Systematic review: adipose tissue, obesity and gastrointestinal diseases

Background Obesity is increasingly being recognized as a risk factor for a number of benign and malignant gastrointestinal conditions. However, literature on the underlying pathophysiological mechanisms is sparse and ambiguous. Insulin resistance is the most widely accepted link between obesity and disease, particularly colorectal cancer. The recognition that intra-abdominal fat is immunologically active sheds new light not only on the pathogenesis of obesity-related gastrointestinal conditions, but also on inflammatory conditions such as Crohn's disease. Aim To describe the biology of adipose tissue, its impact on the immune system and explores the possible underlying mechanisms linking obesity to gastrointestinal diseases. It also looks at the role of mesenteric fat in determining severity and course of Crohn's disease. Methods Relevant English-language literature and abstracts cited on MEDLINE database were reviewed. Results Our recent finding of an association between obesity and subclinical bowel inflammation suggests that, apart from promoting generalized immune activation, fat also evokes local immune responses. We propose that the proinflammatory milieu promoted by obesity could underlie many of these associations and that the mechanism implicating insulin resistance may merely represent an epiphenomenon. In Crohn's disease, on the other hand, intra-abdominal fat may provide a protective mechanism. Conclusion The potential of adipose tissue as a therapeutic target is vast and needs exploration.