Weigh yourself with a digestive tract full of food and water, then weigh yourself after fasting for a day. At 200lbs I can swing the scale 15lbs/6+kg. Fat people can probably swing some serious numbers.

Seems like a pretty unusual swing though. Gorging then fasting is certainly not typical behavior.

I can see this happening given such behavior, as well as in the "heavier" portion of the population. definitely not a common occurrence across the population though.

It's doable depending on your body size. I'm 180cm and 95 to 99 Kg depending on the day.

When I do weight loss, I can plot it daily and it's going down on average but there are large swings on most days.

I can gain or lose on the order of 15lbs in a single day when switching to/from a ketogenic diet due to water retention.