A Perspective on the Complexity of Dietary Fiber Structures and Their Potential Effect on the Gut Microbiota

• The energy that is required for colonic bacterial growth is fulfilled mostly by dietary compounds, particularly dietary fibers.
• Dietary fiber has a greater range of structures than is generally appreciated.
• It is proposed that dietary fiber be viewed as a vast array of discrete structures that align with encoded gene clusters in bacterial genomes.
• Using this concept, the article encourages the building of a framework of information to manipulate the colon microbiota in a predicted way for improved health.

Even though there are many factors that determine the human colon microbiota composition, diet is an important one because most microorganisms in the colon obtain energy for their growth by degrading complex dietary compounds, particularly dietary fibers. While fiber carbohydrates that escape digestion in the upper gastrointestinal tract are recognized to have a range of structures, the vastness in number of chemical structures from the perspective of the bacteria is not well appreciated. In this article, we introduce the concept of “discrete structure” that is defined as a unique chemical structure, often within a fiber molecule, which aligns with encoded gene clusters in bacterial genomes. The multitude of discrete structures originates from the array of different fiber types coupled with structural variations within types due to genotype and growing environment, anatomical parts of the grain or plant, discrete regions within polymers, and size of oligosaccharides and small polysaccharides. These thousands of discrete structures conceivably could be used to favor bacteria in the competitive colon environment. A global framework needs to be developed to better understand how dietary fibers can be used to obtain predicted changes in microbiota composition for improved health. This will require a multi-disciplinary effort that includes biological scientists, clinicians, and carbohydrate specialists.

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