The Effects of a Modified Mediterranean Diet on Ulcerative Colitis Patients

Ulcerative colitis (UC) is a chronic, inflammatory, non-contagious disease affecting the mucosa of the large intestine and rectum characterized by periods of exacerbation and remission. While the exact causes of UC aren't fully understood, the disease's etiology is linked to a complex interaction of genetic, immunological, and environmental factors, including gut microbiota dysbiosis. Therapeutic approaches for UC aim to reduce inflammation, control symptoms, maintain remission, and improve patients' quality of life. Key therapeutic approaches include aminosalicylates, glucocorticoids, immunosuppressants, biological therapy, and small molecules.

The gold standard for monitoring disease activity and treatment response is endoscopy, supplemented by fecal calprotectin and C-reactive protein as biomarkers, and intestinal ultrasound as an imaging method. Given the invasive nature of endoscopy in assessing disease activity, there's an increasing emphasis on non-invasive monitoring methods. These are often insufficient, highlighting a need for new inflammatory markers.

Galectin-3 is a protein from the lectin family associated with inflammatory and fibrotic processes. It's being investigated as a prognostic and/or diagnostic biomarker in various diseases and conditions, and its association with UC has already been demonstrated; it can be measured in serum.

Dietary habits play an important role in the prevention and treatment of numerous diseases and conditions, including UC.

Current European and Croatian guidelines for nutrition in patients with inflammatory bowel disease emphasize recognizing malnutrition and meeting the body's nutritional needs through enteral and parenteral support, along with individual mineral and element supplementation. However, these guidelines don't single out any specific dietary pattern for inducing or maintaining disease remission. Patients have clearly expressed a need for dietary counseling and often independently adopt restrictive dietary patterns without consulting a doctor or nutritionist. Doctors are limited by restricted evidence for specific dietary approaches, lack adequate nutritional knowledge, and are constrained by the time they can dedicate to individual patients.

Certain dietary components, prevalent in the Western dietary pattern, such as highly processed foods, trans-fatty acids, refined sugars, and increased red meat intake, have been identified as factors associated with the onset and worsening of bowel diseases. The dietary effect is achieved by restricting, adding, or changing the ratio of certain food groups or specific dietary supplements, which impacts the intestinal mucosa, gut permeability, and microbiota composition. It is precisely the microbiota changes induced by dietary interventions that are the probable mechanism of effect on disease activity, as has already been shown in several studies, as well as through the use of probiotics and fecal transplantation. The literature recognizes that conducting dietary interventions within clinical trials is challenging, resulting in a small number of publications on the topic, most of which involve small sample sizes and retrospective study designs.

Extensive literature data exist on the favorable effects of the Mediterranean Diet (MD) on numerous diseases and conditions. According to the results of a recent meta-analysis of the human microbiome on a Mediterranean diet, a favorable influence on the diversity and abundance of anti-inflammatory bacterial strains has been shown compared to the microbiota of individuals with inflammatory bowel disease or colorectal cancer. The authors conclude that modulation of the gut microbiota through diet plays a role in the prevention of colon diseases.

The Mediterranean diet has proven to be one dietary approach that can positively impact individuals suffering from ulcerative colitis. To date, several studies have explored the impact of MD on UC activity with favorable outcomes. However, in all cases, these involved very small numbers of patients with retrospective study designs and disease activity assessed solely based on symptoms, without objective evaluation of the response to intervention. A study by Huskey et al. on 28 UC patients in remission on stable therapy, randomized to a Mediterranean eating style or a usual Canadian diet, showed improvement in intestinal symptoms after 12 weeks of dietary intervention with good dietary adherence. A recent prospective randomized study on 66 UC patients demonstrated a favorable effect of a combination of fecal transplantation and an anti-inflammatory diet compared to standard treatment for inducing and maintaining disease remission.

The MD is based on a traditional dietary pattern characteristic of Mediterranean countries. Its key features include: increased intake of fruits and vegetables (providing antioxidants, vitamins, and minerals), olive oil as the main fat source (rich in monounsaturated fatty acids), whole grains (rich in fiber for a positive balance of intestinal microflora), along with limited red meat intake compared to poultry and fish, and moderate consumption of dairy products.

The dietary intake of carbohydrates and their impact on human health has been widely researched in numerous indications, including inflammatory bowel diseases. According to meta-analyses, a high intake of carbohydrates has not been shown to increase the risk of developing UC, but it's important to note that most of these studies include dietary fiber in the total carbohydrate content. The beneficial effect of dietary fiber is recognized in modifying the gut microbiota, which can prevent the onset of UC and positively influence the maintenance of disease remission. A newer study by Fritsch et al. showed a favorable impact and good tolerance of a high-fiber diet in 17 patients with UC in disease remission. A recent systematic analysis indicated that a gluten-free diet and a low-FODMAP diet favorably affect the quality of life of UC patients, but not necessarily clinically significant outcomes. Reduced carbohydrate intake aimed at achieving ketosis for an anti-inflammatory effect is a subject of intense study in recent years, especially in neurological diseases and rheumatology, but it has not been adequately investigated in UC.

The Simple Clinical Colitis Activity Index (SCCAI) is used in numerous studies to assess the clinical activity of UC. Intestinal ultrasound is an established and increasingly widespread method for monitoring UC patients in clinical practice. The main ultrasound characteristics of the intestine during an inflammatory process are bowel wall thickness, bowel wall stratification, presence of Doppler signal in the wall, and presence of inflammatory reaction in the surrounding mesenteric fat tissue. Fecal calprotectin is an established monitoring method in inflammatory bowel diseases with high specificity and sensitivity for assessing disease activity