Energy expenditure is one of the most fundamental yet often misunderstood aspects of human physiology. A central question is whether there is a ceiling to how many calories we can burn, and what happens when activity levels approach that limit. Grasping these dynamics is essential for health professionals and researchers, as energy balance directly influences body weight regulation, metabolic health, and athletic performance.

Emerging research shows that our bodies regulate calorie burn not in a fixed manner, but through adaptation and compensation, revealing that the “calories in vs. calories out” model is far more dynamic than it may first appear.

In this episode, we revisit key insights from experts such as Dr. Herman Pontzer, Dr. Brent Ruby, Dr. Mark Hopkins, Dr. Eric Trexler, and Dr. Chris Melby. These perspectives cover how the body adapts to different levels of physical activity, the metabolic adjustments during weight loss (often called adaptive thermogenesis), and the concept of energy flux in weight maintenance.

Note: This episode is one of our Premium-exclusive episodes. To listen to the full episode, you’ll need to be a Premium subscriber and access the episode on the private Premium feed. Otherwise, you can hear a preview of the episode on the public feed of the podcast.

• [03:36] Contrained model of energy expendiure
• [12:33] What is the ceiling of human energy expenditure?
• [13:05] Reconciling energy intake and expenditure
• [13:32] Variability in metabolic rates
• [15:16] Adaptive thermogenesis and weight loss
• [18:37] Metabolic adaptation explained
• [31:51] Energy flux and weight maintenance

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• Article: The “Calories In, Calories Out” Confusion: A Comprehensive Guide to Understanding Energy Balance
• Included episodes:
  • 208 – Herman Pontzer, PhD | Constrained Energy Expenditure Model & Evolutionary Biology of Energy Balance
  • 124 – Brent Ruby, PhD | The Human Ceiling of Energy Expenditure
  • 299 – Mark Hopkins, PhD | Compensatory Eating & Activity Energy Expenditure
  • 377 – Herman Pontzer, PhD | Metabolism, Mitochondria & Measuring Energy Expenditure
  • 484 – Eric Trexler, PhD | Is Metabolic Adaptation an Illusion?
  • 318 – Chris Melby, DrPH | Impact of Energy Flux on Weight Management

Recently a new trial was published in Nature Medicine comparing the effect of ultra-processed versus minimally processed diets. Specifically, the UPDATE trial compared these two diets in the context of a healthy dietary pattern (in line with the UK’s EatWell Guide).

This eight-week randomized, crossover trial generated a lot of discussion and was largely seen as being a really useful addition to the evidence base, and providing answers to some previously unexamined questions.

In this episode the study’s lead author, Dr. Samuel Dicken, explains the background context for the UPDATE trial, provides an insight into its execution, and puts some of the results in context. There is also a discussion about the current state of evidence more broadly and the leading hypotheses around the mechanisms that drive the observations seen with consuming ultra-processed foods.

This episode is particularly noteworthy because it provides fresh evidence on an important question: does following dietary guidelines with minimally processed foods confer extra benefits over following the same guidelines with ultra-processed foods?

• [02:48] Interview with Dr. Samuel Dicken
• [03:08] Background and research interests of Dr. Samuel Dicken
• [04:31] Details of the update trial
• [09:48] Trial design and methodology
• [15:45] Results and findings of the update trial
• [18:46] Secondary outcomes and craving control
• [25:43] Hypotheses and mechanisms behind UPF effects
• [40:28] Policy implications and future research directions

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• Study: Dicken et al., 2025 – Ultraprocessed or minimally processed diets following healthy dietary guidelines on weight and cardiometabolic health: a randomized, crossover trial
• LinkedIn: Samuel Dicken
• X: @SamuelDickenUK

In this episode, Dr. Matthew Facciani explores how social psychology influences health beliefs and the spread of misinformation. The conversation delves into why people adopt certain nutrition or health beliefs so strongly, how identity and group membership shape our interpretation of evidence, and what makes us susceptible to false or misleading health claims.

Dr. Facciani’s interdisciplinary background (spanning neuroscience, psychology, and sociology) allows him to offer a unique evidence-informed perspective on these issues. The episode centers on understanding the social forces behind health-related attitudes and how we might improve communication and critical thinking in the face of rampant misinformation.

This topic is highly relevant for health professionals and researchers because misinformation about nutrition, health, and medicine can lead to poor decisions, vaccine hesitancy, or harmful fad diets. By understanding the psychological drivers that cause people to cling to unscientific beliefs, practitioners can better address patients’ concerns and correct false claims.

Matthew Facciani is a postdoctoral researcher at The University of Notre Dame in the Computer Science and Engineering Department. He is an interdisciplinary social scientist with a background in neuroscience and psychology and holds a PhD in sociology. His research focuses on media literacy, misinformation, social networks, political polarization, identities, and artificial intelligence.

• [01:41] Interview start
• [06:57] The role of identities in belief formation
• [16:01] Health attitudes and political identities
• [25:28] Improving dialogue and addressing misinformation
• [31:59] Does fact-checking work?
• [35:41] Media literacy and pre-bunking
• [44:03] Optimism and pessimism for the future
• [52:28] Key ideas segment (premium-only)

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• Matthew’s book: ‘Misguided’
• Matthew’s academic publications
• Recommended episode: #365: David Robert Grimes, PhD – Conspiracy Theories & Bad Information: Why Are We Susceptible?

Dairy is often treated as a single food group, yet milk, yogurt, cheese, and butter can have very different effects on health. Some evidence links yogurt to favourable outcomes, while butter is known to raise LDL cholesterol. And then there’s the paradox of cheese: high in saturated fat, but not consistently associated with higher heart disease risk.

