The story begins with a 2024 study, in which these researchers and their colleagues adapted a classic chemistry technique called the ninhydrin method.

Originally used in forensic science and lab settings to detect amino acids, the team modified it into a fast, affordable blood test. By filtering out large protein molecules from pig blood and then measuring smaller protein fragments both before and after breaking them down chemically, the researchers could work out how much dietary protein had been absorbed. Crucially, this also showed whether it entered the bloodstream as individual amino acids or as small chains called peptides. The method turned out to be accurate, reliable, and practical.

But the bigger breakthrough came in 2025. Pierzynowski, Pierzynowska and their colleagues used results from the same blood test to develop a mathematical algorithm that could do something no previous method had managed: distinguish between the three main forms in which digested protein enters the blood: free amino acids, dipeptides (two amino acids linked together), and tripeptides (chains of three).

In healthy pigs, the vast majority of absorbed dietary protein arrived in the blood as dipeptides and tripeptides, not as individual amino acids. Free amino acids typically accounted for only around 10–20% of the total.

The team’s research also showed that pancreatic enzymes play a crucial role. When they gave pigs with pancreatic insufficiency enzyme supplements, far more protein fragments were detected in the bloodstream after meals. Even amylase, an enzyme not traditionally associated with protein digestion, boosted peptide absorption.

The team’s simple, low-cost tool could one day help doctors fine-tune enzyme therapies for patients with conditions like cystic fibrosis or pancreatitis – while also deepening our understanding of how protein nutrition actually fuels the body at different ages or levels of physical training. It could also be used to compare the quality of different protein sources – such as natural, lab-produced, or sustainably produced proteins – in early testing, and potentially even in athletes.