#603: Should Dietary Fiber Be Considered Essential? – Andrew Reynolds, PhD

In this episode of Sigma Nutrition Radio, host Danny Lennon welcomes back Dr. Andrew Reynolds, an associate professor at the University of Otago, to discuss his recent comment piece in Nature Food titled 'Dietary Fiber as an Essential Nutrient.' Reynolds argues that despite not meeting traditional criteria for essentiality—such as a clearly defined deficiency disease—dietary fiber should be reclassified as essential due to its critical role in maintaining a healthy gut microbiome. He posits that an inadequate or dysregulated gut microbiome, which can be reversed with increased fiber intake, constitutes a modern deficiency state. The discussion delves into the evidence behind current fiber recommendations (typically 25–30 grams per day), the strength of both observational and randomized controlled trial data, and the challenge of dose-response relationships. Reynolds emphasizes that the greatest health benefits occur when people move from very low to moderate fiber intakes, even if higher intakes offer diminishing returns. He also addresses the complexity of fiber subtypes, the role of the microbiome in producing short-chain fatty acids, and the importance of gradual increases in fiber to avoid gastrointestinal discomfort. The episode concludes with a call for redefining essentiality in modern nutritional science, with potential public health benefits including increased policy prioritization, food reformulation, and improved dietary messaging. Key takeaways include: 1) Increasing fiber intake from low to moderate levels offers the most significant health benefits, especially for reducing risk of heart disease, type 2 diabetes, and colorectal cancer; 2) The gut microbiome's health—measured by density, diversity, and functionality—may serve as a valid modern deficiency state for fiber; 3) Fiber should be viewed as a functional nutrient rather than a single entity, with multiple types contributing to health through different mechanisms; 4) Gradual increases in fiber are essential to avoid bloating and gas; 5) Reclassifying fiber as essential could drive public health policy, food industry reformulation, and better consumer understanding. The overall sentiment is strongly positive, emphasizing the transformative potential of rethinking fiber in nutritional science.