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Metabolic Health
Take control of you health
The Book
In April 2025, Dr. Mackenzie co-authored Stress Tested: How the New Science of Stress Hormones Can Transform Your Health with journalist Peter Walker. Published by Bluebird (an imprint of Pan Macmillan), the book explores how chronic stress affects the body, including its impact on hormones, weight, type 2 diabetes, fertility, and early life development. It challenges common assumptions—such as the belief that low-carb diets and high-intensity interval training (HIIT) are universally beneficial—by highlighting how these practices can elevate cortisol levels and disrupt glucose metabolism. The authors also examine how socioeconomic stressors, like poverty, contribute to health disparities beyond just diet and exercise factors.
Dr Mackenzie
Stress Tested has been praised for its accessible and evidence-based approach to understanding stress. It emphasizes that while stress is often driven by external factors beyond individual control, gaining insight into how stress hormones function can empower people to mitigate their long-term health effects.​
If you're interested, I can help you find where to purchase the book or provide more information on its key topics.
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Synopsis
'Read this and add at least a fortnight to your life.' – Jeremy Vine
'Real, down-to-earth and urgently needed.' – Oliver Burkeman
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Why do we feel stress? And how can we change things?
Stress Tested is a pioneering collaboration between leading researcher Richard Mackenzie and journalist Peter Walker. Investigating the science of stress hormones, real-life case studies, the history of stress, societal factors and how they interact with stress, Mackenzie and Walker explain exactly how stress works, and what we can do to mitigate its long-term health impact. This is the book exploring the nuances of stress and how it affects you.
You’ll learn how stress impacts and interacts with:
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Your hormones
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Weight
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Type 2 diabetes
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Your work and socio-economic status
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Fertility and pregnancy
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Early childhood and upbringing
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Plus some strategies for coping with stress
It is packed with conversation-starting science and stories. Did you know that low-carb diets can increase cortisol levels, as can HIIT exercise, causing insulin and glucose surges? The opposite of what we have been told in recent times. Or how stress hormones can affect fertility for all genders? Mackenzie and Walker dive into society and stress, considering if the higher rate of type two diabetes in disadvantaged communities is entirely due to lack of healthy food and exercise – or is the stress of poverty itself a major factor?
One thing is clear: stress is complex and personal, with many contributing factors. In Stress Tested, the authors present the view that much (if not most) stress is caused by factors outside of your control. It’s not your fault if you’re stressed. But having the knowledge and understanding of what is happening in your body when stress occurs is a powerful step towards minimizing it.
