Bodyweight development, efficiency of energy intake and small intestinal tissue morphology in young and old mice. 4 and 21-month-old mice were exposed to a low-fat or a high-fat diet for 2 weeks. (A) Bodyweight, (B) food intake and (C) fecal energy excretion were measured. (D) The efficiency of energy up-take was calculated and (E) villi length of the proximal, middle and distal part of the intestine in H&E stained paraffin sections was compared between young and old mice. In all figure the mean values ± SE were presented, young/low-fat n = 6, young/high-fat n = 6, old/low-fat n = 8, old/high-fat n = 8, *p < 0.05.