I always tell myself for winter cycling, not to beat myself up for cycling less. That my body does require more energy to keep warmer.

As long as I cycle several times per week and if possible for myself, add in 1-2hills on some of those rides, to get my heart working harder. That type of psychology works for me.

For certain, I feel "heavier" when winter cycling under colder temperatures and with more layers.

There is a great article in Impact magazine, on body's use of energy for cold weather sports but unfortunately not online.