The intersection of nutrition, dermatology, and skin health is an area of growing interest, yet one that remains riddled with misinformation and oversimplified claims.

The influence of dietary patterns, specific nutrients, and lifestyle factors on conditions such as acne, eczema, psoriasis, and skin aging has been widely debated, with varying levels of evidence supporting different interventions.

While some nutritional strategies may play a role in optimizing skin health, the challenge lies in distinguishing practical, evidence-based approaches from overstated or anecdotal claims.

A significant issue in this space is the naturalistic fallacy—the belief that diet alone can replace medical treatments, or that conventional dermatological interventions should be avoided in favor of “natural” approaches. This has led to widespread vilification of certain foods, such as dairy, gluten, and sugar, despite a lack of strong supporting data.

Similarly, supplements and probiotics are often promoted with broad claims, while their actual efficacy is highly context-dependent—varying based on individual nutrient status, disease severity, and baseline dietary intake.

In this episode, Dr. Thivi Maruthappu, a consultant dermatologist and researcher in nutritional dermatology, joins Danny Lennon to explore the current state of evidence in this field.

Guest Information

Dr Thivi Maruthappu MA PhD FRCP ANutr is a consultant dermatologist, nutritionist and leading researcher. As the UK’s first and only dual-qualified dermatologist and nutritionist, her pioneering expertise bridges the gap between diet and skin health. Dr Thivi continues to work in the NHS and has her own practice based at London’s renowned Cleveland Clinic.

Dr Thivi studied Medicine at Oxford University and completed Dermatology training in London. She undertook a PhD to understand the links between our skin and internal health and this research featured in top tier scientific journals. She is one of a handful of dermatologists to have completed training in severe eczema and psoriasis during a fellowship at St John’s Institute of Dermatology, London and achieved a Certificate in Nutrition Science from Stanford Medical School, USA.

Timestamps

• [02:52] Start of interview
• [03:37] Dr. Maruthappu’s background and expertise
• [05:57] Sunscreen and skin health: myths and facts
• [12:15] Effective skincare ingredients
• [16:07] The role of nutrition in skin health
• [20:25] Dairy and skin conditions
• [24:10] Collagen supplements: do they work?
• [27:45] Probiotics for skin health
• [31:35] Research outcomes and challenges
• [35:20] Practical applications in clinical practice
• [43:05] Key ideas segment (premium-only)

Related Resources

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Dr. Maruthappu’s website

Discussions around ultra-processed foods (UPFs) and their role in public health have gained significant traction in recent years. While some advocate for categorizing and regulating these foods due to their potential negative health effects, others argue that such classifications can oversimplify the issue and detract from more actionable dietary changes.

In this episode, Dr. Duane Mellor, a registered dietitian and researcher, joins us to explore the complexities of the UPF debate. Rather than dismissing the concept outright, Dr. Mellor emphasizes the importance of nuanced discussion, bridging the gap between research findings and practical, evidence-based dietary guidance.

Throughout this conversation, we unpack the broader implications of ultra-processed foods in the food system, consider how added fat, salt, and sugar contribute to public health challenges, and explore realistic approaches for dietary improvements.

Guest Information

Dr. Duane Mellor, PhD is a registered dietitian, academic researcher and science communicator. Dr. Mellor is currently working in clinical dietetics, working to support people, families and carers living with diabetes.

Previously Dr. Mellor worked in medical education at Aston University, holding the position of Associate Dean for Public Engagement in the College of Health and Life Sciences.

After initially working in the areas of clinical trials, Dr. Mellor’s other research interests focused on improving nutrition and health by working with communities to celebrate their heritage through food and help tackle barriers resulting from societal inequalities.

Timestamps

• [03:02] Interview start
• [06:39] Understanding the NOVA classification
• [09:53] Potential pitfalls and policy implications
• [14:52] Food science and technology perspectives
• [20:47] Challenges in food classification
• [26:13] Health equity and policy considerations
• [42:31] Communication and public perception
• [50:30] Final thoughts and advice
• [51:15] Key ideas segment (Premium-only)

Related Resources

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Paper: Mellor, 2024 – The role of food science and technology in navigating the health issues of ultra-processed foods
• Go to sigmanutrition.com

In the realm of health psychology, our understanding of eating behaviors extends beyond mere physiological hunger cues. Research indicates that factors such as learned associations, cultural influences, and individual perceptions play pivotal roles in shaping our dietary choices.

