One of the main factors is metabolism. People with fast and good metabolism are able to burn calories more efficiently. This allows them to stay slim even when eating a significant amount.

People with an ideal body weight tend to have a healthy eating pattern. They choose low-fat, high-fiber, and nutrient-rich foods. In doing so, even though they eat a lot, they still pay attention to the nutrients contained in the food.

Genetics plays a crucial role in determining a person's body shape. Some individuals may have a genetic tendency to stay slim even when consuming large amounts of food.

Hormonal balance in the body can affect metabolism and nutrient absorption. People who stay slim may have good hormonal balance.