Mainly because of the special national conditions of the United States and the different eating habits of the rich and the poor. In the United States, animal farming is a large-scale mechanization, and with the scientific and reasonable management of the Agricultural Association, the cost is well controlled and the meat price is relatively low. Vegetables in America are basically organic vegetables, which are expensive to sell. America is a country where fast food is very popular. The poor tend to eat some cheap and full food, and fast food has become the best choice. Fast food is high in salt and fat, with more meat and less vegetables, and it is easy to be obese if eaten for a long time. Poor people are more likely to be obese because of their heavy life pressure and abnormal fat metabolism, and they don't pay much attention to their health. Rich people have money and time, like to pursue health and pay great attention to diet.