Recognizing this complexity is essential for developing effective dietary interventions that move beyond simplistic recommendations, acknowledging the intricate web of cognitive, emotional, and societal factors at play.

A significant discussion within nutrition science centers on the regulation of eating patterns, particularly the balance between internal cues and external structures. While intuitive eating emphasizes responding to one’s internal hunger signals, studies suggest that these signals are often influenced by external factors such as distractions and learned behaviors. An alternative approach, known as “pinned eating,” proposes structuring meals around fixed times and contexts.

In this episode Prof. Jane Ogden, Professor of Health Psychology at the University of Surrey, discusses these concepts and some of the research her group has carried out.

Guest Information Professor Jane Ogden is a distinguished health psychologist at the University of Surrey, with over three decades of experience in researching eating behavior, weight management, and women’s health. She earned her PhD from the Institute of Psychiatry in London in 1990 and has since contributed extensively to the field through her research and publications. Throughout her career, Professor Ogden has authored several influential books, including “Health Psychology: A Textbook,” now in its seventh edition, and “Thinking Critically about Research.” Her work is widely recognized, leading to her receiving an honorary Doctor of Science from the University of Buckingham in 2022. Timestamps

• [02:01] Interview start
• [02:41] Understanding eating behaviors and influences
• [10:33] Integrating psychology into nutrition practice
• [13:58] Pinned Eating
• [16:46] Critique of Intuitive Eating
• [21:30] Eating behaviors and hunger as a perception
• [26:34] Taste preferences and acquisition in children
• [29:10] Cultural and contextual meanings of food
• [33:25] Disgust and food presentation
• [35:29] Health communication and obesity
• [44:28] Future research in health psychology
• [47:23] Key ideas segment (Premium-only)

Links:

• Subscribe to Sigma Nutrition Premium
• Join the Sigma email newsletter for free
• Go to Sigma Nutrition website
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Study: Ogden et al., 2020 – The impact of intuitive eating v. pinned eating on behavioural markers: a preliminary investigation

Sleep is one of the most critical yet often overlooked components of health, performance, and overall well-being. Poor sleep quality or insufficient sleep can disrupt circadian rhythms, impair glucose metabolism, and alter hunger signals, leading to increased food intake, reduced insulin sensitivity, and other undesirable outcomes.

In this episode, we bring together expert discussions from some of the leading researchers in sleep science, to explore what defines high-quality sleep, the mechanisms behind sleep regulation, and the factors that influence sleep-wake cycles, from light exposure to psychological stress.

Timestamps

Note: Full episode only available on Sigma Nutrition Premium.

• [02:14] The importance of sleep duration and timing
• [05:32] Exploring sleep intensity and architecture
• [07:50] Defining good quality sleep
• [12:46] The two process model of sleep regulation
• [19:06] What is sleep?
• [24:47] Socioeconomic factors and sleep
• [34:30] The impact of blue light on sleep
• [47:10] Wake drive and sleep pressure
• [52:44] Stress, anxiety, and sleep
• [58:27] Common sleep disorders
• [01:06:26] Sleep and eating behavior

Related Resources

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Episodes referenced:
  • 38: Dan Pardi, PhD
  • 316: Michael Grandner, PhD
  • 209: Amy Bender, PhD
  • 433: Greg Potter, PhD
  • 328: Meeta Singh, MD
  • 536: Ian Dunican, PhD
  • 61: Kirk Parsley, MD

There is research suggesting that industrialization has significantly altered the composition of our gut microbiota, with certain microbial species now absent in many industrialized populations.

Given the known associations between gut microbiome diversity and health, researchers have begun investigating whether restoring lost microbial species and adopting dietary patterns similar to those of non-industrialized populations could lead to measurable health benefits.

In a newly-published study, the investigators aimed to explore whether L. reuteri could be successfully reintroduced into the microbiome through the “Restore Diet” and whether such a shift would result in improvements in key cardiometabolic and inflammatory markers.

One of the authors, Dr. Anissa Armet, is on the podcast to discuss this area and both the potential and limitations of microbiome restoration efforts.

