How to help my little chinese hamster lose some weight?

I am currently feeding him Nutriphase Gold.At first,he digs around in his food(i dont give him alot) looking for the sunflower seeds.Then he goes back for everything else.Lately,he has been sleeping all night and all day(i have insomnia so i usually check on him at night) so he hasnt been running on his wheel.Eat Sleep Drink.Thats his schedule.Because of that,he has bee packing on a little bit of weight. i know he has grown ALOT since we bought him,but now he seems to walk(more like a waddle) closer to the ground.I play with him every opportunity i get when he's awake.I know that some hamsters go into a deep sleep when temperatures drop too low.It got pretty chilly monday night.Do hamsters get fatty before sleeping or something like bears do?Sorry for the stupid question.