Modern Concepts of Regulation of Intestinal Nutrient Transport

Abstract

Humans, like other animals, insult their intestines with wildly varying food inputs. We start out life as 7-lb babies, consuming small amounts of food, all of it in the form of milk, yet we end up as adults weighing between 40 and 140 kg, consuming quantities of food one or two orders of magnitude greater than the intake of babies, mostly in the form of solids. If we’re lucky, we can eat whatever we want in whatever amounts we want: one day, a high-carbohydrate diet of elegant pastries; the next day, a no-carbohydrate, high-protein diet of filet mignon; the following day, neither pastry nor filet mignon, but a high-fat diet of rich cheese. If unlucky and poor, we may starve or occasionally get something to eat, but frequently suffer from deficiencies of vitamins, essential amino acids, or nitrogen. Even if living in affluence, we may be unlucky in other ways: we may develop diabetes or may require surgical resection of the intestine or else total parenteral nutrition. If working vigorously as lumberjacks, we may consume 7000 calories per day. Conversely, lying in bed all day requires only 800 calories. Half of us occasionally become pregnant, nurse one or more infants, and must increase our calorie intake correspondingly (up to several-fold in some nursing mammals).