Chronic but not acute energy restriction increases intestinal nutrient transport in mice

Chronic energy restriction (ER) dramatically enhances intestinal absorption of nutrients by aged mice. Do adaptations in nutrient absorption develop o nly after extended ER or immediately after its initiation? To determine the time course of adaptations, we measured rates of intestinal glucose, fruct ose and proline transport 1-270 d after initiation of ER (70% of ad libitum ) in 3-mo old mice. Mice of the same age that consumed food ad libitum (AL) sewed as controls; a third group was starved for 1 or 2 d only, to disting uish the effects of acute ER from those of starvation. Acute ER of 1, 2 and 10 d had no effect on nutrient absorption. Starvation significantly decrea sed intestinal mass per centimeter, thereby reducing transport per centimet er and intestinal absorptive capacity without significantly altering transp ort per milligram of intestine. ER for 24 d enhanced only fructose uptake, whereas ER for 270 d enhanced uptake of all nutrients by 20-100%. Despite m arked differences in body weights, the wet weights of the stomach, small in testine, cecum and large intestine were generally similar in AL and ER mice , suggesting that the gastrointestinal tract was spared during ER. In contr ast, the wet weights of the lungs, kidneys, spleen, heart, pancreas and liv er each differed by 40-120% between ER and AL mice. Intestinal transport ad aptations develop gradually during ER, and the main mechanism underlying th ese adaptations is a dramatic increase in transport activity per milligram tissue.