Fat goes to where it's cold, so exposed areas are more likely to grow fat? See the proof

In winter, when the temperature is low, will fat metabolism slow down? The less you wear, the easier it is to gain weight? Exposed areas are more likely to grow fat? Check out these "heavyweight" questions about your body >>>

Written by Feng Xiaohong Edited by Liu Zhao Interviewed expert: Yu Kang (Director of Clinical Nutrition Department, Peking Union Medical College Hospital, Chief Physician, Professor)

[Rumor ] Low temperatures slow down fat metabolism, which in turn causes fat to accumulate. The less you wear, the easier it is to gain weight. And fat is very smart, it will go to where it’s cold, so it’s easier to grow fat in exposed areas.

【Truth】The metabolism of fat may not slow down in a low temperature environment, but may speed up. In a cold state, in order to maintain skin temperature, the body will speed up metabolism to ensure energy supply. The largest energy supply in the human body is sugar, and when the energy supply from sugar decomposition cannot meet the demand, fat will get involved. The energy metabolism of human beings is most stable in an environment of 20℃ to 30℃. When the ambient temperature is below 20℃, the metabolic rate begins to increase. When it drops below 10℃, the metabolic rate increases significantly, and fat metabolism also speeds up accordingly.

Every winter, the relationship between cold and fat becomes a hot topic. There are always some related rumors on the Internet: "Low temperature will slow down fat metabolism, which will cause fat to accumulate. The less you wear, the easier it is to gain weight." This rumor has become a consensus among many people, and "people will gain weight in winter" and "fat has a certain protective effect on the human body" and other "common sense" seem to support this consensus. There are even rumors that fat is "smart" and will go to where it is cold. In winter, it will actively protect the frozen parts, so the less you wear, the easier it is to gain weight, and the exposed parts are more likely to gain weight... These views have surprised beauty lovers who "prioritize style over temperature". Will low temperature really slow down fat metabolism and accelerate fat accumulation? In fact, as long as we clarify the relationship between fat and human heat production, we are close to the truth.

Go wherever it's cold? Fat isn't that smart

Most people may take it for granted that fat is a barrier for the human body. When the cold comes, fat gathers like an army to stand guard in the cold places of the body. But fat cannot "go to where it's cold". In the human body, there are mainly two colors of fat. In addition to the white fat that is widely known to the public, there is also a very small distribution of brown fat. The two colors of fat have different functions in the human body.

▲Brown adipose tissue (left) and white adipose tissue (right) slices. Image source: Dr Saverio Cinti (University of Ancona, Ancona, Italy). Scale bar: 40 μm

White fat is abundant and "flaunting". It is widely distributed in the subcutaneous tissue and around the internal organs of the body. It is mainly responsible for storing energy. It can store excess energy in the body in the form of fat, forming obesity that people usually don't want to see. Brown fat exists quietly in the human body, with a small amount and "no movement". It is only distributed in the neck and clavicle in adults. It is responsible for consuming energy, converting fat into heat, and can decompose white fat that causes obesity, converting the latter into carbon dioxide, water and heat, which can speed up the body's metabolism and promote the consumption of white fat. Assuming that fat really increases and decreases with temperature changes, then people who need to shape their bodies can use specific instruments to cool the chest, buttocks, etc., and the distribution of fat can change with temperature, ultimately achieving the purpose of breast and buttock augmentation, without the need for laborious fitness and surgery... This idea is obviously impossible to achieve. Yu Kang, director of the Department of Clinical Nutrition, chief physician, and professor of Peking Union Medical College Hospital, told reporters from the Beijing Science and Technology Daily client that because the distribution of human fat is relatively stable, this is the result of body heat balance-the heat production process and heat dissipation process of healthy people will maintain a dynamic balance. Therefore, low temperatures make it difficult for fat to flow and further accumulate. Fat is not so "smart" but rather very passive. Low temperatures do not necessarily slow down fat metabolism.

At the same time, fat metabolism generally does not slow down in a low temperature environment, but may accelerate. In a cold state, in order to maintain skin temperature, the body will speed up metabolism to ensure energy supply. The energy required for all life activities of the human body mainly comes from the oxidative decomposition of sugar, fat and protein in the body. Among them, sugar provides the most energy, and when the energy supply from sugar decomposition cannot meet the demand, fat will get involved. Studies have found that people's energy metabolism is most stable in an environment of 20℃ to 30℃. When the ambient temperature is below 20℃, the metabolic rate begins to increase. When the ambient temperature drops below 10℃, the metabolic rate increases significantly, and fat metabolism also speeds up accordingly. This is related to the heat production of the human body under cold stimulation. In a cold environment, people mainly rely on shivering heat production and non-shivering heat production to increase heat production to ensure body heat balance and maintain body temperature.

