So this is something I just had an AHA moment about, and ran my hypothesis through the resident genius in my browser.
After ONE night out (a party, or dinner where I have maybe 2-3 beers) where I exceed my baseline by maybe 500 calories, I find that I put on 3-4 pounds. No surprise there really -- water weight can add up quick. But it takes 4-5 DAYS for things to return to normal -- and that gets kind of demoralizing. But...

What Happens When You “Refeed” After a Deficit -- Glycogen Replenishment
After sustained calorie deficit (especially low carb or high activity), your muscle and liver glycogen stores are partially depleted. A meal rich in carbs and alcohol triggers rapid glycogen resynthesis. And for every 1 gram of glycogen, your body stores ~3–4 grams of water with it.
Let’s say you replenish 400g of glycogen (moderate estimate) → that's ~1.6 kg (3.5 lbs) of combined glycogen and water. This explains the overnight jump.
If you return to a modest deficit, it may take several days to fully re-deplete that glycogen. Once that happens, your body sheds the water over a day or two.
Beer = carbs + alcohol → spikes insulin, suppresses fat oxidation, and encourages glycogen refill. Alcohol also causes fluid retention initially, then mild dehydration (hormonal rebound can confuse things). Salty foods often eaten alongside amplify water retention further.
Summary
- Glycogen refill +300–600g glycogen + 1.2–2.4kg water
- Sodium from party food Additional water retention
- Alcohol Mixed effects: insulin, fluid retention, delayed fat burning
- Re-deficit after Gradual glycogen use → water release
- Releasing a lot of fluid on day 4–5 Hallmark of glycogen + water loss
Bottom Line: Your body is very good at restoring glycogen when re-fed, and the scale jump is mostly water + glycogen, not fat. If you return to your deficit, the weight loss resumes as expected — shedding excess water after 4–5 days, just as you described.
Maybe this will help someone else keep the faith after a "bad" day. Seeing the scale go up and get stuck for almost a week after a single night out is such a buzzkill. But it's temporary -- get back on the horse and you'll shed it again, even if it takes a few days. At most you gained 3-4 'real'
ounces.