These complexities raise the question of whether the “dairy matrix” (the combination of nutrients and food structure) explains why not all dairy acts the same.

In this episode, Prof. Jean-Philippe Drouin-Chartier, a nutrition researcher and registered dietitian, is on the show to examine what recent trials and large population studies tell us about dairy foods and cardiometabolic health. The discussion covers blood lipids, blood pressure, glucose metabolism, and how guidelines should interpret this evolving evidence.

• [02:18] Interview start
• [09:38] Dairy consumption and type 2 diabetes
• [16:06] Dairy and cardiovascular disease
• [21:42] Dairy, blood pressure, and hypertension
• [25:56] Dietary guidelines and dairy
• [43:30] Key ideas segment (Premium-only)

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• Referenced studies linked here

They’re in our oceans, our air, our food, and now even in our bodies. Microplastics, once a distant environmental issue, have become a topic of urgent relevance in medicine, public health, and nutrition. The idea that tiny plastic particles are circulating through the food chain and accumulating in human tissues has sparked headlines, speculation, and concern. But how much of this fear is grounded in solid science? And how much is still unknown?

As the research into microplastics rapidly grows, so too does the confusion. Claims range from the plausible to the alarmist, yet the real picture is far more complex. What does current evidence actually tell us about the health implications of microplastic exposure? How do we weigh these emerging signals against the backdrop of other environmental threats we understand much better? And how should scientifically-minded practitioners think about this issue, especially when patients begin asking questions?

This is a conversation that calls for clarity, nuance, and a rigorous look at what we know versus what remains speculative. In this episode, Professor Ian Mudway, an environmental toxicologist, discusses the current scientific understanding of microplastics and human health.

• [03:31] The public’s fascination with microplastics
• [08:35] Defining microplastics and nanoplastics
• [11:35] Environmental presence of microplastics
• [14:54] Human exposure to microplastics
• [18:23] Challenges in measuring microplastics
• [21:38] Public perception vs. scientific reality
• [27:08] Challenges in microplastic research
• [29:53] Environmental impact and human health
• [33:08] Complexities of plastic additives
• [40:34] Future directions in microplastic research
• [48:09] Key ideas segment (Premium-only)

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• Gresham College YouTube lectures
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In this episode, performance nutritionist Daniel Davey discusses how his approach to elite sports nutrition has evolved over his career. Davey reflects on his decade working with top Irish teams (Dublin GAA/football and Leinster Rugby) and how stepping away from those environments led him to rethink the role of a nutrition practitioner.

The central theme is a shift from a traditional prescriptive model, where the expert provides meal plans and quick solutions, to a philosophy centered on athlete empowerment, education, and long-term habit development. Davey emphasizes that true high performance is achieved not by spoon-feeding athletes every nutrient, but by cultivating their independence, adaptability, and ownership of the process.

This episode delves into practical strategies for fostering that ownership, such as encouraging self-reflection, building a supportive “nutrition culture,” and focusing on sustainable habits over short-term fixes. This discussion is highly relevant to nutrition science and clinical practice because it addresses the often-overlooked behavioral and cultural aspects of dietary change.

Health professionals will recognize parallels to coaching clients in any setting: the importance of engaging individuals in their own nutrition planning, the value of reflective practice, and the balance between providing support and encouraging autonomy.

• [02:38] Interview start
• [07:29] Empowering athletes
• [12:36] Challenges and reflections
• [16:53] Practical applications and philosophy
• [23:33] Building sustainable habits
• [28:00] Empowering decision-making through clarity
• [30:03] The importance of consistency and planning
• [31:47] Leadership and team dynamics
• [34:38] Personal growth and overcoming challenges
• [40:27] The concept of non-negotiables
• [52:31] Key ideas segment

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• See Sigma's Recommended Resources
• Daniel Davey’s previous appearences on the podcast: go to episodes 306 and 194

In recent years “Zone 2 training” has gained immense popularity in fitness and health circles, often being proclaimed the “best” cardiovascular training for metabolic health. Zone 2 training is sustained, low-intensity exercise below the lactate threshold that is commonly employed by many elite level endurance athletes, with a variety of proposed performance benefits. This led to interest from health-conscious folks about its ability to improve markers like VO2 max and mitochondrial function, which are associated with better health outcomes and longevity.

Prof. Brendon Gurd, an exercise physiologist at Queen’s University, is the co-author of a recent review published in Sports Medicine that examined some of the claims made around zone 2 training and health in the general population.

This episode looks at whether the evidence truly supports Zone 2 as a uniquely effective training zone or if this hype has outpaced the research. These insights help professionals and individuals make evidence-based recommendations and avoid unintended negative consequences of following certain ideas.

About The Guest

Dr. Brendon Gurd is a Professor in the School of Kinesiology and Health Studies at Queen’s University, where his research focuses on exercise physiology and skeletal muscle adaptation. His work explores how different intensities and types of exercise influence mitochondrial content and function in muscle tissue, with the goal of understanding how to optimize health and performance through training.

• [03:23] Discussion with Professor Brendan Gurd
• [05:56] Zone two training: Mechanisms and misconceptions
• [10:56] Practical applications and recommendations
• [22:16] Research gaps and future directions
• [35:47] Key ideas segment (Sigma Nutrition Premium)

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• List of Sigma's Recommended Resources
• Review paper: Storoschuk et al., 2025 – Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population
• Lecture Slides: Prof. Brendon Gurd – Is Zone 2 the optimal intensity for inducing mitochondrial adaptation?