▲Human body temperature distribution under different ambient temperatures, A is an ambient temperature of 20°C, B is an ambient temperature of 35°C (picture from the Internet)

Shivering (also known as shivering) refers to the involuntary rhythmic contraction of skeletal muscles. It is the main way for adults to produce heat in cold conditions, and its characteristic is that the heat production is very high. When shivering occurs, the metabolic rate can increase 4 to 5 times. Non-shivering heat production is also called metabolic heat production. It increases heat production through tissue metabolism. The strongest part is the fat tissue distributed in the subscapular area, around the large blood vessels in the neck, and in the groin. This is also the main way to consume fat in low temperatures.

Getting fat or losing weight depends on the energy gap

If the cold doesn’t reduce fat metabolism, and may even speed up fat burning, does that mean that wearing less in winter will help you lose weight? Actually, not really!

Scientists have found that the human body has a natural stress response to environmental changes. Wearing less and getting cold may result in getting hungry faster and eating more each time. Because people wear less in winter, the body's anti-starvation mechanism will start and quickly find out: "It's too cold, so I should increase the thickness of my subcutaneous fat to resist freezing." This mechanism will secretly lower the basal metabolism, save a little energy every day, and turn it into subcutaneous fat. So if you want to lose weight, it's not enough to just be "cold", you have to be "hungry and cold". "Hungry and cold" may help lose weight, but it may affect our health. In winter, in order to help the human body switch to "energy-saving" mode, the vascular tension of the local skin increases, causing the body temperature of the limbs, especially the hands and feet, to drop, which may cause peripheral vascular diseases. Long-term exposure to low-temperature environments can even directly lead to frostbite and hypothermia, and increase the risk of cardiovascular and cerebrovascular diseases.

Whether we get fatter or thinner depends mainly on the energy gap. "If you eat less and consume more, there will be a negative energy balance, that is, energy deficiency, and people's obesity can be reduced; on the contrary, if you eat more and consume less, there will be a positive energy balance, and if there is an energy surplus, people will easily gain weight." Yu Kang explained. Just as when talking about weight loss, almost everyone shouts a slogan - control your mouth and move your legs. These six words reveal the fundamental reason for fat changes: thinness is because the human body "takes less and consumes more."

▲Daily energy consumption (picture from the Internet)

The three types of nutrients in the human body, sugar, fat and protein, contain chemical energy that can be used by the body and are the energy source for human activities. Fat is an important energy supply substance in the human body and the main form of energy storage.

Generally speaking, 30% to 50% of the energy consumed by the body comes from fat. If we consume more calories than we take in in a day, the body will have to break down fat outside the brain tissue to make up for the calorie difference, which results in a "fat burning" effect. Studies have found that the basic energy consumed by an adult Asian who does not move for a day to maintain breathing and organ function, that is, the basal metabolic rate, is about 1200 to 1500 kcal. There are slight differences between different individuals. Affected by daily lifestyles and other factors, our daily intake and consumption of calories remain balanced, but they are all higher than the basal metabolic rate.

▲Daily basal metabolic rate calculation method (from @叶子健身, sports nutrition textbook) We can calculate our own basal metabolic rate. Although it is only a reference value, it can be used as a reference for formulating effective diet and exercise plans. If the daily energy intake has not reached the basal metabolic rate, there will be health risks in the long run; if the daily energy intake is equal to the basal metabolic rate, with the energy consumption caused by daily activities and winter cold protection, there will be a fat-reducing effect; if the daily energy intake is much higher than the basal metabolic rate, and no reasonable exercise or other energy consumption is performed, there will inevitably be a risk of obesity and weight gain, which has little to do with how much you wear.

References:

1. Zhu Danian. Physiology (9th Edition)[M]. Beijing: People's Medical Publishing House, 2018: 208-214.

2. Xu Bifang. Weight loss methods suitable for different ages, different physiques, and different groups of people [M]. Beijing: Chinese Medicine Ancient Books Publishing House, 2016: 28-29.

3. Ma Shengxue. Imbalance: Why we can’t get rid of obesity and chronic diseases[M]. Beijing: CITIC Press, 2018.

4. Lu Huanyu, Luo Wenjing. Translational application of low temperature environment in the prevention and treatment of metabolic diseases[J]. Chinese Journal of Disease Control, 2020, 24(07): 745-747,784.

5. Shang Jing. Winter is a good time to exercise and lose fat[J]. Family Medicine, 2018, (12): 56.

6. Tong Mei, Chen Lili, Wang Bo, et al. Regulation of human body temperature and analysis of winter cold-proof clothing[J]. China Personal Protective Equipment, 2014, (1): 13-15.