Disease-related weight loss occurs frequently in inflammatory bowel disease (IBD). Approximately 65% to 75% of patients with Crohn’s disease (CD) and 20% to 60% of patients with ulcerative colitis (UC) experience significant weight loss (1,2). Malnutrition is associated with compromised surgical outcomes, delayed wound healing, and increased length of hospital stay. In addition, malnourished patients with IBD have significantly impaired quality-of-life scores compared to IBD patients with a normal nutritional status (3).

Vitamin and mineral deficiencies are also common in IBD, even in patients without weight loss or obvious protein and/or calorie malnutrition (4, 5 and 6). Vitamin D, calcium, and vitamin K inadequacies are of particular importance because of their connection to bone health (7). It is estimated that 50% of patients with IBD have osteopenia and 15% have frank osteoporosis, resulting in a 40% greater incidence of fractures in those with IBD than in the general population (8,9).

Decreased food intake is common in patients with abdominal pain, nausea, or chronic diarrhea and is the most evident contributor to malnutrition in IBD. Unnecessary and overly restricted diets also contribute to malnutrition. Patients may eliminate entire categories of foods such as dairy products, fruits, vegetables, and whole grains as a result of perceived food intolerance as well as inappropriate advice from health professionals, friends, or the media (10).

Malabsorption can occur in the presence of extensive small bowel inflammation, mucosal injury, or resections of large portions of small bowel. The degree of malabsorption is related to the length of bowel resection, the location of the resected segment, and the quality of the remaining bowel. Loss of the terminal portion of the ileum is especially significant, as this portion of the bowel is responsible for the reabsorption of bile salts. Resection of the terminal ileum with loss of the ileal-cecal valve can also result in malabsorption through small bowel bacterial overgrowth.

Traditionally, serum proteins such as albumin and prealbumin have been regarded as indicators of nutritional status. However, the serum levels of these proteins are decreased by inflammatory conditions regardless of intake or body composition and are therefore not valid indicators of nutritional status (11).

Unplanned weight loss of >10% of usual weight and poor oral intake for >2 weeks are practical indicators of compromised nutritional status. (See Table 18.1 for other components of nutrition assessment.) Percentage of ideal weight and body mass index (BMI) are not absolute indicators of nutritional status. In an era of epidemic obesity, clinicians will increasingly encounter patients with significant malnutrition who have experienced weight loss, but still remain overweight or obese.
In contrast, some patients who are below “ideal weight” may still have a normal nutritional status. However, patients who are <85% of ideal weight or those with a BMI >18 will experience a more rapid onset of malnutrition and should receive close scrutiny of nutritional status and oral intake.

Subjective Global Assessment (SGA) is a tool to determine a patient’s nutritional status that can be rapidly taught, is reproducible, and correlates with functional status (12). SGA assesses weight change, dietary intake, gastrointestinal (GI) symptoms, functional impairment, and physical examination. However, SGA is not useful for identifying specific vitamin and mineral deficiencies. Therefore, examination of the patient’s eyes, hair, nails, skin, oral cavity, and neurological capacity, in conjunction with serum nutrient levels, is necessary to identify vitamin and mineral deficiencies.

A vital component of nutrition assessment in patients with extensive or multiple bowel resections is establishing the length and anatomy of the remaining bowel. In patients without complete surgical records, a radiological contrast study to establish the length of remaining bowel will provide insight into likely nutritional inadequacies and the potential need for parenteral nutrition (PN) (Table 18.1).

Patients with IBD do not generally have extraordinary caloric needs. Physical activity is inversely related to disease activity; therefore, an increase in metabolism secondary to illness is often balanced with a decrease in physical activity (13,14). A range of 25 to 35 kcal/kg/day is adequate for many adult IBD patients (14,15). Patients with a BMI <18 will require increased calories per kilogram compared to “normal”-weight patients because they have more metabolically active tissue per kilogram and consequently, will often require additional calories for weight gain (16). However, it is very important to remember that those patients with significant malnutrition should receive a reduced initial calorie provision (15 to 20 cal/kg) due to the risk of refeeding syndrome.

Patients with IBD may also require greater protein intake to maintain nutritional status and to support lean muscle mass. Episodes of inflammation and corticosteroids induce a negative nitrogen balance with loss of lean muscle mass. Additionally, protein losses occur in areas of inflamed and ulcerated intestinal mucosa via defects in epithelial tight junctions (17). To maintain positive nitrogen balance, 1.3 to 1.5 g/kg/protein/day is recommended (17). Severely malnourished patients and those recovering from surgical procedures may require up to 2.0 g/kg/protein/day (17). Patients with persistent losses from wounds, surgical drains, or fistulas may require still greater protein intake to maintain nitrogen balance.

Contrary to common beliefs and practices, there is no specific dietary regimen with proven efficacy for reducing disease activity in IBD. Healthcare providers frequently recommend that patients with IBD restrict lactose-containing foods; however, there is inadequate evidence to support withholding lactose in IBD patients who are not symptomatic after ingestion of normal amounts of lactose. In the United States, only 6% of CD patients and 9% of UC patients report GI distress after consumption of dairy products, which is less than the incidence of lactose intolerance among the general population (18,19). Dairy products are valuable sources of vitamin D, calcium, and high-quality protein; therefore, it is inadvisable to routinely restrict lactose in patients with IBD. Those patients with conclusive lactose malabsorption should limit dairy products or consume dairy products with a lactase supplement to decrease diarrhea and intestinal gas.

Low-fiber diets are frequently recommended to patients with stricturing CD. However, there are no controlled investigations that demonstrate that a low-fiber diet leads to symptom improvement, decreased hospitalizations, or decreased incidence of small bowel obstruction. Levenstein et al. reported no beneficial effect from a low-residue diet in CD patients without strictures as compared to controls (20).