Timestamps

• [03:48] Interview start
• [08:45] Understanding gut microbiome restoration
• [11:44] Challenges in microbiome research
• [21:03] Study design and objectives
• [43:23] Key findings and results
• [47:46] Future research directions
• [01:04:04] Key ideas segment (premium-only)

Links

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Free Book: The NiMe Diet: Scientific Principles and Recipes
• Paper: Cardiometabolic benefits of a non-industrialized-type diet are linked to gut microbiome modulation
• Dr. Armet’s free, open-access High Protein Cookbook for Muscle Health During Cancer Treatment

Every five years, the U.S. Dietary Guidelines are updated based on the latest scientific evidence to help shape national nutrition recommendations. A panel of experts was assembled to review the existing research, evaluate new findings, and provide recommendations that will inform the next edition of the guidelines.

One of the committee members involved in this process is Professor Christopher Gardner, a leading nutrition scientist at Stanford University, who joins us to share key insights from the committee’s work.

In this discussion, Professor Gardner provides an inside look into how the committee evaluated dietary patterns, the role of plant-based proteins, and the ongoing debate surrounding ultra-processed foods. He explains the rigorous process of reviewing scientific literature, the challenges in translating research into policy, and the critical role of health equity in shaping the recommendations.

By exploring these themes, this episode aims to provide clarity on the scientific foundation behind the upcoming dietary guidelines. Whether you’re a nutrition professional, researcher, or someone interested in how dietary recommendations are formed, this conversation sheds light on the key discussions shaping the future of nutrition policy.

Timestamps

• [03:38] Interview begins
• [07:18] The rigorous process behind formulating dietary guidelines
• [12:10] Key questions addressed and major findings from the report
• [25:41] Identifying nutrients of concern and refining dietary patterns
• [33:39] The importance of health equity in dietary recommendations
• [36:04] Reassessing dairy’s role in different population groups
• [41:05] Shifting the focus towards plant-based protein sources
• [47:52] The debate on ultra-processed foods and public health implications
• [58:24] Key Ideas segment (Premium-only)

Related Resources

• Enroll in the next cohort of our Applied Nutrition Literacy course
• Subscribe to Sigma Nutrition Premium
• Join the Sigma email newsletter for free
• Scientific Report of the 2025 Dietary Guidelines Advisory Committee
• Previous episode with Prof. Gardner: Episode 223

Understanding the complexities of diet-disease relationships requires a nuanced approach to nutritional science. Unlike other scientific disciplines, nutrition research often grapples with the inherent challenges of studying dietary patterns and nutrient intakes in free-living populations over long periods.

The cumulative effects of dietary exposures, combined with the necessity to control for confounding factors such as total energy intake and population-specific dietary habits, highlight the need for rigorous study designs and careful interpretation of findings.

Despite their utility, these methods are often misunderstood or misrepresented in public discourse. Addressing these misunderstandings requires a clear communication of key principles underpinning nutritional science, including the role of cumulative exposure, the importance of contextualizing absolute and relative risks, and the necessity of evaluating the long-term effects of dietary patterns.

This episode aims to provide a comprehensive overview of these essential ideas, equipping readers with the tools to critically appraise the evidence and engage meaningfully with the ongoing conversation around nutrition research.

Timestamps

• [03:26] Understanding nutrition science: core concepts
• [06:01] Standards of proof in nutrition research
• [19:39] Unique challenges in nutrition research
• [26:30] High vs. low exposure in nutrition studies
• [34:34] Challenges in nutrition randomized control trials
• [39:29] Understanding null by design in nutrition trials
• [41:58] The importance of temporal relationships in diet and disease
• [43:55] Relative risk vs. absolute risk
• [57:16] The role of substitution and adjustment in nutrition studies

Related Resources

• Enroll in the next cohort of our Applied Nutrition Literacy course
• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Episodes referenced:
  • 531: Correlation, Causation & Cliché
  • 478: Exposures in Nutrition – Why They’re Crucial to Understand
  • 511: Null By Design – When “No Effect” Doesn’t Mean No Effect
  • 378: Nutritional Epidemiology
  • 472: Compared To What? – Understanding Food Substitution Analysis & Adjustment Models

This episode focuses on the intersection of nutrition, lifestyle, and women’s health, with a particular emphasis on managing complex conditions such as PCOS, endometriosis, and premenstrual dysphoric disorder (PMDD).

