What are nutrients and why are nutritional deficiencies such a hazard for those with Crohn disease?

The human body needs proteins, fats, calories, vitamins, and minerals to grow, build new cells and tissues, and carry out its many functions. Most of these nutrients are contained in the foods we eat. To ensure that we get all of the nutrients we need, we are advised to eat a balanced diet from the 4 food groups: meat and other proteins, dairy products, fruits and vegetables, and cereals and grains.
 
When we eat, foods are broken down in the stomach and intestines. Nutrients are absorbed through the wall of the small intestine, and the waste is eliminated as stool or feces when we have a bowel movement. This process is impaired in people with Crohn disease, and nutritional deficiencies can result. 

Nutritional deficiencies are a problem for almost everyone with Crohn disease, but they are most serious in children and teens who are still growing. Growth can be stunted permanently and sexual development (puberty) delayed in these young people. Girls and women can develop hormone imbalances and stop menstruating. Nutritional deficiencies also can prevent medications from working as well as they should in healthy people.
 
In general, nutritional deficiencies are not consistent with good health. They can make you to feel weak, tired, depressed, or just “blah.” They leave you vulnerable to infections and other diseases. They can stop anyone from looking, feeling, or performing at his or her best.