The human body is a closed system that requires energy to maintain its basic functions, such as breathing, circulation, and digestion. This energy is obtained from our food, which is converted into calories that our body can use for fuel.
When we consume more calories than our body needs for these basic functions, the excess calories are stored as fat, which can lead to weight gain over time. Conversely, when we consume fewer calories than our body needs, the stored fat is used for energy, which can lead to weight loss.
This is the basic principle behind the concept of "calories in versus calories out" for weight loss. By consuming fewer calories and/or increasing physical activity to burn more calories, we create a calorie deficit that can lead to weight loss over time.
While it is true that some people may have a genetic predisposition to weight gain or loss, the majority of individuals can achieve a healthy weight through a balanced diet and regular physical activity. Moreover, studies have shown that the most effective way to lose and keep weight off is through a combination of diet and exercise.
In conclusion, while the concept of "calories in versus calories out" may be oversimplified at times, it remains a fundamental principle for weight loss and overall health. By consuming a healthy diet and engaging in regular physical activity, individuals can create a sustainable calorie deficit that can lead to long-term weight loss and improved health outcomes.
This is why when you're undernourished, you lose weight. People that can't lose weight are either skin and bones or in caloric excess.