Impact of Maillard reaction products on nutrition and health: Current knowledge and need to understand their fate in the human digestive system

The Maillard Reaction (MR) is a non-enzymatic chemical reaction which results in the linkage between the amino group of amino acids and the carbonyl group of reduced sugars. MR products (MRPs) are common components of processed foods, mainly as a result of heating, especially in the Western diet. MRPs are classified as into three stages: initial, intermediate, and final stages, indicative of increased complexity and size, incurring different flavor, aroma, and texture. MRPs presence is known to reduce the nutritional quality of foods, particularly by reducing protein digestibility. Early reports have linked MRPs, especially advanced glycation end-products (AGEs) present in high concentration in the typical Western diet, to health conditions and diseases. However conflicting data has since been reported, and only a few (acrylamide, heterocyclic amines and 5-Hydroxymethylfurfural) MRPs have documented potential toxic or carcinogenic effects. High molecular weight MRPs are not available for direct absorption in the higher gastrointestinal tract, and are thus mostly metabolized by resident colonic microbes. MRPs have been the subject of sparse research interest in comparison with other non-digestible dietary elements. In this review, we outline the state of knowledge on MRPs in nutrition and health, and highlight the need to develop the limited knowledge on their impact on the gut microbiota and which metabolites derive from MRPs fermentation.