Surgery to the small intestine
Following resection of the small intestine in Crohn's disease, the remaining bowel usually adapts to increase its absorptive capacity and should be possible to build back up to a normal diet. However, if there has been extensive surgery, the absorptive capacity will be reduced. A high calorie diet will be required to prevent weight loss and high energy drinks available on prescription may be helpful. In a few cases it may be necessary to supplement food with a special feed delivered via a fine tube into the stomach, or into the blood.

If the terminal ileum is resected, Vitamin B12 may not be efficiently absorbed as this is the only part of the gut where absorption of this vitamin takes place. The body has a large store of Vitamin B12 but when this has been used up regular Vitamin B12 injections will be required to prevent development of a type of anaemia. Folic acid may also be poorly absorbed if there has been extensive surgery to the small bowel and may need supplementation also to prevent anaemia.

The intestine's reserve capacity for fat absorption is more limited than that for carbohydrate or protein, and a reduction in dietary fat may be helpful. This will need to be replaced with carbohydrate- and protein-rich foods and occasionally a special form of easily absorbed fat known as medium chain triglyceride to prevent weight loss. If fat malabsorption continues, the fat soluble Vitamins - Vitamins A and D, and minerals - calcium and magnesium, may be at risk of depletion.

Surgery to the large intestine
Resection of part of the large intestine in either Crohn's disease or ulcerative colitis does not usually require a special diet. After the operation, the diet will be built up gradually from liquids to a light diet and then back to a normal diet. If the whole of the large intestine is removed, an ileostomy or pouch will be formed. The small intestine needs some time to adapt to some of the functions of the large intestine and, at first, plenty of fluids and salt are required. It is advisable not to take too much fibre initially to reduce output from the stoma, but this can be gradually increased to suit the individual. Absorption of nutrients is usually normal, (unless, in the case of Crohn's disease, some of the terminal ileum has also been removed) and therefore patients should keep to a normal varied diet. Patients with ileostomies may prefer to avoid foods which cause an unacceptable odour such as onions, lentils, pulses and sprouts.