A research team from the University of Illinois at Urbana Champaign and the University of California San Diego investigated differences in the fecal microbiota in healthy adults based on compliance with the Dietary Guidelines for Americans. The study, published in The Journal of Nutrition, provides evidence that greater compliance with the Dietary Guidelines supports the gut microbiota.
Diet affects health and influences the microbiota, the trillions of microorganisms living in the gastrointestinal tract. Although extensive studies have focused on nutrient-specific effects on the gut microbiota, there is a need for diet-microbiome research. This information is critical to better understand the influence of collective food intake on the gut microbiota, which can generate translatable nutritional recommendations to accommodate a wide range of dietary needs and preferences.
To bridge this knowledge gap, Holscher and colleagues conducted a cross-sectional analysis of microbiota and food frequency data in a subset of adults participating in the American Gut Project. The cohort was comprised of 432 healthy adults between 18-60 years of age. The Healthy Eating Index (HEI)-2015, a validated measure of compliance with key Dietary Guidelines recommendations, was used to investigate the associations between habitual diet and fecal microbiota composition. The HEI-2015 is comprised of 13 components categorized into two groups: adequacy components and moderation components. Adequacy components (total fruits, whole fruits, total vegetables, greens and beans, whole grains, dairy, total protein, seafood and plant proteins, and unsaturated fatty acids) are encouraged by the Dietary Guidelines for Americans. Higher HEI-2015 scores in the adequacy category correspond to greater consumption of these foods. On the other hand, moderation components are dietary components with recommended limits to consumption, and higher scores in this category reflect a lower intake level. The cohort was divided into tertiles based on these HEI-2015 scores, and differences in microbiota abundances and diversity were compared between high and low scorers.
The mean HEI-2015 total score for low-scoring adults (58.1) was comparable with an average American adult (56.7). Those with high HEI-2015 total scores, as well as high total vegetable, greens and beans, whole grains, and dairy component scores had greater microbial diversity than those with low scores. High scorers in the fatty acid component had lower microbial diversity than low scorers. Adults in the high-scoring tertiles for HEI-2015 total score, as well as the vegetable, fruit, and grain components, had more plant carbohydrate-metabolizing microbes.
The primary finding of this study suggests that adults with greater compliance to the Dietary Guidelines have higher diversity in their fecal microbiota and a greater abundance of bacteria capable of metabolizing complex carbohydrates, providing evidence on how Dietary Guidelines support the gut microbiota. In a companion commentary, Johnson (University of Minnesota School of Public Health) expands on the strengths and limitations of using the Healthy Eating Index and the need to develop a dietary index that can fully capture the effect of dietary patterns on the microbiota.
References
Baldeon AD, McDonald D, Gonzalez A, Knight R, Holscher HD. Diet Quality and the Fecal Microbiota in adults in the American Gut Project. The Journal of Nutrition, Volume 153, Issue 7, July 2023, Pages 2004-2015, doi.org/10.1016/j.tjnut.2023.02.018.
Johnson AJ. Connecting the Healthy Eating Index With Microbiota Diversity. The Journal of Nutrition, Volume 153, Issue 7, July 2023, Pages 1846-1847, doi.org/10.1016/j.tjnut.2023.05.013.
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