I think that is true of practically everyone (not just SAD sufferers) but as with most things that happen with 'winter blues' it is quite likely that this is exagerrated for SAD people...
I find I crave sugar when i am tired. So if I eat something that I am intolerant to, or am tired either to a hard day or SAD or illnes for example I eat lots of sugar to stay awake. So even if Im full up after a huge meal - I have to have a pudding!!
I have to be aware that the sugar rush takes a number of minutes to reach me and in the meantime I could get through a few puddings etc - whilst trying to stay awake.
However, if I can work through this awful craving for a few days and not have any sugar, I can go make it go away and I start to feel better. However, Its awfully easy to slip back to my old ways. A bit like an addition!!!!!!