Introduction
Dietary fiber is widely recognized as an important component of a healthy diet, yet it is not typically classified as an essential nutrient. In this episode, Dr. Andrew Reynolds explores whether that distinction still holds, arguing that the traditional criteria used to define essentiality may be outdated when applied to modern nutrition science.
The discussion moves beyond simply acknowledging the benefits of fiber and instead examines whether it meets the foundational requirements of an essential nutrient. This includes considering its physiological roles, the body’s inability to synthesize it in sufficient quantities, and whether low intake leads to a meaningful and reversible dysfunction.
Drawing on evidence from prospective cohort studies, randomized controlled trials, and mechanistic research, Reynolds outlines the strength of the evidence linking higher fiber intakes to reduced risk of cardiovascular disease, type 2 diabetes, colorectal cancer, and premature mortality.
- [03:50]Interview starts
- [05:53]Understanding essentiality
- [09:26]Could there be a deficiency-state for fiber?
- [15:38]What are fiber guidelines based on?
- [23:52]Fiber and chronic disease risk: dose-response
- [28:59]Different types of fiber
- [37:21]Fermentation and SCFAs
- [42:55]Research priorities ahead
- [50:04]Low fiber health risks
- [58:02]Key Ideas segment (Premium-only)
Related resources
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- Reynolds et al., 2026 – Dietary fibre as an essential nutrient:
- Reynolds et al., 2019 – Carbohydrate quality and human health: a series of systematic reviews and meta-analyses
- Episode 482: Carbohydrate Quality & Health – Andrew Reynolds, PhD
Guest Information
Click through to your app of choice to listen and subscribe:
He is interested in lifestyle risk factors such as what we eat and when we move, and health outcomes such as type 2 diabetes and heart disease. He works with both randomised controlled trials in non-communicable disease management and meta analyses in non-communicable disease prevention and management.
Danny Lennon has a master’s degree (MSc.) in Nutritional Sciences from University College Cork, and he is the founder of Sigma Nutrition.
Danny is currently a member of the Advisory Board of the Sports Nutrition Association, the global regulatory body responsible for the standardisation of best practice in the sports nutrition profession.
Useful Terminology for this Episode
- Essential nutrient: A nutrient generally considered necessary for normal physiological function, not produced by the body in sufficient amounts, and associated with a deficiency state when absent or inadequate.
- Gut dysbiosis: A disturbed gut microbial environment characterized by impaired density, diversity, or function of the microbiome, often discussed as a potential consequence of low fiber intake.
- Short-chain fatty acids (SCFAs): Metabolites produced when gut microbes ferment dietary fiber, especially acetate, propionate, and butyrate. They are thought to contribute to energy metabolism, gut integrity, immune signaling, and several downstream health effects.
- Dose-response relationship: A pattern in which changes in intake are associated with graded changes in risk or benefit. In nutrition science, dose-response evidence strengthens causal inference beyond simple high-versus-low comparisons.
- Viscous fiber: A type of fiber that forms a gel-like consistency in the gut and can slow digestion, alter bile acid handling, and improve blood lipid and glycemic responses.
- Degree of polymerization (DP): A way of describing how many monomer units a carbohydrate contains. In fiber definitions, this matters because some jurisdictions include shorter-chain oligosaccharides in the definition of dietary fiber, while others historically focused on longer-chain carbohydrates.
- Inherent fiber: Fiber that occurs naturally within foods.
- Extracted fiber: Fiber isolated from foods and added elsewhere.
- Synthetic fiber: Fiber manufactured and then added to foods.
Why Reconsider Fiber as an Essential Nutrient?
- Fiber is widely recognized as beneficial, yet it is still typically described as non-essential.
