Nutritional Assessment and Impact of the Mediterranean Diet on Patients With Inflammatory Bowel Disease

Inflammatory bowel diseases (IBD) comprise a variety of disorders that result from the continuous activation of the immunoinflammatory cascade, whose etiology has not been defined in some cases. Classical IBD include Crohn's disease (CD), ulcerative colitis (UC), and indeterminate colitis. These diseases are chronic and are characterized by alternating periods of recurrence and remission.

The European Society of Clinical Nutrition and Metabolism (ESPEN) defined malnutrition as a state resulting from lack of uptake or intake of nutrition leading to altered body composition (decreased fat-free mass and body cell mass), resulting in diminished physical and mental function and impaired clinical outcome from disease.

The prevalence of Malnutrition in patients with inflammatory bowel disease (IBD) is very high. it presents in up to 70% of patients with active disease and up to 38% in patients with remission.

Several factors contribute to the malnutrition in IBD including insufficient nutrient intake as a consequence of impaired appetite (anorexia, stomachache), short bowel syndrome, impaired nutrient absorption (diarrhea, villus atrophy, bowel resection, intestinal flora overgrowth), increased nutrient losses (bleeding, fistulae), and food-drug interaction.

Malnutrition in IBD has been associated with several adverse clinical outcomes. IBD patients with nutritional deficiencies may present with higher mortality rate, length of stay in the hospital, infectious rate, and even thromboembolic events than those without nutritional deficiencies. Furthermore, undernutrition in patients with postoperative conditions has been associated with increased complications such as anastomotic leakage and breakdown, infection including sepsis and pneumonia, prolonged hospitalization, and increased mortality.

IBD is clearly associated with intestinal dysbiosis. Changes in the microbiome have a pivotal role in determining the onset of the pathology, when the genetic background of the individual makes him/her predisposed and other concomitant environmental factors intervene. Results of studies aimed at characterizing the microbiota of patients suffering from IBD, even sometimes with checkered results, indicate a generalized decrease in biodiversity, measured by an appropriate parameter-alpha-as well as a reduction in specific taxa including Firmicutes and Bacteroidetes, Lactobacillus and Eubacterium. IBD patients also present a reduction in species producing butyrate, a short chain fatty acid positively modulating intestinal homeostasis and reducing inflammation.

Regarding environmental factors, accumulating data have proven that various nutritional components in diet can play a significant role in the development and clinical course of IBD. Dietary nutrients alter the composition of the gut microbiota and intestinal permeability, influencing the interaction between the host and gut microbiota.

The Mediterranean diet (MedDiet) is a nutritional model inspired by the traditional dietary pattern of some of the countries of the Mediterranean basin. Mediterranean dietary pattern (MDP) gather the following characteristics: abundant consumption of olive oil and high consumption of fruits, vegetables, cereals (preferably as whole grain), legumes, nuts and seeds. The MDP also includes moderate consumption of fish and shellfish, white meat, eggs, and fermented dairy products (cheese and yogurt), as well as relatively small amounts of red meat, processed meats, and foods rich in sugars. Frequent but moderate intake of wine, especially red wine with meals is also recommended.

Results from clinical and translational research on the Mediterranean diet point to its possible meaningful use in managing IBD, and thus additional studies could have the potential to add further insights to the field. Concerning published data, it was observed that 153 Italian healthy subjects were investigated for their dietary habits and their gut microbiota was assessed, and high-level adherence to a Mediterranean diet was found to beneficially impact the gut microbiota and associated metabolome. These studies provided the first concrete evidence for the interconnection between Mediterranean dietary patterns, gut microbiota and microbial metabolites as they observed that the consumption of fruit, vegetables and legumes by subjects with satisfactory adherence to the Mediterranean diet was associated with an increase in fecal SCFA levels, an effect that was likely boosted by bacteria belonging to both the Firmicutes and Bacteroidetes capable of degrading carbohydrates not digestible by the host. When eight adult patients suffering from CD followed the Mediterranean diet for 6 weeks, their transcriptome analysis showed a change in expression of more than 3000 genes; changes in the intestinal microbiota, although not significant, showed a trend towards normalization with an increase in the expression of Bacteroidetes (17.89% to 18.74%), Clostridium cluster IV (19.2% to 21.86%) and Clostridium cluster XIVa (26.78% to 28.79%) and a decrease in the abundance of Proteobacteria (5.93% to 5.48%) and Bacillaceae (4.65% to 4.21%).