Understanding Fasting: Definitions and Dietary Approaches

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In this “Ask Me Anything” (AMA) episode, Peter revisits the topic of fasting, sharing how his thinking has evolved over time. The episode explores fasting-related terminology and common types of fasting, as well as the various reasons individuals might choose to fast. Peter explores potential benefits including improvements in body composition, metabolic health, lifespan extension, cardiovascular disease, cancer prevention and treatment, neurodegenerative conditions such as Alzheimer’s and Parkinson’s, and autoimmune symptoms like arthritis. He also examines the risks and potential downsides of fasting and offers a practical framework to help assess when and how fasting may be most appropriately applied.

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We discuss:

• Why the topic of fasting is being revisited [1:45];
• The importance of being open to changing one's opinion in science and medicine as new evidence emerges [4:15];
• Defining fasting and how it fits in the framework of dietary restriction, time-restricted feeding, and calorie restriction [7:30];
• The most common types of fasting [11:45];
• Why someone might choose fasting over continuous caloric restriction [19:00];
• The biochemical effects of fasting: fuel partitioning, autophagy, and more [21:00];
• Autophagy: a cellular cleanup process stimulated by fasting and energy depletion [26:00];
• Comparing the physiological effects of a ketogenic diet to those of long-term fasting [27:45];
• How long fasting takes to induce ketosis and boost autophagy, and how autophagy is measured [29:45];
• At-home tests for ketones [33:45];
• Reducing senescent (“zombie”) cells and inflammation through autophagy [35:00];
• Examining the evidence for the long-term health benefits of fasting beyond short-term metabolic effects [37:15];
• The common health claims associated with fasting across metabolic, neurological, oncological, autoimmune, and longevity domains [40:30];
• The impact of fasting on body weight and body composition [42:00];
• Weight regain and potential metabolic consequences of fasting [44:00];
• The risk of lean mass loss with fasting and how to mitigate it [47:15];
A practical framework for using fasting as a strategy to improve body composition [52:15];
• How extended fasting compares to caloric restriction in improving insulin sensitivity in people with insulin resistance or type 2 diabetes [54:00];
Is there any evidence that fasting can extend lifespan? [55:45];
• Examining whether fasting improves cardiovascular disease risk beyond the effects of weight loss and calorie reduction [58:15];
• Exploring whether prolonged fasting can reduce cancer risk [59:45];
• The potential benefits of fasting or fasting-mimicking diets during cancer treatment: emerging evidence and practical considerations [1:02:15];
• Fasting for protection against neurodegenerative diseases: early evidence of therapeutic benefit and open questions [1:10:45];
• Various fasting methods for autoimmune diseases: potential symptom relief with cautious application [1:14:00];
• Fasting and type 1 diabetes: risks, evidence, and careful dietary alternatives [1:16:45];
• Fasting and gut disorders: potential benefits outside of flare-ups [1:18:45];
• The primary risks and downsides associated with fasting [1:19:45];
• The essential vitamins and minerals to supplement during prolonged fasting [1:21:30];
• Who should avoid fasting and why [1:22:15];
• Fasting’s role in health: where it shows promise and where it likely offers no distinct advantage over caloric restriction [1:23:45]; and
• More.

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