Due to long-term evolution, most carnivores such as tigers and lions are mainly carnivorous. It is not easy for them to survive in the wild. For example, if they want to capture a large animal that can be eaten, some need to work together to round up (such as a lion), and the prey is divided among everyone, so that most individuals will not gain much; some need to wait and follow for a long time (such as a tiger), and when the hunting is successful, they will be hungry; some need to run quickly and chase with all their strength (such as a cheetah), and often end in failure. Even if these wild animals eat meat and bones, the energy converted by the nutrients they consume is consumed a lot during the predation process, and not much energy can be converted into fat and stored. Therefore, these carnivores do not gain weight.
The so-called fat, the scientific language is the accumulation of fat in the body. Animals such as tigers and lions consume a lot of physical energy when looking for, rounding up, or waiting for and tracking prey, so they are unlikely to accumulate large amounts of fat. The pigs we talk about refer to livestock pigs. Under the care of humans, the pigs do nothing all day long, have sufficient food and rich nutrients, and have limited space in the pigsty and little activity. In this way, if you consume more nutrients and consume less, body fat will gradually accumulate. Now that some pigs are stocked, a lot of fat will not accumulate in their bodies. In fact, wild boars living in the wild are not fat. In order to find food, the wild boar has to constantly run and search in the forest. They get limited food in the wild, but consume a lot of energy. Of course, there is no excess energy to be converted into fat.