We don't feel hungry during summer because our body don't need to maintain our body temperature, And during the winter days you know very well that the weather become cold and our body try to maintain our body temperature and it uses much energy than summer , so thats why we feel much hungry during winter days In summer your body does have to burn to keep warm as in the winter time burn more calories that is in the winter time if you're outside in a cold climate your body Burns a great deal of calories to stay warm