Gastric digestion of whey protein gels: A randomized cross-over trial with the use of MRI

Food structure affects the breakdown kinetics of food. This has been extensively studied via in vitro digestion models. However, these in vitro findings need to be verified in vivo. Previously, we found that MRI parameters (T1 and T2 relaxation times) can serve as markers of protein digestion. Here, we assessed the effect of food hardness and protein content on gastric emptying as well as the application of these MRI parameters to monitor in vivo gastric digestion of solid foods. In a randomized cross-over trial, 18 healthy males (age: 27 +/- 5 y; BMI 23 +/- 1 kg/ m2) ingested three gels: a soft gel with low protein content (Soft-LP), a hard gel with low protein content (Hard -LP), and a hard gel with high protein content (Hard-HP). Before and every 10 min after ingestion till 85 min, abdominal MRI scans were obtained to determine the gastric content volume and T1 and T2 of the gastric content. The decrease in gastric content volume differed among gels: Hard-HP < Hard-LP < Soft-LP. For all gels, mean T1 and T2 of the measured stomach content decreased directly after ingestion and then after 15 min gradually increased with Hard-HP < Hard-LP < Soft-LP. In conclusion, high protein content and high hardness slowed gastric emptying down. In addition, we show that T1 and T2 measurements provide extra information on the dilution and digestion of solid foods in the stomach. This underpins the potential of MRI to provide insights into in vivo protein digestion and link in vitro and in vivo digestion research.