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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• 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?

Fructose has often been labeled a uniquely damaging nutrient, blamed for obesity, diabetes, and other metabolic diseases. But does fructose truly have unique harmful effects or are the risks associated with it related to context and quantity?

The episode explores how fructose is metabolized in the body, why it gained a reputation for being problematic, and what the scientific evidence says about fructose in our diets. You will gain insight into why fructose was singled out in the past (e.g., its unique pathway in the liver and lack of insulin response), and how newer studies put those concerns into context.

It covers important nuances for practitioners and health-conscious individuals, especially given public confusion and fear around fructose (even in fruit).

Dr. Scott Harding, Ph.D., is an Associate Professor of Nutritional Biochemistry in the Department of Biochemistry at Memorial University of Newfoundland. His research explores the complex interactions between diet, metabolism, and chronic disease, with a particular emphasis on the metabolic effects of dietary sugars (especially fructose), the role of fats and phytosterols in lipid metabolism, and how public health policies like sugar taxation influence population health outcomes.

• [02:58] Dr. Harding’s academic background
• [08:45] Fructose metabolism in detail
• [12:51] Fructose in diet and public health
• [23:07] Current research
• [29:53] Identifying biomarkers for fructose overconsumption
• [31:12] Fructose impact on health
• [40:58] The food matrix
• [45:10] Personalized nutrition and future research directions
• [54:06] Key ideas segment (premium-only)

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• Related podcast episodes: #476, #468, #155
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Vitamin A is often one of the less-discussed micronutrients in relation to bone health, taking a back seat to nutrients like calcium and vitamin D. Yet this fat-soluble vitamin plays a fundamental role in skeletal development, remodeling, and mineral homeostasis. It influences gene expression in both osteoblasts and osteoclasts, and contributes to the regulation of bone turnover throughout the lifespan.

But what makes vitamin A particularly interesting, and controversial, is that its effects on bone appear to follow a double-edged pattern. While it’s essential for bone formation, several large epidemiological studies have suggested that chronically high intakes of preformed vitamin A may actually increase the risk of osteoporosis and fracture, especially when consumed as retinol from supplements or high-liver diets. And yet, the picture is not so clear-cut.

This raises compelling questions:

• Is the concern over vitamin A and bone health justified, or is it a case of context-dependent risk?
• Can vitamin A, when combined with adequate levels of D and K, actually support bone strength?
• And are there thresholds above or below which risk increases?

In this episode, we explore the human evidence on vitamin A and skeletal health, looking not only at fracture outcomes and bone mineral density data, but also at nutrient interactions, mechanistic plausibility, and the implications for supplement use in well-nourished populations.

Note: This is a Premium-exclusive episode, so you will only hear a preview on this public feed.

• [00:23] Vitamin A and bone health: an overview
• [02:50] Forms of vitamin A: retinol and carotenoids
• [04:16] Mechanisms of vitamin A in bone physiology
• [17:52] Nutrient interactions: vitamin A, D, and K
• [31:03] Practical takeaways and recommendations

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