My fat loss experiments with ChatGPT and water fasting
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- Lakshmipathi G, a FOSS developer, lost approximately 14kg and 4.5 inches off his waist over four months by completing sixteen weekly 40-hour water fasts, shifting from "obese" to "overweight" on the BMI scale — roughly 1kg per week.
- The fast schedule ran Friday 5pm to Sunday 9am each week (~40 hours), with protein-rich rather than carb-heavy meals on eating days to ease hunger around the 24-hour mark.
- ChatGPT functioned as a real-time monitor throughout each fast — answering hourly body-state questions, recommending a pinch of salt with water for sodium when headaches appeared, and prescribing fiber followed by protein-rich foods when breaking the fast.
- ChatGPT also addressed the author's kidney stone concerns, recommending 3 liters of water daily and noting that dehydration is a major cause of kidney stones.
- The author originally attempted a single 72-hour fast but broke it at 44 hours from hunger, then pivoted to a rolling weekly 36–40 hour fast based on a comment claiming that approach yields better results.
- The author says he also tried Claude during the experiment but relied on ChatGPT as his primary tool, repeatedly disclaiming that the protocol worked for him and may not work for others.
Why it matters: For users experimenting with extended fasts, the post illustrates how a general-purpose chatbot can substitute for a dedicated fasting coach — answering hourly body-state questions, addressing electrolyte and hydration issues, and guiding fast-breaking meals. The author's documented 1kg-per-week loss over four months of 40-hour fasts gives the experiment a concrete benchmark, though he repeatedly stresses this worked for him and may not generalize to readers with medical conditions.
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