Sigma Nutrition Radio

Fasting, nutrient timing, chrono-nutrition, and continuous glucose monitoring are all topics that have generated substantial interest, but they are also areas where exaggerated claims can easily outpace the underlying evidence.
In many cases, tentative hypotheses are presented as if they were already well-established conclusions, despite the fact that the research base is often more mixed and context-dependent than popular narratives imply. It is one thing for an idea to appear biologically coherent. It is another for that idea to translate into meaningful, reliable effects in real-world interventions.
In this episode, Professor James Betts discusses how to think clearly about these topics, why common errors in interpretation can lead to overstated conclusions, and what is required to properly evaluate whether an observed effect reflects a true intervention effect rather than baseline differences, inappropriate comparisons, within-group changes, or mechanistic signals being mistaken for meaningful health outcomes.
Timestamps:
[04:24] Background into Prof. Betts' research
[07:28] Evidence in fasting research over past 5-6 years
[10:15] Hype vs evidence in intermittent fasting
[16:44] Spotting spin in study conclusions
[17:31] Common statistical red flags
[24:45] Methods matter in fasting trials
[31:10] Exercise nutrient timing
[38:32] CGMs what they measure, misuse and patterns
[53:59] Key ideas (premium-only)
 
Links:
Go to episode page & resources (study links, bio, etc.)
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How should we decide what counts as trustworthy evidence? Scientific rigor is not a single characteristic of a study, but a chain of decisions made from the moment a question is conceived to the point at which findings are communicated to the public.
Errors can occur at every stage: the question may be ill-posed, the design may be incapable of answering it, the measurements may be weak, the analysis may be inappropriate, the interpretation may overreach, and the public-facing communication may become distorted.
In this episode, Dr. David Allison, PhD discusses the deeper methodological issues that shape the field's conclusions. The discussion moves from the philosophy of scientific inquiry to the practical realities of study design, statistical analysis, interpretation, and dissemination.
Timestamps:
[03:30] Interview start
[06:17] What is true scientific rigor?
[10:06] Study design and analysis problems in nutrition
[12:56] The DINS error
[14:14] Conflation of heterogeneity in response vs. in outcomes
[17:31] Misunderstanding of p-values and hypothesis testing
[27:01] Incorrect labelling of "responders" and "non-responders"
[34:49] Errors related to analysis of secondary outcomes
[45:01] How can nutrition science improve as a field?
[51:30] Key ideas segment (Premium-only)
Links:
Go to episode page (with list of episode resources)
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Enroll in the next cohort of our Applied Nutrition Literacy course

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