The relationship between nutrition and immune function is being widely recognized, although its study is relatively recent. The 1968 World Health Organisation monograph about “Interactions between Nutrition and Infection” presented the mechanisms linking infection and poor nutritional status. Following the development of immunology as a science, increasing evidence was obtained as well to show how undernutrition impaired resistance to infections and the immune response. It was initially recognized that deficits in certain micronutrients (like vitamins and minerals) had a direct impact on immune function. But the relationship between immune function and nutrition extends far beyond that, and the term immunonutrition has been coined. We are now aware of many conditions of nutritional imbalance (not all necessarily linked to nutritional deficiencies) that lead to impaired immune response. For instance, it is currently believed that nutrition is a key factor in the onset and development of many types of cancer, or that the dietary component of atherosclerosis risk can directly influence immune cells and the inflammatory response; certain nutrients, like seed and fish oils have been shown to respectively induce the release of pro- and anti-inflammatory mediators. Accordingly, the idea of undernutrition has been replaced by that of malnutrition, meaning that inappropriate nutrition or nutritional imbalance per se, whether it implies a nutrient deficit or not, influences immune function. That is the reason why overnutrition, or an excessive energy intake, is also now considered as malnutrition. In this chapter we will discuss three paradigmatic cases of malnutrition that have a strong immune and inflammatory impact: anorexia nervosa (AN) and bulimia nervosa (BN), as examples of severe undernutrition; obesity, also referred to as overnutrition; and celiac disease (CD), a pathological reaction of the body to a particular type of nutrients that leads to malnutrition. Although these nutrition-related diseases have different origins (psychological for eating disorders, modifiable lifestyle factors for obesity and autoimmune for CD), they all have in common to present an important inflammatory component and to have nutritional treatment as the main therapeutic approach.

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