Registered dietitian Marjorie Nolan Cohn shares insights from over two decades of clinical practice, highlighting the importance of addressing foundational health behaviors—such as adequate sleep, hydration, and nutrient-dense dietary patterns—before introducing targeted interventions like supplementation.

Marjorie explores the nuanced relationship between body weight, metabolic health, and fertility, while addressing misconceptions around weight loss as a primary health goal. The episode examines the role of long-term, individualized care in improving symptoms and outcomes for women experiencing significant menstrual-related challenges.

Practical considerations for practitioners, including strategies to build trust, identify key barriers, and provide holistic support, are outlined alongside the importance of interdisciplinary collaboration to improve care quality.

Marjorie Nolan Cohn is a registered dietitian with a Masters Degree in Food and Nutrition Science from the Indiana University of Pennsylvania. She is the Clinical Director of Berry Street, a company providing virtual in-network nutritional counseling to people across the US.

Timestamps

• [04:32] Beginning of the interview
• [08:39] The role of nutrition in fertility
• [13:40] Understanding PCOS and endometriosis
• [16:28] Barriers to accurate women’s health diagnoses
• [19:03] Exploring diet and lifestyle strategies
• [23:28] Addressing challenges in women’s health and nutrition
• [39:01] Closing remarks and final takeaways

Related Resources

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Guest website: Berry Street

Over the past couple of decades, renowned researcher Dr. Marie-Pierre St-Onge has uncovered fascinating links between how we sleep and what we eat, revealing how these two lifestyle factors influence energy balance, cardiovascular health, and metabolic function.

In this episode we’ll explore Dr. St-Onge’s findings on sleep regularity and its association with reduced mortality risk, providing actionable insights for optimizing your lifestyle. With a focus on combining rigorous methodologies and controlled dietary interventions, her research sheds light on the complex mechanisms connecting sleep, diet, and metabolic health.

Timestamps:

• [03:39] Dr. St-onge's academic journey and evolution of her research interests
• [07:03] Overcoming methodological challenges in sleep and nutrition research
• [10:20] The importance of sleep regularity for health
• [15:44] Exploring the bidirectional connection between diet and sleep
• [23:40] Unpacking the mechanisms linking diet to sleep quality
• [37:33] Practical recommendations for optimizing sleep and diet

Links:

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Article: How Sleep & Nutrition Interact – Alan Flanagan, PhD
• Go to episode page

Multivitamin and multimineral supplements have long been a topic of both scientific inquiry and public debate. While they are often marketed as convenient solutions for achieving nutritional adequacy, their true value remains contentious.

Are these supplements essential insurance policies against nutrient deficiencies, or are they merely expensive placebos?

Importantly, how should we weigh their potential benefits against the lack of robust evidence for long-term health outcomes such as reduced mortality or chronic disease risk? These questions demand a nuanced exploration, grounded in the context of specific populations and individual needs.

Ultimately, the role of multivitamin supplements cannot be assessed in isolation but must be viewed through the lens of context and specificity. How do we balance the biological plausibility of benefits against the variability of individual diets, the presence of fortification policies, and the challenges of achieving dietary adequacy in certain life stages?

These considerations invite a more thoughtful and less binary discussion about whether, when, and for whom multivitamins are a worthwhile addition to the diet.

Timestamps

• [00:22] The debate on multivitamins: worthless or beneficial?
• [00:53] Rationale behind multivitamin use
• [04:04] Modern nutritional adequacy and multivitamins
• [07:10] Evidence supporting multivitamin use
• [23:39] Long-term health outcomes and multivitamins
• [41:43] Cognitive outcomes
• [50:18] Pregnancy and multivitamin use

Related Resources

• Join the Sigma email newsletter for free
• Subscribe to Sigma Nutrition Premium
• Enroll in the next cohort of our Applied Nutrition Literacy course
• Shaun Ward Article: Multivitamin Madness: There’s More to Life than Death
• Studies mentioned:
  • MacPherson et al., 2013 meta-analysis of randomized controlled trials
  • Jenkins et al., 2021 meta-analysis
  • COSMOS trial – Vyas et al., 2024 analysis of three substudies
  • Loftfield et al., 2024 – Multivitamin Use and Mortality in 3 Cohorts
  • Blumberg et al., 2017 nutritional adequacy paper