I Tried Fasting During Austin's 110°F Week. My Body Had Opinions.
Summer solstice was not supposed to feel like the surface of Mercury. But last week in Austin, the thermometer hit 110°F three days in a row. ERCOT set an all-time demand record of 91,308 MW on July 22. My apartment AC ran nonstop. And I was sixteen hours into a fast.
I am not an idiot. I mean, maybe a little. But I wanted to know: does intermittent fasting work when it is literally dangerous outside? I had data from 312 tracked days. None of them involved heat indices of 115°F. So I ran an experiment. Three days. Same 18:6 protocol. No AC adjustments. No extra electrolytes at first. Just me, my fasting window, and the Texas sun.
Day one was fine until 1 PM. I woke up at 7, black coffee, usual routine. By noon I was at my desk designing a dashboard for a client. Then the headache started. Not a caffeine headache. A different one. Dull, behind the eyes, the kind that makes you squint at the screen. I checked my fasting tracker. Hour 17. I had done hour 17 a hundred times. But not at 110°F.
Here is the thing. When you fast, your body loses electrolytes faster than you think. Sodium, potassium, magnesium. In normal weather, you can get away with water. In a heat wave, water alone flushes out more electrolytes without replacing them. By hour 19, I felt lightheaded standing up. I broke my fast early at 2:30 PM with salted watermelon and feta. I felt better in twenty minutes. The salt was the hero, not the calories.
Day two, I got smarter. I added LMNT to my water at hour 14. I moved my eating window from 12 PM-6 PM to 10 AM-4 PM. This was annoying because my roommate wanted to get Torchy's at 7 PM. I said no. She called me boring. I called her data-illiterate. We both laughed. The earlier window meant I was eating during the relatively cooler part of the day, and I was not trying to sleep while digesting tacos in a 78-degree apartment.
The metabolic analyzer on my site says ketosis usually starts around hour 14 for me. In the heat, it hit hour 12. My guess? The body was burning through glycogen faster to regulate temperature. I do not have peer-reviewed proof. I have my glucose meter and a spreadsheet. That is enough for me to form a hypothesis.
Day three, I added a cold shower at hour 16. Game changer. Not because it was pleasant. It was brutal. But my core temperature dropped enough that the final two hours of the fast felt normal. I broke the fast at 4 PM with a massive salad, avocado, and grilled chicken. My energy was actually higher than usual. Maybe because I was not fighting the heat anymore. Maybe because I finally respected the variables.
So here is my honest takeaway. Fasting in extreme heat is not impossible. It is just not the same fast. You need electrolytes. You need an earlier eating window. You need to accept that your body is doing two hard things at once: thermoregulation and fuel switching. Demanding perfection from both is honestly kind of rude.
I logged all three days in my fasting session tracker. Consistency score for the week: 71%. Lower than my usual 85%. But I am counting it as a win because I did not pass out in a parking lot. Sometimes the bar is low. That is fine.
Sarah, Austin
