The fact that in winter we tend to be hungrier and eat more is not only due to psychological, social, cultural factors, but also to one specific brain nucleus of the thalamus called xiphoid nucleus (Xi). This nucleus is activated after a long stay in the cold because the energy expenditure in our body it becomes noticeable and needs to accumulate more by nourishing itself: in other words, we need more calories to have effective thermoregulation and for this reason we feel the need to eat more. The xiphoid nucleus works just like a “switch” that causes the body to search for food when it needs it. The experiments, carried out on guinea pigs in the laboratory and with advanced brain imaging techniques, they have made it possible to understand the specific neurons that control the reactions to the energy deficit induced by cold. However, the greater consumption of food in cold periods is also the result of a combination of biological needs, psychological adaptations and cultural influences, such as the habit of eating caloric and abundant meals during the holidays.
In winter we eat more because we expend more energy
Humans, like all mammals, have a system of thermoregulation which allows you to regulate your body temperature. In winter, due to the cold, we mammals invest a lot of energy to keep our body temperature stable and to compensate for this greater energy expenditurewe tend to eat more.
The regulation of this mechanism has been clarified by experiments on mice made by a team of biomedical researchers from the Scripps Research Institute located in La Jolla, which includes professors Li Ye and Neeraj Lal. The results of this research were then published in the journal Nature. Researchers have identified a specific area of the brain, the xiphoid nucleus (Xi) in the medial thalamus as the main protagonist of this process, in particular i XiCIEC neurons present inside it.
The experiments were conducted on mice in the laboratory exposed to a temperature of 4°C: under these conditions, the mice gradually increased their food consumption, but not immediately. Thanks to advanced techniques for mapping the function of the Nervous System, called techniques neuroimaging (or brain imaging), the Xi nucleus was observed to begin to activate during exposure to cold and its activity increases just before the mice start eating. This suggests that the Xi prepares his brain to undertake specific eating behaviors linked to energy needs.
Finally, thanks to techniques that allow us to probe neuronal circuits (optogenetic methods) and molecular engineering techniques (chemogenetics), it has been possible to manipulate the activity of the Xi nucleus and demonstrate that the stimulation of this region increases the search for food in mice, while its inhibition reduces this response.
How the mechanism that pushes us to be hungrier in winter works
The Xi nucleus plays a crucial role in the regulation of eating behavior in response to falling temperatures. Its activation is based on a series of neurological mechanisms and connections with other brain areas, it is linked to the increase in energy expenditure that the body must face in response to cold. When activated, it helps the body balance energy conservation and food seeking in cold conditions, as a kind of “switch“.
The Xi is not activated after immediate exposure to cold, but is activated in response toprolonged exposure in the cold: it has what we can call a temporal selectivity. In fact, this part of the brain is activated only after approximately 6 hours of exposure to low temperatures (approximately 4°C), when theaccumulated metabolic demand, i.e. the increase in body energy consumption requires food compensation. This phenomenon was called Cold-Induced Energy Compensation (CIEC).
Xi is activated in a highly specific manner and exclusively in relation to the energy deficit associated with thermoregulation and cold-induced eating behavior. Indeed, Not it is involved in other forms of appetitesuch as those related to hunger resulting from fasting, low blood glucose levels, or simply general hunger.
The Xi regulates and allows the transition from one behavior of energy conservation (staying still to save energy) to food-seeking behavior, thanks to the connection of the Xi itself with the Nuceo Accumbens, a brain region that plays a fundamental role in motivation and in the circuits of reward of the brain. This is a key point in understanding how the brain balances energy conservation and consumption under challenging natural conditions.
Winter and increased appetite: psychological and cultural factors
While not everyone responds to cold the same way, the reasons behind this behavior are rooted in both evolution and social dynamics. In fact, there are also factors physiological, psychological And cultural which influence why we tend to eat more in winter.
For example, cold weather also affects hunger hormones, which stimulate food cravings. On a psychological level, the effect that winter has on our psychology due to the less exposure to sunlight, factor that could lead to using food as an outlet or to relieve depressive symptoms.
Finally, it is also important to consider cultural factors such as, for example, culinary traditions of the mandatory holidays that promote the consumption of substantial and rich foods, and the preference of high calorie foodsbe it how comfort foodand to keep warm.
