Environmental factors and obesity risk: the effects of dietary habits, lifestyle, and endocrine disruptors

2. Environmental factors Environmental factors are the main cause of increased obesity prevalence, mainly due to increased calorie intake and reduced physical activity. In addition to increased calorie intake, dietary structure also has a certain impact. Fat is more likely to cause fat accumulation than sugar. A large intake of non-starch polysaccharides/fiber is considered a factor in preventing obesity, while a large consumption of fast food, sugary drinks and fruit juice is considered a risk factor for obesity. Maternal malnutrition, protein deficiency or low birth weight during fetal development can lead to obesity in adulthood. In addition, a variety of endocrine disruptors have a promoting effect on obesity, including bisphenol A (BPA), phthalic acid, dioxin analogs and polychlorinated biphenyls, etc., whose mechanism is related to estrogen-like effects. (1) Dietary habits: With social development, people's living standards have improved and the pace of life has accelerated, and dietary habits have changed. High-energy diets and bad dietary habits are a major factor causing obesity. The continuous intake of high-carbohydrate foods provides the body with excess energy. The excess energy is converted into fat and reduces the breakdown of fat already accumulated in the body, leading to more fat accumulation in the body. High glycemic index (GI) foods such as potatoes and vermicelli can cause a rapid rise in blood sugar, making it difficult to metabolize and increasing the likelihood of it being converted into fat. It has been reported that consuming large amounts of low GI foods has a significant weight-loss effect. Poor eating habits, such as an insufficient breakfast or a poor lunch, will lead to overeating at dinner. At night, activity levels are lower, and the parasympathetic nervous system controlling gastrointestinal activity is more active than during the day, leading to increased peristalsis, secretion, absorption, and anabolism, as well as increased insulin secretion. Even with the same or smaller food intake compared to daytime, better digestion and absorption can still cause obesity. Vegetables and fruits provide the body with comprehensive nutrients, such as dietary fiber and various minerals, which help regulate metabolism and reduce the intake of high-energy foods, thus reducing the conversion of excess energy into fat. They also help regulate the balance of trace elements in the body, promoting efficient bodily function and keeping the body in an active state. Studies have shown that increasing the intake of vegetables and fruits in the family diet can reduce the risk of obesity among family members. The key to obesity is the issue of fat, as fat is the main form of energy storage in the body. Stored fat is rapidly broken down when the body needs it. Once the balance between fat storage and breakdown becomes unbalanced, with storage exceeding breakdown, fat accumulation leads to obesity. Excessive fat storage often occurs before puberty, while insufficient breakdown is the main cause of obesity in adulthood. Failure to properly manage key periods that contribute to obesity can trigger it. ① During infancy, the body's cells are in a phase of active division and proliferation. Improper diet leading to excess energy will cause all tissues, including fat cells, to enlarge, laying the groundwork for future obesity. ② Puberty is a crucial period for the gradual development and maturation of various organs and tissues. The basal metabolic rate increases, and appetite is strong. A diet high in fat and sugar, coupled with little physical exercise, often results in excess energy, ultimately leading to obesity. ③ After middle age, various physiological functions decline, physical activity decreases, and endocrine factors contribute to fat accumulation. ④ Pregnancy and childbirth are special physiological periods in a woman's life. After childbirth, influenced by traditional beliefs, women often receive far more nutrition than their bodies need, and with little physical activity, excess energy is generated. From the perspective of the mother's physique, the abdomen that expanded during pregnancy is particularly loose at this time. The cells that proliferated and enlarged during pregnancy return to a normal physiological state, and the loose abdominal wall is easily filled by fat cells. ⑤ The cold winter is the time of year when it is easiest to gain weight. In winter, the climate is cold, activities are reduced, the basal metabolic rate decreases, and energy consumption is very low. However, people's diet is much better than usual in winter, and food is abundant. Therefore, it is easier to gain weight in the cold winter. Vitamin B₆, vitamin B₁2 and niacin play an important role in the decomposition and metabolism of fat. The content of zinc is negatively correlated with triglycerides in fat. The conversion of energy substances in the body is inseparable from calcium, iron, vitamin A, etc. Therefore, when the body lacks these elements, the body's energy metabolism is affected, and excess energy is converted into fat and accumulates in the body, causing obesity. (2) Lifestyle habits: The sedentary lifestyle is considered a risk factor for obesity. Sitting for a long time will reduce the individual's activity level, thereby reducing the consumption of energy in the body and indirectly increasing the intake of energy in the body. Excess energy is converted into fat and stored in the body, leading to obesity. Exercise can increase fat breakdown, and long-term adherence to moderate exercise has a good effect on preventing obesity. Exercise is divided into aerobic exercise and anaerobic exercise. Aerobic exercise is characterized by high frequency, low intensity and long duration, such as walking and jogging. Anaerobic exercise is characterized by short duration and high intensity, such as weightlifting and fast running. Skeletal muscle metabolism plays an important role in regulating fat metabolism. Skeletal muscle can consume a large amount of fat, and a high fat consumption rate is a protective factor against weight gain and re-weight gain; conversely, a high carbohydrate consumption rate is a risk factor for weight gain and re-weight gain. Skeletal muscle exercise is the determining factor of energy consumption and fat breakdown. Appropriate physical activity can increase energy consumption and fat oxidation and decomposition, thereby fundamentally reducing the accumulation of fat in the body. (3) Social environment: The social environment also has a great influence on the occurrence of obesity. First of all, the social and family economic level. In poor and backward countries, people do not have enough to eat, and only a few people are obese. With the improvement of the social economic level, the number of obese people gradually increases. In our country, the same is true. When the country is prosperous, being fat is a symbol of "wealth". The Tang Dynasty is a typical example. In a sense, obesity is a byproduct of social prosperity. (4) Geographical environment: Geographical environment also affects the incidence of obesity. People in subtropical regions have to work all year round and suffer from the hot climate. They consume a lot of energy and their appetite is affected, so there are very few obese people. People in or near cold regions do not work in winter. The cold climate increases their hunger. They often drink alcohol and have meals together, so obesity is very common. People in mountainous areas have a lot of activity. Compared with people in plains, there are fewer obese people. The incidence of obesity is lower in resource-poor areas than in resource-rich areas. People's customs and traditional consciousness also affect the occurrence of obesity. After southerners settled in the north, they gradually adapted to local customs, and the number of obese people increased. Asians who migrated to the United States had higher rates of obesity and diabetes than their native compatriots. (5) Environmental endocrine disruptors: Many environmental endocrine disrupting chemicals (EECs) promote obesity, including bisphenol A (BPA), phthalic acid, dioxin analogs, and polychlorinated biphenyls (PCBs), whose mechanisms are related to estrogen-like effects. Most EECs belong to the class of environmental estrogens, which exert their effects in the body through the activation of estrogen receptors (ERs). Among them, ERα and ERβ are two major receptors that regulate the biological effects of estrogen. Early exposure to BPA can specifically alter the mRNA levels of ERα and ERβ, accelerating adipocyte differentiation and fat synthesis, leading to long-term obesity. Another major class is nuclear receptors. Peroxisome proliferation-activating receptor (PPAR) has been proven to be the main receptor regulating adipogenesis, and PPAR is considered a key regulator of adipogenesis. After PPAR and retinoid X receptor (RXR) form a heterodimer, they bind to PPAR response elements to regulate the expression of target genes at the transcriptional level. EDCs are a class of excellent peroxisome proliferators that can act as PPAR enzyme agonists to directly regulate gene activity at multiple stages of adipocyte differentiation by activating PPAR and RXR, leading to adipogenesis and accumulation.