Final answer:
Really skinny people not gaining weight despite eating a lot can be due to metabolic rates, genetic factors, levels of physical activity, and body set point. Metabolic rate is a key factor that determines how our bodies use energy, and genetic predispositions can influence how we process and store food. Eating disorders can also affect body weight and are characterized by abnormal eating habits and attitudes towards food and weight.
Step-by-step explanation:
Really skinny people eating as much as big people but not gaining weight is an example of differences in metabolism, genetics, levels of physical activity (or inactivity), and the concept of the body's set point, which is the weight range that your body is predisposed to maintain. Each person's metabolism works at a different rate, which can explain why two individuals with the same diet and calorie intake might have very different body weights. Genetic factors play a significant role in determining our metabolic rate and how our bodies process food and store fat.
Moreover, someone's inactivity or physical activity levels can greatly impact their energy balance. While excessive energy consumption coupled with little energy use can lead to obesity, others may maintain a low body weight despite high caloric intake due to higher energy expenditure.
Additionally, eating disorders like anorexia nervosa and binge eating disorder can contribute to the body weight differences among individuals. Anorexia nervosa involves eating very little and having a fear of gaining weight, often coupled with a distorted body image. In contrast, binge eating disorder involves periods of excessive eating without the compensatory purging, which can lead to weight gain.