1. Parasitic infection: The stomach is probably caused by intestinal parasitic infection. Parasites will absorb the nutrition of dogs, leading to emaciation, but the stomach will swell because of the existence of parasites.
2. Malnutrition: Dogs may not get enough nutrition, resulting in thin body, but their stomachs become bigger due to overeating.
3. Digestive problems: Dogs may have digestive problems, resulting in food not being fully absorbed, which leads to thin body, but because food stays in the digestive system, the stomach becomes bigger.
4. Intestinal diseases: Dogs may suffer from intestinal diseases, such as inflammatory bowel disease or intestinal obstruction, which causes food to fail to pass through the intestine normally, resulting in a bigger stomach and thinner body.