Science

Why do we gain weight over winter?

January is usually the month for a new start, and for most that means losing the few extra pounds they put on over the winter period. The winter months usually mean excessive eating, nights spent in front of the TV rather than facing the cold, and an extreme lack of enthusiasm for exercising. Sure the festive period and cold weather are never good for the waistline, but what is it about winter that makes us put on weight?

The heating
It may seem like a luxury to have the heating on in most student houses, but that extra heat means the body stops burning calories to keep warm. A Dutch university found that the ideal temperature is 19C. Research found that 90% of an average person’s time is spent in doors, so controlling the temperature prevents the body using energy. The cold leads to an increase in brown fat deposits. These generate 300 times more heat than other organs in the body, naturally causing you to lose weight. With the heating turned up there is less brown fat using energy from food to generate heat.

Extra heat means the body stops burning calories to keep warm.

We over eat during the holidays
It’s quite obvious that the pounds creep up over Christmas time as we eat several Christmas dinners as well as copious amounts of chocolate and alcohol. Studies vary in their opinions of how much weight people, on average, put on over Christmas, with weight gain varying from 0.5kg to 2.3kg. Although results on how much people gain in the winter differ, it has become apparent that many do not lose it after Christmas. A study by the National Institute of Child Health and Human Development discovered that adults weigh more in February than they did September/October of the previous year. Their weight did not significantly change by September the next year, meaning that people gain more weight year on year.

As people are less happy during the winter months, high energy, high calories foods are used as comfort foods, which contain high sugar and fat. The high sugar content in these foods leads to a rapid, short-lived increase in blood sugar. This is followed by a sudden drop, leading to a vicious cycle of you craving more. As we exercise less during the winter and require less energy, all the surplus calories are stored as fat. Fat from excess calories is stored as white adipose (fat) tissue. The fat that keeps you warm is brown tissue which is what babies have. White fat stores energy, whilst brown fat breaks down calories for heat.

Studies suggest that people with low levels of vitamin D store more fat as it reduces fat breakdown into energy.

We feel more down during the winter months
People may eat more when it’s cold, and want to hide from the cold due to a winter depression called Seasonal Affective Disorder (SAD). The symptoms of SAD include comfort eating, being less active and sleeping more. The symptoms begin in early winter as the days get shorter and there is less light. Sunlight affects chemicals and hormones in the brain. Although it is not known how sunlight directly affects the brain is it believed to stimulate the hypothalamus which controls mood and appetite. It is thought to affect the hormones melatonin (which makes you feel sleepy) and serotonin (which controls your mood). Sleep may be affected as the lack of sunlight affects the body’s circadian rhythm. Your vitamin D levels drop during the winter as people are exposed to less sun. Studies suggest that people with low levels of vitamin D store more fat as it reduces fat breakdown into energy.

Jessica Hewitt-Dean

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