Your body loses one to two pounds of water every night just from breathing and sweating in your sleep. By morning, you're already mildly dehydrated. Any water on an empty stomach feels like relief.
Hot water on an empty stomach absorbs fast because nothing else is competing for it. Within fifteen to thirty minutes, most of it has already moved through your stomach and into the small intestine, where the actual hydration happens.
The popular reasons hot water feels so good are mostly wrong, though. Your liver and kidneys do all the detoxing in your body, and they couldn't care less what temperature your water is. And the "hot water boosts metabolism" claim is actually backwards.
A 2003 study at a Berlin hospital had healthy people drink half a liter of water and measured their calorie burn afterwards. It jumped 30% and stayed elevated for about an hour. Almost half of that calorie burn came from the body warming the water up to body temperature. If the water is already hot when it goes in, your body skips that work. You actually get a smaller calorie burn from hot water than cold. Across the day, two liters of water adds about 95 calories of extra burn either way. About a banana's worth.
What hot water does well is wake up your gut. There's a reflex in your body where, whenever your stomach stretches with food or liquid, your colon starts moving things along. This reflex is strongest in the morning. Researchers in 2019 compared three temperatures of water (ice cold, body temperature, and hot) and found the warmer two caused stronger stomach contractions than the cold one. So hot water on an empty stomach lands at exactly the time and temperature your gut responds best to. This is why people who drink it often head to the bathroom soon after.
There's also the warmth itself. A warm liquid in your throat and stomach causes the small blood vessels there to relax and widen, kind of like stepping into a hot shower on a cold day. The bloated, sluggish morning sensation starts lifting because of this relaxation effect.
So when she says "y'all weren't lying," what she's feeling is rehydration, a triggered bathroom reflex, and a warm internal hug to the gut, all hitting in the same minute. The warmth just turns up the volume on a response your gut would have anyway.
Y'all, I drank hot water on an empty stomach this morning.
Y'all weren't lying 😭