PAN Prodig - True Ileal Digestibility of Different Plant-Based Proteins in a Human Ileostomy Model

Background

When comparing sources of animal- and plant protein, latter have a lower environmental impact and are superior regarding their nutritional value, as they contain a variety of different vitamins, minerals and dietary fibre which have been linked to positive health outcomes1. In contrast, protein quality and digestibility of plant-based protein are lower in comparison to animal-based protein which is attributed to the incomplete amino acid profile and the presence of antinutritional factors imparing protein digestibility and utilisation as well as the absorption of certain minerals2,3.

As a consequence of reduced digestibility, undigested proteins and unabsorbed amino acids reach the colon where they become substrates for proteolytic fermentation by our microbiota. This fermentation process results in the production of a variety of different metabolites, such as branched-chain fatty acids, ammonia, phenols, indoles, p-cresol as well as hydrogen sulphide – depending on the underlying amino acid and microbiota composition. Some of these metabolites were shown to have detrimental effects on health by causing inflammation or by potentially being carcinogenic4.  

These findings highlight the importance to study the digestibility of different protein sources, specifically to investigate which proteins and amino acids withstand digestion and absorption and can therefore be fermented, to increase the understanding of resulting health effects.

To date, there are several in vitro models available to simulate digestibility of proteins e.g. with low and high bioavailability. However, these models face limitations such as accurately modelling gastric emptying and brush border enzyme activity5. Consequently, previous research has included ileostomy patients to obtain in vivo data on true ileal digestibility of different protein sources by collecting digesta content of ileostomy bags6,7.

Nonetheless, the majority of human in vivo studies focused on animal or soy proteins, leaving a gap in knowledge regarding newer plant-based protein sources.

Objectives

The study aims to investigate how differences in bioavailability of plant-based proteins affect true ileal digestibility in ileostomates and to identify plant-based dietary compounds that escape digestion and absorption, making them available for colonic fermentation.

The underlying primary outcome is defined as differences in the true ileal digestibility. The secondary outcomes include changes in protein and metabolite profiles in the collected digesta, determined by proteomic and metabolomic analyses.

Additionally, results from the human ileostomy model will be compared with results from in vitro digestion according to the Infogest 2.0 protocol for each of the tested plant-based proteins.

References:

1. Sabaté, J., Sranacharoenpong, K., Harwatt, H., Wien, M., & Soret, S. (2015). The environmental cost of protein food choices. Public Health Nutrition, 18(11), 2067–2073. https://doi.org/10.1017/S1368980014002377

2. Ferrari, L., Panaite, S.-A., Bertazzo, A., & Visioli, F. (2022). Animal- and Plant-Based Protein Sources: A Scoping Review of Human Health Outcomes and Environmental Impact. Nutrients, 14(23), 5115. https://doi.org/10.3390/nu14235115

3. Hertzler, S. R., Lieblein-Boff, J. C., Weiler, M., & Allgeier, C. (2020). Plant Proteins: Assessing Their Nutritional Quality and Effects on Health and Physical Function. Nutrients, 12(12), 3704. https://doi.org/10.3390/nu12123704

4. Peled, S., & Livney, Y. D. (2021). The role of dietary proteins and carbohydrates in gut microbiome composition and activity: A review. Food Hydrocolloids, 120, 106911. https://doi.org/10.1016/j.foodhyd.2021.106911

5. Ariëns, R. M. C., Bastiaan-Net, S., van de Berg-Somhorst, D. B. P. M., El Bachrioui, K., Boudewijn, A., van den Dool, R. T. M., de Jong, G. A. H., Wichers, H. J., & Mes, J. J. (2021). Comparing nutritional and digestibility aspects of sustainable proteins using the INFOGEST digestion protocol. Journal of Functional Foods, 87, 104748. https://doi.org/10.1016/j.jff.2021.104748

6. Moughan, P. J., Butts, C. A., van Wijk, H., Rowan, A. M., & Reynolds, G. W. (2005). An Acute Ileal Amino Acid Digestibility Assay Is a Valid Procedure for Use in Human Ileostomates. The Journal of Nutrition, 135(3), 404–409. https://doi.org/10.1093/jn/135.3.404

7. Bos, C., Airinei, G., Mariotti, F., Benamouzig, R., Bérot, S., Evrard, J., Fénart, E., Tomé, D., & Gaudichon, C. (2007). The Poor Digestibility of Rapeseed Protein Is Balanced by Its Very High Metabolic Utilization in Humans. The Journal of Nutrition, 137(3), 594–600. https://doi.org/10.1093/jn/137.3.594