© 2005 American Society for Parenteral and Enteral Nutrition. The effect of bioactive nutrient molecules on inflammatory response has an archetype in Inflammatory Bowel Disease. The exacerbated inflammatory response in such conditions can be nutritionally modified by 2 ways: changing the response of the host, or changing the composition of the intestinal ecosystem. Host response can be modified by changing the cell structure and function which is nutrient dependent. Nutrient deprivation will lead to a situation where there is not enough building material for cell replacement and the synthesis of mediators (enzymes, hormones, etc). However, this may occur even in a situation where there is no quantitative nutrient deprivation but only qualitative changes. In Inflammatory Bowel Disease, changes in the sources of some nutrients such as lipids or carbohydrates (CHO) can modify the inflammatory response. Lipids, by changing cell membrane composition, may modify the pattern of eicosanoid synthesis, intracellular signal transmission and activation of nuclear transcription factors, which modify the expression of some genes - that is, changing the host response. On the other hand, certain sources of carbohydrates, by undergoing anaerobic bacterial fermentation, drop the pH in the intestinal lumen favoring the growth of certain strains of bacteria which act favorably in maintaining tolerance in the bowel. In addition, as a consequence of CHO fermention, short-chain fatty acids are produced which, especially butyrate, may act in 2 ways: by providing energy to the epithelial cells, but also as anti-inflammatory substrate - that is, modifying at least 1 of the mechanisms triggering the inflammatory response enhancement. However, it should not be forgotten that the cellular response to dietary modifications will depend on the individual genome, as has been recently observed. This may explain why some individuals do and others do not show a similar response to dietary interventions.