Weight management is like an endless battle for most people. Many believe it simply requires strong willpower or better dietary choices. However, science shows the reality is far more complex. Ancient biology, our genes, and the external world interact in strange ways. It’s not as simple as eating less and exercising more. Understanding these deeper forces can change the way we view things.
Imagine talking to a geneticist who studies the basic building blocks of life. They might tell you that your genes determine how easily you gain weight. Reframing this understanding makes more sense, and we turn to biology for help. Genetics explains most of the natural variation in weight.
Our understanding of genes is largely derived from studies of twins. Identical twins share almost all of their genes, while fraternal twins share only about half of their genes. Researchers have studied the differences in characteristics between different types of twins and found that the heritability of body weight ranges from 40% to 70%.The heritability of height is believed to be mainly determined by genetic factors, at about 85%. The heritability of weight is not much different from that of height.
Genes influence the brain’s mechanism for processing the urge to eat, which scientists now refer to as “appetite.” Appetite itself involves three main concepts: hunger, satiety, and the pleasure derived from eating. Different areas of the brain are responsible for regulating these aspects.
Hunger signals primarily originate from the hypothalamus, located near the base of the midbrain. Satiety ranges from satisfied to completely full, with the posterior brain primarily managing this sensation.The pleasure derived from eating originates from higher brain regions, a dispersed area known as the pleasure center. These regions are closely interconnected and communicate with one another. Imagine them as three points on a triangle. Appetite is at the center of the triangle, and altering one point can change the shape of the entire appetite drive. External cues and internal signals constantly influence it.
Internal signals provide the brain with interesting information. The brain needs to constantly monitor the body’s condition. It needs to know the long-term energy reserves stored in the body, with fat stores being a key piece of information. This determines how long you can survive without eating. Additionally, the brain requires real-time updates from the gut. This information comes from recently consumed food, with both long-term and short-term signals having hormonal characteristics. These signals are transmitted through the bloodstream to the brain, where hormones then convey their specific information along specific pathways.
A key fat-sensing circuit involves the leptin-melanocortin pathway. Leptin is a hormone produced by fat cells, and its levels are directly related to the amount of fat in the body. The more fat there is, the more leptin protein is produced. This circuit is considered the most effective mechanism for sensing fat and regulating appetite, and mutations in the genes involved in this pathway are closely associated with appetite drive and obesity risk. This clearly demonstrates the powerful role of genetic factors in this process.
In addition to fat signals, many gut hormones continuously exert their effects. Hormones appear to be released with each meal, from the first bite to the complete expulsion of food from the body. Hormones also transmit information about calorie and nutrient content. They inform the brain about the levels of protein, fat, and carbohydrates. Remarkably, 18 out of 20 gut hormones make us feel fuller.Foods that take longer to digest trigger different hormones, significantly enhancing the feeling of fullness. High-protein foods are particularly effective at producing this effect. This helps explain why protein-rich diets work for some people. They enhance satiety, leading you to naturally eat less.
GLP-1 is a highly protein-sensitive intestinal hormone that significantly increases after meals. New anti-obesity drugs like Ozempic mimic this hormone; these drugs are modified versions of the natural GLP-1 protein. The problem with natural GLP-1 is that it has an extremely short half-life of only about two minutes.The ingenuity of the new drugs lies in their longer half-life. This allows the current version to be administered via weekly injections, with longer-acting options currently in rapid development.
Dieting often increases feelings of hunger, and these new GLP-1 drugs address this issue directly. They work by making you feel fuller, which helps maintain weight loss progress.
UK data clearly shows significant differences. The obesity rate among the lowest 20% income group is twice that of the highest income group, at 36% and 20%, respectively. This is not a small difference but a significant one.A twin study called the “Gemini cohort” further confirmed this association. The heritability of BMI was significantly higher in low-income groups, at 86% and 39%, respectively. Clearly, there is a strong interaction between environmental factors and genetic susceptibility.
This clearly demonstrates that the environment has a significant impact on genetic factors. If an individual carries obesity risk genes, exposure to cheap unhealthy foods will maximize this risk. A healthier environment can significantly reduce this genetic risk, and access to high-quality foods and fewer tempting cues is highly beneficial. This interaction explains the wide variability in BMI heritability, and the environment does indeed modify an individual’s genetic potential.Appetite is a finely tuned system that operates continuously. Hunger, satiety, and reward mechanisms interact to form a triangular relationship. Internal signals interact with external factors to drive or inhibit this system. This explains phenomena in our daily lives that we may not have noticed. For example, when we are hungry, even simple foods seem delicious. At this point, the reward circuit becomes active.
Today, being overweight may be a natural response. From certain perspectives, it may even be highly evolved.The core issue is our disconnect from an environment we once adapted to. In ancient times, food was often scarce and unpredictable, while the modern world is filled with high-calorie foods. Stimulating food cues are everywhere, and this clash between ancient programming and the current world has led to problems. It has pushed obesity into a major public health challenge, and to effectively address this complex issue, we must acknowledge the central role of genes in responding to the environment.
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