CHAPTER 3 - Nutrigenetic Effect on Intestinal Absorption of Fat-Soluble Microconstituents (Vitamins A, E, D and K, Carotenoids and Phytosterols)

Abstract

The absorption efficiency of fat-soluble microconstituents (FSM) is very variable and depends on several factors such as the state of food (raw, processed, or cooked), the nature of dishes consumed with the FSM, the activities of digestive enzymes, and the efficiency of transport across the enterocyte. It has long been assumed that FSMs are absorbed by passive diffusion. However, in 2000 it was established that most newly absorbed phytosterols are effluxed, i.e., pumped back to the intestinal lumen, by two apical membrane transporters: the ATP-binding cassette G5 (ABCG5) and ABCG8. Recent studies have also shown that membrane transporters are involved in carotenoids and vitamin E absorption. Very recently a membrane transporter called STRA6 has been shown to be responsible for retinal (vitamin A) uptake by retinal pigment epithelium, and it is possible that it is the intestinal vitamin A transporter not yet identified. After being absorbed by the enterocyte, FSMs must be secreted into the body at the basolateral side of the cell. The discovery that transporters are involved in the intestinal absorption of FSMs is a key finding in the field of FSM bioavailability.