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

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 reporter Feng Xiaohong (Medical and Health Group)

Editor/Liu Zhao New Media Editor/Chen Xuanzhi

Interview experts:

Yu Kang (Director of the Department of Clinical Nutrition, Peking Union Medical College Hospital, Chief Physician, Professor)

gossip

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.

the 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 the temperature of the skin, 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. Recently, some related rumors have appeared on the Internet: "Low temperatures slow down fat metabolism, which in turn causes fat to accumulate. The less you wear, the easier it is to gain weight."

This rumor has become a consensus among many people, and "common sense" such as "people will get fatter in winter" and "fat has a certain protective effect on the human body" seem to support this consensus. There are even rumors that fat is very "smart" and will go wherever it is cold, and will actively protect the frozen parts in winter, so the less you wear, the easier it is to gain weight, and the more exposed parts are more likely to gain weight...

These views have surprised beauty lovers who "care more about style than temperature". Does low temperature really slow down fat metabolism and accelerate fat accumulation? In fact, as long as we understand 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".

There are two main types of fat in the human body. In addition to the white fat that is commonly known to the public, there is also a very small amount 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 "conspicuous". 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 the obesity that people usually do not want to see.

Brown fat exists quietly in the human body, in small amounts and without any change in color. It is only distributed in the neck and collarbone in adults. It is responsible for consuming energy, converting fat into heat, and decomposing 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 their chests, buttocks, etc., and the distribution of fat can change with the temperature, ultimately achieving the goal of breast and buttock enlargement without the need for laborious fitness and surgery... This idea is obviously impossible to achieve. Yu Kang, director of the Clinical Nutrition Department, chief physician, and professor at Peking Union Medical College Hospital, told the Beijing Science and Technology Daily I Science Plus client reporter 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 a healthy person's body will maintain a dynamic balance. Therefore, low temperatures make it difficult for fat to flow and further accumulate. Fat is actually not so "smart", but rather very passive.

Low temperatures may not necessarily slow down fat metabolism

At the same time, fat metabolism generally does not slow down in low temperature environments, but may even 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. When the energy supply from sugar decomposition cannot meet the demand, fat will get involved.

Studies have found that human 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 thermogenesis and non-shivering thermogenesis to increase heat production in order 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. Its characteristic is that it produces a lot of heat. When shivering occurs, the metabolic rate can increase by 4 to 5 times.

Non-shivering thermogenesis is also called metabolic thermogenesis. It increases heat production through tissue metabolism, and the strongest effect is in the adipose 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 does not reduce fat metabolism and may even accelerate fat burning, does it mean that you can lose weight by wearing less in winter?

Actually, it is not true! 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 you wear less in winter, the anti-famine mechanism in the body will start and quickly find out: "It's too cold, I should increase the thickness of subcutaneous fat to resist freezing." This mechanism will secretly lower the basal metabolism a little, 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".

Being hungry and cold may help you lose weight, but it may affect your 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 disease. 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 other than brain tissue to make up for the calorie difference, which produces the "fat burning" effect.

Studies have found that the basic energy consumed by an adult Asian who does not move all 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 lifestyle and other factors, our daily calorie intake and consumption remain balanced, but are always 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 there is no reasonable exercise or other energy consumption, 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.

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