I would blame it on the clothes, saying they must be shrinking in the cold winter air. Then present it as a challenge to keep up with the shrinking size of the clothes by going on daily walks/runs, bike rides together so it doesn't cost a fortune to buy all new non shrinking clothes.

And on a side note, when asked "do these jeans make my butt look big", I like to reply "no, your butt does that all on its own". Good Times always follow

M - 9 1/2 years
5/5/16 - Bomb drop - 3 week EA
10/31/16 - We sold house
01/10/18 - D Finalized