2024-01-30 17:00:25
Updated on January 30, 2024, 6:00 p.m
Losing weight is often at the top of the list of New Year’s resolutions (symbolic image). © picture alliance / blickwinkel/R. Rebmann/
One wish is often at the top of the list of New Year’s resolutions: lose a few pounds. Many people gain weight, especially over the winter. But why is that actually the case? Are all the cookies to blame – or is evolution too?
Most people gain weight in the winter months – various studies show this. The worse the weather, the more attractive the sofa at home appears. With the availability of cookies and hearty food increasing at the same time, it is not surprising that the scale display is rising. This is one of the reasons why losing weight is often at the top of the list of New Year’s resolutions.
Do people need “winter fat”?
From an evolutionary biology point of view, the “winter fat” is certainly beneficial for the body: the fatty tissue protects against the cold and helps to survive the winter with a scarcer food supply.
Back in the 1960s, a study by Cambridge University found that people with higher body mass indexes (BMI) actually cool down more slowly than thinner people due to their larger fat reserves.
BMI describes body weight in relation to height and is used to estimate body fat percentage. The fat layer has an insulating effect and thus reduces the body’s heat loss – a decisive survival advantage in sub-zero temperatures.
But while wild animals such as bears and marmots still rely on their winter fat as life insurance, people in affluent countries are no longer dependent on the seasons thanks to heating and a globalized food market. Nevertheless, we gain weight in winter. So is “winter fat” a biological “habit”? Maybe we can’t do anything else?
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More food, less exercise: Who is to blame for winter fat?
In fact, we seem to eat more in the colder months than in the summer. According to a study by the University of Massachusetts Medical School, American test subjects consumed 86 more calories per day in the fall than in the spring. The composition of the nutrients also changed. The fat content in the diet was higher in autumn.
In a study at the University of Reykjavik, researchers also found evidence that people prefer higher-calorie foods in winter. Just looking at pictures with wintry scenes triggered thoughts of hearty meals in the test subjects. They interpret this as an evolutionary response to an impending winter food shortage, which actually threatened human life just 250 years ago.
In addition to calorie intake, our movement behavior also changes: The study by the Massachusetts Medical School also shows that the test subjects moved the least in the winter months. This also includes activities such as walks or gardening, which are less common in winter – presumably due to the weather. Other studies also confirm this trend.
However, the influence of physical exercise on the calorie balance is smaller than is often assumed. Exercise only influences total calorie consumption by ten to 30 percent, although the upper limit can only be achieved by professional athletes.
Are we eating to combat winter depression?
But even if you actively resist this tendency to eat more and exercise less, we gain weight faster in winter than in summer. In marmots etc., physiological processes promote the accumulation of “winter fat”: the shorter days lead to hormonal changes that slow down the metabolic rate. This promotes the buildup of fat deposits.
Daylight also has an influence on physiological processes for us humans: too little light affects our mood. When daylight diminishes, the body produces more of the “sleep hormone” melatonin – at the expense of our serotonin levels. So while the “sleep hormone” increases in winter, the “happiness hormone” decreases. The result: We feel tired and less in a good mood.
A bad mood can lead to an increased appetite. The brain tries to compensate for the serotonin deficiency by increasing desire for sweet and fatty foods. Foods with a high calorie density, such as chocolate, activate our reward system in the brain, which makes us feel better.
Too little light affects our mood. © Getty Images/Sabalete
Day length influences weight
And daylight could also have an influence on our fat metabolism: in a 2014 study, scientists at Northwestern University of Chicago found a connection between light intensity and BMI.
People who got more daylight – especially in the morning – had a lower BMI and were therefore slimmer than other study participants. Although the study with 54 test subjects is quite small and therefore only of limited significance, a study by the University of Alberta was also able to demonstrate a negative effect of sunlight on body fat cells using human tissue samples.
So there is evidence that the shorter day length in winter has a direct influence on our weight. However, the days start to get shorter from June – and while wildlife actually increases in the summer months, according to a study by the Finnish University of Tampere, Germans are at their lightest at the end of September. The weight gain cannot be explained by the dwindling daylight alone.
Study shows weight gain over the holidays
The study from the Finnish University of Tampere observed the greatest weight gain over the course of the year, especially around holidays: The researchers examined the weight changes of almost 3,000 study participants from three countries: the USA, Germany and Japan.
They discovered a pattern: the study participants gained weight especially around major holidays. The 760 German test subjects weighed an average of 0.8 kilograms more after Christmas than before the holidays. Weight gain was also noted on other holidays such as Easter, but less than on Christmas.
Among the US study participants, the weight curve started to rise at the end of November – around Thanksgiving. In Japan, on the other hand, a significant increase in weight was observed during Golden Week in early May, which coincides with several national holidays.
The fact that the scales show more in January than in October is probably mainly due to the Christmas holidays – and is favored by our body’s physiological reactions to the cold season.
A short-term and such a small increase in body weight usually has no consequences for your health. For most people, holiday fat will go away as soon as they return to their normal habits. Christmas gluttony becomes a risk when the holiday kilos don’t disappear again – and the additional cushion adds up over the years.
So there’s a lot to be said for sticking to your New Year’s resolutions like losing weight and doing more exercise – at least until the scale returns to the level it was before the holidays. But we don’t have to feel bad about the “winter fat”: evolutionary biology provides the perfect excuse.
Sources used
- Anthanont et al., 2016, Hormone and Metabolic Research: “Lack of Seasonal Differences in Basal Metabolic Rate in Humans – a Cross-Sectional Study”
- Reid et al., 2014, Plos One: “Timing and Intensity of Light Correlate with Body Weight in Adults”
- Ondrusova et al., 2017, Scientific Reports: “Subcutaneous white adipocytes express a light sensitive signaling pathway mediated via a melanopsin/TRPC channel axis”
- Cannon et al., 1960, The Journal of Physiology: “The metabolic rate and heat loss of fat and thin men in heat balance in cold and warm water”
- Helander et al., 2016, New England Journal of Medicine: “Weight Gain over the Holidays in Three Countries”
- Kuzmenko et al., 2021, Human Physiology: “Seasonal Body Weight Dynamics in Healthy People: A Meta-Analysis”
- “Seasonal cues to food scarcity and calorie cravings: Winter cues elicit preferences for energy-dense foods”
- Ma et al., 2005, European Journal of Clinical Nutrition: “Seasonal variation in food intake, physical activity, and body weight in a predominantly overweight population”
- Chan et al., 2009, International Journal of Environmental Research and Public Health: “Assessing the Effects of Weather Conditions on Physical Activity Participation Using Objective Measures”
- Nachrichtenportal Vox.com: “The science is in: exercise won’t help you lose much weight”
- Westerterp et al., 2013, Frontiers in Physiology:”Physical activity and physical activity induced energy expenditure in humans: measurement, determinants, and effects”
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