Correlation between in vitro and in vivo data on food digestion. What can we predict with static in vitro digestion models?

During the last decade, there has been a growing interest in understanding food's digestive fate in order to strengthen the possible effects of food on human health. Ideally, food digestion should be studied in vivo on humans but this is not always ethically and financially possible. Therefore, simple in vitro digestion models mimicking the gastrointestinal tract have been proposed as alternatives to in vivo experiments. Thus, it is no surprise that these models are increasingly used by the scientific community, although their various limitations to fully mirror the complexity of the digestive tract. Therefore, the objective of the present work was to call upon the collective experiences of scientists involved in INFOGEST (an international network on food digestion) to review and reflect on the applications of in vitro digestion models, the parameters assessed in such studies and the physiological relevance of the data generated when compared to in vivo data. The authors provide a comprehensive overview of in vitro and in vivo digestion studies investigating the digestion of macronutrients (i.e. proteins, lipids and carbohydrates) as well as studies of the bioaccessibility and bioavailability of micronutrients and phytochemicals. Although in vitro static models are over-simplistic and do not reproduce all the dynamic aspects of the gastrointestinal tract, they are increasingly useful in predicting in vivo digestion in some cases like determination of a glycaemic index, ranking of protein according to their digestibility and lipolysis of simple emulsions. Regarding micronutrients, relative carotenoids in vitro bioaccessibility reasonably predicts in vivo bioavailability whereas in the case of polyphenols, prediction is more problematic. This leaves a vast room for future studies and improvements