Both of these groups can work very hard to breathe so a lot of their caloric intake is diverted to their respiratory muscles. In addition, because of their breathlessness and because their diaphragms push down on their stomachs, they cannot eat regular meals. Sometimes, smaller, more frequent meals are helpful. For cystic fibrosis patients, their chronic infections and impaired gastrointestinal absorption also contribute to their malnourished state. Nutritional supplements are usually indicated for these patients and in extreme cases, direct feeds into their GI tract through gastrotomy tubes may be in order.
Overweight patients are also at increased risk of complications related to the surgery.
Weight reduction can be extremely difficult because dieting should always be accompanied by a regimen of exercise. Exercise, needless to say, can be problematic for patients requiring a lung transplant. Weight reduction is always best accomplished under the auspices of a registered dietitian.