Sigma Nutrition Radio

We take a look at critical thinking in science and healthcare, examining how we often fall prey to cognitive biases, emotional reasoning, and flawed thinking. Drawing from six different experts in their respective fields, the episode explores why we sometimes believe we are being rational when in fact our conclusions aren't truly evidence-based. The discussion spans what genuine evidence-based practice means, how domain expertise matters, and how factors like identity, beliefs, and emotions can derail objective reasoning.

• [02:56] Dr. David Nunan on evidence-based medicine
• [15:30] Dr. John Kiely on translating research into practice
• [26:10] Dr. Gil Carvallo on emotion and decision making
• [30:10] Dr. David Robert Grimes on webs of belief
• [37:18] Dr. Matthew Facciani identity and belief formation
• [42:31] Dr. Alan Flanagan on domain-specific expertise in nutrition science

How should we think about diets that claim to optimise both human and planetary health? Can a single "reference diet" really balance the complex trade-offs between nutrition adequacy, chronic disease prevention, and environmental sustainability?

These questions have gained renewed attention with the release of the 2025 update to the EAT-Lancet Planetary Health Diet. The original 2019 report proposed a mostly plant-based dietary pattern designed to improve population health while staying within planetary boundaries. But since then, new data have emerged—on nutrient requirements, disease risk, and environmental modelling—that complicate many of the original assumptions.

What does the updated evidence actually say about the health impacts of eating in line with this framework? How have the environmental projections changed? And what do these evolving targets mean for individuals, policymakers, and researchers trying to translate broad sustainability goals into practical dietary guidance?

These are some of the questions explored in this episode of Sigma Nutrition, which examines the 2025 EAT-Lancet update, its scientific foundations, and what it reveals about the intersection of nutrition, health, and planetary sustainability.

• [01:46] Focus on the 2025 EAT-Lancet report
• [02:27] Overview of the Planetary Health Diet
• [03:13] Comparing 2019 and 2025 reports
• [03:40] Dietary recommendations and nutrient targets
• [04:14] Health and environmental impacts
• [09:12] Scoring methods and dietary patterns
• [27:00] Mortality and chronic disease outcomes
• [40:01] Type 2 diabetes
• [44:13] Neuroimaging and cognitive outcomes
• [49:48] Conclusions and practical implications
• [58:55] Key ideas segment (Premium-only)

Ultra-processed foods have become central to the way we eat and to many of the challenges we face in public health nutrition. They dominate supermarket shelves, shape population diets, and often appear as the prime suspect in rising obesity and metabolic disease rates. But beyond the label itself, what exactly makes these foods problematic? Is it their nutrient composition, their texture and palatability, the rate at which we consume them, or the broader environments that make them so accessible and appealing?

The debate around ultra-processed foods sits at the intersection of metabolic science, behaviour, and policy. It raises uncomfortable questions about how food systems evolved to prioritise convenience and profit, and what it might take to meaningfully change that trajectory.

In this episode, Dr. Kevin Hall joins the podcast to examine the evidence from controlled feeding studies and population research, exploring what we really know about ultra-processed foods, overeating, and how we might begin to fix the food environment.

• [04:24] Dr. Hall's background and career
• [06:47] Ultra processed foods and health
• [15:10] Mechanisms behind ultra processed foods
• [27:00] Healthy ultra processed foods: a possibility?
• [30:43] Minimizing ultra processed foods in different cultures
• [33:03] Policy and regulation for better food quality
• [44:26] The importance of pilot studies in policy implementation
• [49:10] Future of food and sustainable diets
• [51:50] Key ideas segment (Premium-only)

GLP-1 receptor agonists have emerged as a groundbreaking tool in obesity treatment. In this episode, Dr. Spencer Nadolsky (an obesity specialist) explains how these medications are now yielding unprecedented weight loss outcomes in people with obesity.

The discussion centers on GLP-1 agonist drugs like semaglutide and tirzepatide: how they work, how much weight loss they can produce, and why they represent a paradigm shift in obesity management.

Importantly, the conversation addresses practical aspects of using these drugs, including managing their side effects and optimizing patients' diet and lifestyle while on therapy.

This topic is of great significance to nutrition science, clinical practice, and public health. Obesity is a chronic, relapsing condition that has proven difficult to treat with lifestyle changes alone. The advent of GLP-1 agonists offers new hope by inducing weight loss levels previously seen only with surgical interventions.

Understanding these medications is crucial for healthcare professionals: it enables evidence-based prescribing, proper patient counseling on diet and side effects, and integration of medication with lifestyle interventions.

Discussing safety and long-term use is vital, as millions more patients might use these drugs in coming years. From a public health perspective, GLP-1 agonists prompt debates about access and cost, given their high price and life-changing potential.

• [03:25] Conversation with Dr. Spencer Nadolsky begins
• [05:24] Mechanism and types of GLP-1 medications
• [07:55] Efficacy and weight loss results
• [16:53] Common side effects and management
• [22:57] Muscle loss concerns and clinical insights
• [28:09] Addressing nutritional concerns with GLP-1 medications
• [29:38] Exploring potential benefits beyond weight loss
• [33:48] Marketing and misconceptions around GLP-1
• [36:59] Public health and accessibility issues
• [43:25] Future research
• [46:16] Key ideas segment (Premium-only)