Sigma Nutrition Radio

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explores whether that distinction still holds, arguing that the traditional criteria used to define essentiality may be outdated when applied to modern nutrition science.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. 
Reynolds presents a compelling case that fiber may play a fundamental role in maintaining normal physiological function and therefore warrants reconsideration within the framework of essential nutrients.
Timestamps:
[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

Avoidant/Restrictive Food Intake Disorder (ARFID) is an eating disorder diagnosis characterized by a persistent restriction or avoidance of food intake that results in clinically significant consequences (medical, nutritional, and/or psychosocial), but without the weight- and shape-driven psychopathology typical of anorexia nervosa and bulimia nervosa.
In this episode, Megan Hellner and Katherine Hill outline how ARFID presents across the lifespan, why it is frequently missed in routine healthcare, and what an evidence-informed assessment and treatment pathway can look like in practice.
A central theme is that ARFID is not synonymous with "picky eating" and not confined to any one body size. Patients may present at any point on the weight chart, including those who are weight-stable or in larger bodies, and the condition can begin in early childhood and persist into adulthood.
The episode also highlights ARFID in athletes and physically active people, where restricted dietary variety and/or low intake can contribute to low energy availability and RED-S-like presentations, sometimes without an obvious intent to lose weight.
Timestamps
[03:48] Interview start
[06:23] What is ARFID? DSM-5 definition vs "picky eating"
[09:36] Clinical red flags: when restriction becomes a disorder
[11:37] ARFID isn't always underweight: missed cases & diagnostic pitfalls
[16:46] ARFID presentation profiles: low interest, sensory sensitivity, fear
[18:59] Comorbidities & nutrition consequences
[25:16] Evidence-based ARFID treatment
[29:16] How to expand foods without pressure
[32:28] Weight restoration, stabilization, and long-term maintenance
[35:44] What research still needs
[38:16] Differential diagnosis & referral
Links/Resources
Go to episode page (with links to papers and ARFID resources)
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This episode examines what we actually know (and importantly, what we do not know) about diet in relation to gallstones and gallbladder conditions. Much of the public-facing guidance around gallstones focuses on "avoiding fatty foods", yet Dr. Angela Madden explains that this long-standing practice sits on surprisingly weak direct evidence, particularly when judged against the standards typically expected for clinical dietary recommendations.
A central theme is the need to separate two distinct questions: dietary factors that influence the risk of developing gallstones (prevention), versus dietary strategies intended to reduce symptoms or complications once gallstones exist (management). While the prevention literature suggests plausible, consistent associations with overall diet quality and lifestyle factors, the specific question of prescribing a low-fat diet to manage symptomatic gallstones lacks robust randomized trial evidence.
Dr Angela Madden is a clinical researcher in nutrition and dietetics at the University of Hertfordshire, where she established and led the nutrition and dietetics subject group and now focuses her research on improving nutritional assessment, dietary interventions, and patient-centred outcomes in clinical and public health settings.
Timestamps
[02:09] Discussion with Dr. Angela Madden begins
[06:53] Understanding the gallbladder
[08:08] Gallbladder disorders and their prevalence
[13:42] Risk factors and pathophysiology
[22:15] Dietary factors and gallstone formation
[27:20] Exploring dietary fat and gallstones
[34:09] Broader dietary considerations
[45:44] Practical dietary recommendations
Related Resources
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Dr. Madden's univeristy page
Cochrane Review: Madden et al., 2024 – Modified dietary fat intake for treatment of gallstone disease in people of any age
Related episode: 513: Kidney Stones & Diet – Deepa Kariyawasam, RD

In this episode, Danny answers questions submitted by Premium subscribers.
Questions Answered in This Episode:
[00:05:13] Is eating too early (relative to chronotype) metabolically problematic?
[00:16:55] Can plant-based diets reverse cardiovascular disease?
[00:32:54] Are multivitamins useful insurance, or a waste with a good diet?
[00:44:56] Does coevolution with foods determine human compatibility and benefit?
[00:56:25] How should consumers choose supplement formulations and brands?
[01:04:46] Folate vs folic acid: differences and best choice for women of childbearing age?
[01:12:37] How reliable is omega-3 content in farmed salmon, especially imported frozen salmon?
[01:19:18] How accurate are food labels for metabolizable energy and absorption, especially across processing levels?
[01:23:58] Protein needs in breastfeeding and general rehabilitation (non-sport injury)?
To listen to the full episode, subscribe to Sigma Nutrition Premium.
Related Resources
Go to episode page (with full resource list)
Subscribe to Sigma Nutrition Premium
Resources for this episode: Eckel et al., 2015 – Morning Circadian Misalignment during Short Sleep Duration Impacts Insulin Sensitivity
Stothard et al., 2020 – Early Morning Food Intake as a Risk Factor for Metabolic Dysregulation
Ep. #470: Melatonin, Meal Timing & Glucose Tolerance
Ep. #579: Is Your Chronotype Hard-Wired or Modifiable?
Article: A Plant Based Diet Reverses Heart Disease: True or False?

"The more we learn about the world, and the deeper our learning, the more conscious, specific, and articulate will be our knowledge of what we do not know, our knowledge of our ignorance. For this, indeed, is the main source of our ignorance — the fact that our knowledge can be only finite, while our ignorance must necessarily be infinite." – Karl Popper
To mark Sigma Nutrition's milestone 600th episode (and 12-year anniversary), Danny and Alan examine several areas in which their views have changed, softened, strengthened, or remained stable over the lifespan of the podcast.
The discussion is therefore not only about nutrition itself, but also about the process of scientific reasoning: how positions are formed, what type of evidence can shift them, and why changing one's mind is often a sign of better thinking rather than inconsistency.
The episode therefore serves as both a review of several specific nutrition controversies and a lesson in scientific epistemology. They discuss topics such as red meat, protein, dietary cholesterol, omega-3s, flavonoids, and sodium.
Timestamps
[11:04] Time-restricted eating
[19:32] Protein intake, quality & dosing
[35:04] Cocoa flavanols and cognition
[51:38] Unprocessed red meat
[01:05:23] Omega-3 supplementation
[01:23:10] Dietary cholesterol
[01:44:41] Sodium J-curve myth
[01:53:41] Energy balance model
Links
Go to episode page (with study links & resources)
Join the Sigma email newsletter for free
Subscribe to Sigma Nutrition Premium
Enroll in the next cohort of our Applied Nutrition Literacy course