The Influence of Lifestyle, Social Factors, and Neuroendocrine Functions on Obesity

Smoking and Obesity: Smoking increases resting energy expenditure, therefore, under the same conditions, smokers tend to weigh less than non-smokers. A study by CADE et al. involving 2340 participants showed that smokers had lower BMIs than both non-smokers and those who had quit smoking, with men having the highest BMIs among quitters and men having the lowest. Previous research has shown that long-term smokers typically experience weight gain after quitting, with smokers on average weighing less than those who have quit, while the weight of never-smokers falls somewhere in between. The mechanisms underlying weight gain after quitting smoking are not yet fully understood.

This may be related to the following factors: ① Smoking increases resting energy expenditure; after quitting smoking, daily energy metabolism decreases. ② After quitting smoking, smokers often change their eating habits, increasing their intake of sweets and other sugary snacks, leading to increased daily energy intake. Lifestyle and Obesity: Technological advancements have changed people's lifestyles, bringing many conveniences, but also many negative impacts. For example, the widespread use of cars and televisions has reduced people's opportunities for physical activity, while increasing the time spent sitting and lying in bed.

Furthermore, increasingly fierce social competition and a faster pace of life mean people have less and less time to exercise, all of which significantly increase the likelihood of obesity. Education level and economic status are also directly related to obesity, with a particularly pronounced impact on women. In developed countries and regions, those with better education and economic status are more likely to recognize the negative impact of obesity on their appearance and health, and they have the resources and time for necessary physical exercise; therefore, their obesity rates are lower.

Conversely, those with poor education and lower economic status tend to have higher rates of obesity. In underdeveloped countries and regions, those with good education and higher economic status often have a higher incidence of obesity than those with poor education and lower economic status. This is because the former have access to sufficient or even excessive nutrition, while the latter are often struggling to make ends meet, and their energy intake is barely enough to sustain their energy expenditure. The hypothalamus and higher nervous activity: The satiety center is located in the ventromedial nucleus of the hypothalamus, while the feeding center is located in the ventrolateral nucleus of the hypothalamus. These two centers are connected by nerve fibers and functionally regulate and constrain each other.

Animal experiments have shown that these two centers are affected by the body's sugar, fat, and amino acids. Therefore, when there is hypothalamic lesion or certain metabolic changes in the body, the appetite center can be affected, leading to overeating and obesity. This is the main cause of hypothalamic syndrome. In simple obesity, functional changes in the hypothalamus are often considered. Higher neural activity in the cerebral cortex affects the hypothalamic appetite center through neurotransmitters, playing a role in regulating hunger and satiety. Psychological factors often affect appetite, and the function of the appetite center is subject to mental state.

When excessive mental stress stimulates the adrenergic nerves and excites the sympathetic nervous system, appetite is suppressed; conversely, when the vagus nerve is excited and insulin secretion increases, appetite increases. It is known that stimulation of the ventromedial nucleus of the hypothalamus promotes insulin secretion, thus increasing appetite; stimulation of the ventromedial nucleus inhibits insulin secretion and increases glucagon secretion, thus decreasing appetite. This indicates that higher nervous activity influences the hypothalamic appetite center and insulin secretion through the autonomic nervous system, leading to either polyphagia/obesity or anorexia/emaciation. Endocrine factors: Besides hypothalamic factors, imbalances in other endocrine hormones can also cause obesity.

Changes in insulin levels are widely recognized as the most crucial element in the mechanism of obesity, followed by changes in adrenocortical hormones. Insulin: Insulin is a hormone secreted by pancreatic beta cells. Its functions include promoting glycogen synthesis in hepatocytes and inhibiting gluconeogenesis; promoting glucose uptake and fat synthesis in adipocytes and inhibiting fat breakdown. The latter two functions are particularly important in the mechanism of obesity. The characteristics of insulin secretion in obese individuals are: ① Fasting baseline insulin levels are higher than normal or above normal. ② During an oral glucose tolerance test, plasma insulin levels rise further as blood glucose levels increase.

③ The peak plasma insulin level often lags behind the peak blood glucose level, thus hypoglycemia can occur 3-4 hours after a meal. Recent studies have also found that obese individuals have reduced insulin receptor numbers and affinity, exhibiting insulin insensitivity and resistance. Due to insulin insensitivity and resistance, insulin levels must be maintained at high levels to meet glucose metabolism needs. Hyperinsulinemia, however, increases fat synthesis and decreases fat breakdown in adipocytes and fat metabolism, further contributing to obesity. Once obese individuals lose weight to a normal range, plasma insulin levels and insulin receptors can return to normal, indicating that this change is secondary.