Mediterranean Diet and the Gut Microbiome

Impact of the Mediterranean Diet on the Gut Microbiome and Symptoms of Diarrhea-Predominant Irritable Bowel Syndrome

This study will evaluate the impact of a Mediterranean-style diet on microbiome diversity compared to a typical American diet. The study will observe the microbiome composition comparisons in healthy volunteers as well as in patients with Irritable Bowel Syndrome with Diarrhea (IBS-D) to see if the consumption of a Mediterranean-style diet has a positive effect on improving symptoms of IBS-D.

Irritable bowel syndrome (IBS) is the most prevalent and well-studied functional gastrointestinal disorder. While IBS has no direct mortality, it does compromise quality of life, incurs morbidity, and has a substantial economic impact on society. The gut microbiome may play a significant role in the pathogenesis of IBS. Even though the exact mechanisms underlying this relationship have not been presented, it is suggested that certain microorganisms may increase gut permeability, activate the mucosal immune response, increase visceral sensitivity and alter intestinal motility via a bidirectional brain-gut interaction. Recent studies suggest that the salutary impact of the Mediterranean diet may be due to its effects on the composition of the gut microbiome. In a recent cohort study in Italy, subjects who adhered most closely to a classical Mediterranean diet had more favorable bacterial enterotypes (e.g., Prevotella) in their stool, as well as higher levels of short-chain fatty acids - which are essential for colonic function. Studies have also showed that diet alters the predominant microbiome enterotypes and that microbiome composition can change quickly, within 24 hours, after a dietary intervention. Therefore, consumption of a Mediterranean diet may ameliorate the gut dysbiosis associated with IBS-D.

The study will have two phases, Phase 1 will study healthy subjects, who will follow a typical American diet for 2 weeks, and then cross-over to a Mediterranean-style diet for 2 weeks. Phase 2 will study subjects who have IBS-D. As above, they will first eat a typical American diet for 2 weeks, and then cross-over to a Mediterranean-style diet.

Healthy volunteers will eat a typical American diet for 2 weeks and then eat a Mediterranean-style diet for 2 weeks.

Participants with IBS will eat a typical American diet for 2 weeks and then eat a Mediterranean-style diet for 2 weeks

According to National Health and Nutritional Examination Survey (NHANES) data, the nutritional composition of the baseline typical American diet is 50%Carbohydrates, 15% Protein, 35% Fat, >11% Saturated Fatty Acids, <12% Monounsaturated Fatty Acids, and >8% Polyunsaturated Fatty Acids. Participants will receive 3 meals and 1 snack for each day during the study period.

The nutritional composition of the baseline typical Mediterranean-style diet is 46% Carbohydrates/Alcohol (red wine will be included in the Mediterranean diet only), 17% Protein, 32% Fat, <7% Saturated Fatty Acids, >18% Monounsaturated Fatty Acids and <5% Polyunsaturated Fatty Acids. Participants will receive 3 meals and 1 snack for each day during the study period.

Fecal microbiota diversity and enterotypes will be determined through bacterial 16S rRNA gene sequences on stool samples collected from the healthy volunteer participants in phase 1.The data will initially be analyzed by calculating descriptive statistics and plotting to examine for potential outliers and the necessity for data transformation.

Fecal microbiota diversity and enterotypes will be determined through bacterial 16S rRNA gene sequences on stool samples and rectal biopsies performed on the subjects with IBS-D in phase 2.The data will initially be analyzed by calculating descriptive statistics and plotting to examine for potential outliers and the necessity for data transformation.

A plasma inflammatory marker that will be analyzed is the Erythrocyte sedimentation rate (ESR). Data will be analyzed in comparison of time points Baseline, 2 weeks and 4 weeks.

A plasma inflammatory marker that will be analyzed is C-reactive protein (CRP). The CRP is measured through a blood test. A CRP level of 10mg/L or lower is considered to be normal. A higher CRP indicates that their is inflammation in the body.Data will be analyzed in comparison of time points Baseline, 2 weeks and 4 weeks.

The IBS Severity Scoring System is a validated measure to assess the severity of IBS symptoms, and can help monitor response to treatment. Each of the 5 questions generates a score from 0-100 points with a maximum total score of 500 points. Mild IBS=75-174 points, moderate IBS=175-299 points, and severe IBS=300 points of more.Data will be analyzed in comparison of time points Baseline, 2 weeks and 4 weeks.

Hospital Anxiety and Depression Scores (HADS) is a self assessment scale designed to detect states of depression, anxiety, and emotional distress in patients who are being treated for a clinical problem. The scale has 14 questions that are scored on a scale of 0-3, with 3 indicating higher symptom frequencies. Scores for each subscale (anxiety and depression) range from 0 to 21 with scores categorized as follows: normal 0-7, mild 8-10, moderate 11-14, and severe 15-21. Scores for the entire scale (emotional distress) range from 0 to 42, with higher scores indicating more distress.Data will be analyzed in comparison of time points Baseline, 2 weeks and 4 weeks.

Inclusion Criteria: must be willing to eat pre-prepared foods for 4 weeks subjects must have no medical, religious, or cultural dietary restrictions that would preclude their eating a Mediterranean diet. Phase 2 subjects- must have diagnosis of IBS based on Rome III criteria and have diarrhea-predominant disease, defined as >50% of bowel movements characterized as diarrhea Exclusion Criteria: history of gastrointestinal disease, including celiac disease, inflammatory bowel disease, or lactose intolerance diabetes mellitus congestive heart failure coronary artery disease chronic liver disease or end stage renal disease pregnancy or breastfeeding trainees under the direct supervision of the PI and patients receiving direct ongoing medical care from the PI or Co-I will not be enrolled as subjects in this study

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