I think this was the reasoning behind the cabbage soup diet. It was supposed to burn more calories to consume/digest the soup. I tried it once, but it was disgusting. Thinking about it, the superspeed soup is probably the SW variation...
I remember the cabbage food diet... yuck!!
I lost a lot of weight in next to no time, but as soon as I ate normal, healthy meals it all came back. Same with most fad diets I guess!
I suppose it would depend how much of it you ate compared to other things. I think what Snopes is actually saying is that the calories in the celery aren't accessible i:e we can't break down the celullose (the walls of plant cells) so we have more fibre than anything else. If you look at the status of the article it actually says it's true.