I used to think this, but I don't now. I actually lost 9 pounds in 3-4 days, when I had norovirus last year. Unfortunately, within 3 weeks, I'd gained it all back, (coz it was mostly water!) So it's a little bit pointless really, just losing 8 to 10 pounds for less than a month before it all goes back on.
All that suffering, in absolute agony... vomiting and diarrhoea for two or three days, just to lose just over half a stone, that you gain again within a few weeks? What's the point?