What can 21 days of continuous glucose and ketone data, recorded during a 1,000-mile cycling journey, reveal about managing type 1 diabetes on a ketogenic diet?

Dr. Ian Lake is a UK-based primary care physician who has lived with type 1 diabetes for more than 30 years. After two decades of conventional high-carbohydrate management, he adopted a very low-carbohydrate, ketogenic approach and began examining insulin not simply as a glucose-lowering medication, but as a metabolic hormone whose requirements are influenced by nutrition, exercise, sleep, circadian rhythm, hydration, and stress. His new book, Shifting Gears, documents the ride and the lessons he took from it.

Dr. Lake treated the journey as a 21-day personal experiment, wearing continuous glucose and ketone monitors while consuming roughly 20 grams of carbohydrate per day. In this conversation with Dr. Dominic D’Agostino, he shares what his data showed: an average ketone level near 1.2 mmol/L, daily insulin requirements declining from the mid-20s of units to around 16, and an episode in which glucose and ketones rose together after he had taken too little insulin.

Dr. Lake describes how, in his case, one unit of insulin brought his ketones from approximately 3.0 to 0.9 mmol/L within about 20 minutes. He and Dr. D’Agostino use the experience to explore the distinction between nutritional ketosis and diabetic ketoacidosis, the essential role of adequate insulin, and why ketone readings must always be interpreted alongside glucose levels and clinical context.

They also discuss insulin sensitivity during prolonged exercise, the practical challenges of adjusting insulin during endurance activity, and research suggesting that fat-adapted athletes may sustain high rates of fat oxidation at relatively high exercise intensities.

Questions Answered in This Episode

• What did 21 days of continuous glucose and ketone monitoring reveal during a ketogenic, 1,000-mile cycling journey?
• How did prolonged endurance exercise affect Dr. Lake’s daily insulin requirements?
• How is nutritional ketosis different from diabetic ketoacidosis, and what role does insufficient insulin play in DKA risk?
• What did Dr. Lake observe when his glucose and ketones began rising at the same time?
• How might fat adaptation influence fuel use and endurance performance?
• What are the practical limitations of continuous glucose and ketone monitoring for real-time insulin decisions?

This conversation offers a rare look at 21 consecutive days of glucose, ketone, insulin, nutrition, and exercise data, while also emphasizing that Dr. Lake’s experience is an individual case, not a substitute for personalized medical supervision.

More Links:

• Shifting Gears, Dr. Lake’s book, on Amazon
• Type1Keto, Dr. Lake’s site featuring the book and the Zero Five 100 project

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