Crohn’s disease (CD) is a chronic intestinal disorder of unknown etiology that may involve any part of the gastrointestinal tract. The small bowel is involved in 70% of CD patients.

Undernutrition expressed in low body mass index (BMI) <18.5 kg/m², is a common presentation and has been reported in 65–75% of these patients. Possible pathogenic mechanisms include inadequate dietary intake ,increased energy expenditure, nutrient malabsorption and intestinal losses. We have studied recently these three important components of energy balance of underweight crohn’s patients and found that nutrient malabsorption may play a role.

Although the majority of crohn's disease patients are undernourished , some of them are surprisingly obese and their symptoms seem be more severe; Blain A et al. have reported recently that obesity in CD has been associated with more frequent anoperineal complications and a more marked disease activity. Hass J et al have found that overweight CD patients require earlier surgical intervention and perhaps more aggressive medical therapy. Notwithstanding, the characteristics of CD and possible underlying pathophysiological mechanisms in obese patients have not been studied yet.

Mesenteric hypertrophied fat commonly called “creeping fat is a common feature of crohn's disease and has been reported to correlate with ulceration, stricture formation and transmural inflammation. It is a matter of debate whether the development of creeping fat is a causative or secondary phenomenon ,but there is increasing body of evidence that suggest that mesenteric adipose tissue plays an active role in the pathogenesis of creeping fat and mesenteric inflammation by pro-inflammatory and anti-inflammatory adipocytokines.

Recently there is more recognition that adipose tissue is not a passive connective tissue merely storing fat but an activeendocrine organ which participates in numerous physiological and pathophysiological processes with variety of secretory products designated adipocytokines that regulate metabolic processes in an endocrine ,paracrine and autocrine manner Moreover, Obesity is increasingly being recognized as a risk factor for a number of gastrointestinal conditions as well as being characterized by a chronic, systemic low-grade state of inflammation per se. Biomarkers of inflammation, such as the leukocyte count, tumor necrosis factor-alpha (TNF-alpha), interleukin 6 (IL-6), and C-reactive protein, are increased in obesity and have been related to insulin resistance and the metabolic syndrome.