Answer:
When you are homeless you often don't eat as many meals and get as many nutrients as you need. The human body will begin to cling to nutrients when starved. If a homeless person gets into a financally stable place where they eat every meal it will take their body a while to adjust. They will begin to gain several pounds while their body adjusts back to recieving daily nutrients instead of starving itself.
I hope this helps a bit :) Have a nice day!