Almost all of it gets used — fruit is one of the easiest things your body digests.
Here's the path your watermelon, peaches, and cherries take:
**Mouth and stomach (0–45 min).** Barely any work happens here. Fruit has no fat and almost no protein, so it doesn't linger in the stomach the way a steak would. It gets churned into a slurry and pushed on quickly.
**Small intestine (1–3 hrs).** This is where the real absorption happens. The sugars — mostly fructose, glucose, and sucrose — get split and pulled into your bloodstream. Glucose goes straight into circulation for immediate energy or gets stored as glycogen in your liver and muscles. Fructose takes a detour: it goes almost entirely to the liver, which converts it into glucose or glycogen. The water goes in here too, and your watermelon was roughly 90% water, so that alone was about 270ml of hydration.
**Large intestine (12–48 hrs).** The fiber never gets digested by you at all — you don't have the enzymes. Instead your gut bacteria ferment the soluble fiber (pectin, lots of it in peaches and cherries) and produce short-chain fatty acids, which actually feed the cells lining your colon. The insoluble fiber just adds bulk and moves things along.
Rough totals for what you ate: something like 45–50g of sugar, 7–8g of fiber, and around 200 calories — plus lycopene from the watermelon, beta-carotene from the peaches, and anthocyanins from the cherries.
One practical note: peaches and cherries both contain sorbitol, which your small intestine absorbs poorly. In the quantities you had, some people get gas or a loose stool a few hours later. Completely harmless, just the sorbitol pulling water into the gut.