Diet is an important determinant of health and consequently is often implicated in the development of disease, particularly gastrointestinal (GI) diseases, given the high prevalence of meal-related symptoms. The mechanisms underlying diet-driven pathophysiology are not well understood, but recent studies suggest that gut microbiota may mediate the effect of diet on GI physiology. In this review, we focus primarily on two distinct GI diseases where the role of diet has been best studied: irritable bowel syndrome and inflammatory bowel disease. We discuss how the concurrent and sequential utilization of dietary nutrients by the host and gut microbiota determines the eventual bioactive metabolite profiles in the gut and the biological effect of these metabolites on GI physiology. We highlight several concepts that can be gleaned from these findings, such as how distinct effects of an individual metabolite can influence diverse GI diseases, the effect of similar dietary interventions on multiple disease states, and the need for extensive phenotyping and data collection to help make personalized diet recommendations. Expected final online publication date for the Annual Review of Nutrition, Volume 43 is August 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Objectives Young adults tend to consume western diets with low microbe-accessible carbohydrates (MACs), which are fermentable carbohydrates that may reduce the risk of developing non-communicable diseases. The importance of dietary fiber (only one type of MAC) in the prevention of chronic diseases led to recommendations for increasing fiber intake. However, a reference to other MACs such as resistant starches, non-starch polysaccharides, polyols (lactitol, sorbitol, etc.), and oligosaccharides (fructo-oligosaccharides, etc.) is still lacking and their relationship with diet quality is far less understood. The healthy eating index (HEI) score is a measure of diet quality, independent of quantity, and is useful to assess compliance with U.S. Dietary Guidelines for Americans. The primary aim of this study was to determine the MACs consumption in healthy US college students and their association with dietary quality as indicated by the HEI-2015. Methods For this cross-sectional study, data were collected from consenting students (≥ 18years old) in an introductory nutrition course (n = 592, age (mean ± standard deviation) 19.5 ± 3.5; 83.7% white; 78.4% female). Dietary intake was measured via a web-based dietary history questionnaire (DHQ-II), which is able to quantify the consumption of MAC's and subclasses such as polyols and soluble dietary fibers. DHQ website provided step by step instructions to calculate HEI in SAS (SAS enterprise guide 7.4). Linear regression was run to determine the association between the average daily intake of MACs and the HEI-2015 score. Results Average MAC intake was 7.7 ± 4.4 grams with most of the amounts coming from soluble dietary fibers (6.6 ± 3.8). The mean HEI-score of this population was 64.9 ± 10.8. Average daily consumption of MAC was significantly associated with HEI score, F(1,590) = 65.22, P = 0.000, accounting for 10% of the variation in HEI-score with adjusted R2 = 9.8%, a medium-size effect according to Cohen (1988). An extra gram of daily average intake of MAC led to a 0.78 (95% CI, 0.59 to 0.97) increase in HEI-score. Conclusions MAC intake was associated with an increase in HEI-2015 score; however, the total MAC intake was low in this population of college students. Therefore, more efforts are needed to increase the consumption of MACs not just dietary fibers in college students. Funding Sources None.

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