There would have to be a limit. Several things come to mind.
The people you hear about are grossly fat; they aren’t “big” in the sense that their skeleton and other organs are larger than normal, they have a lot of fat on a more or less normal sized frame.
As Arnold pointed out these people already can’t walk. Past a certain point they would probably have trouble breathing; the weight of the fat over their chest would prevent it from expanding.
The square/cube law would come into effect at some point and they would overheat. Fat is also an insulator. At some point they would become very succeptable to heatstroke.
All of that tissue is living. It has to get oxygen and nutrients. Again, they would reach the point where their lungs couldn’t provide enough oxygen for their body and they couldn’t eat enough to support it.
There are others, but these are the ones that immediately come to mind. I can’t tell you what the upper limit is, but there obviously is one.
“Drink your coffee! Remember, there are people sleeping in China.”
Dennis Matheson — firstname.lastname@example.org
Hike, Dive, Ski, Climb — www.mountaindiver.com