According to Su Wen classics, the 7th December marks the beginning of the Second Month of Winter, the month of the shortest days of the year. This month marks the "dark" side of the year, hence in many traditions we celebrate light festivals, keeping the light going.
As in nature so for us it is the time for exploring our own dark sides, the most inner parts of us that we rarely look into. The "indwelling power" of Water element (element of Winter) is helping us to dwell into our depths to discover or re-discover our true power, strength and identity. Here the light is needed to explore and face the darkest parts of ourselves. In antiquity, it was actually the Water that was celebrated and revered during this time. It was understood that in Nature it was Water that transported light into the dark depths of the Earth as it was the rain that transported the light of the Sun through the Winter clouds.
Therefore, it was time to give reverence to all aspects of Water, which the ancients listed as: gathering, flowing, outpouring, present, diffusing, compressing and hidden. These are both active and static qualities. It is most appropriate to dwell on these qualities in ourselves during December month, both for psychological and physical wellbeing. And as always, the key is in balancing off these extreme qualities. Living in the extreme part of the year we are more prone to extremes ourselves, so there is a word of precaution in the ancient texts.
To give some examples. We organise friends and/or family gatherings in order to connect with our identity but if we rely too much on that we may loose our own personal identity. We may want to take up running as an activity to boost our strength and stamina but we need to balance it with meditation to practice being present. We make and give presents to outpour our generosity but equally we need to save (compress) our forces and resources to arrive to the end of the Winter. Some days we may just feel like we want to hide from the world and literally go into hibernation whilst other days we may need to diffuse some of our essence to mark our presence in the world. So, just as an erratic nature of Water, so are we erratic during its season.
The prevalence of our activity during this month should be, however, of Yin quality (slow and static). Since we will not receive any external energy, as there is nearly none Yang in the Nature, and we may expose ourselves to consume much of our own reserves.
Diet wise, it is advisable to eat root vegetables and anything that has a compressed amount of nutrients (superfoods, seeds) and aquatic foods and vegetables. For those who eat meat you may notice more requirement for meat and fatty foods in Winter months as they are warming and nutritious. In order to compensate for the cold and humid-cold weather, we need to consume hot meals, soups, stir-fried or oven baked foods. We need to choose warming foods and spices like ginger, garlic, leeks, pepper, coriander, nuts, all pumpkins, to name a few. But again a word of precaution, we often go into nutritious extremes when Christmas time comes ;-)