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Context Protein digestion rate is the main factor influencing uptake in the body. Speeding up protein digestion rate can help ensure adequate absorption of the essential amino acids found in meat, making it a supportive nutritional strategy geared to older people struggling with declining muscle capacity and who are reluctant to increase their intake. However, protein digestion rate depends on a cluster of factors, particularly in the stomach where it depends on ability to quickly regain the optimal acidic pH after ingesting the food bolus, on the rate and viscosity of the gastric fluid getting mixed and churned by stomach muscle contractions, on pepsin secretion, on type of food, and on the size of the chewed-down bolus particles. Every one of these factors except type of food can decline with age and/or age-related diseases.

We developed a model to predict meat digestion as it transits through the stomach. The mathematical modelling is grounded in in vitro results, which means it can yield long-run predictions or information that may otherwise be impossible to obtain experimentally. The model combines the kinetics of pepsindriven protein degradation with laws governing pepsin diffusion and proton diffusion in food-bolus particles, all while accounting for the buffering capacity of the meat that slows the drop in pH. The results unsurprisingly show that the normally highly efficient digestion of meat proteins in the young adult stomach can rapidly collapse when they start to lose masticatory capacity or when gastric acid secretion and gastric motor function start to decline. The real benefit of this model is that it can quantify the in-stomach effect of the many factors that speed or slow protein digestion rate, and thus inform efforts to adapt foods to target populations—like the elderly.

The model could be expanded to factor in the effect of food–food interactions and then compared against in vivo measurements by nutritionists and physiologists on human subjects. It could also be transposed to other protein-rich food matrices, such as fish and dairy or plant-based protein foods.