.