Screening criteria for differential metabolites: select metabolites with fold change ≥ 2 and fold change ≤ 0.5. If the difference in metabolites between the control group and the experimental group is more than 2 times or less than 0.5, the difference is considered significant. If there is biological duplication in the sample grouping, on the basis of the above, select the metabolites with VIP≥1. The VIP value represents the influence of the difference between the corresponding metabolites in the classification and discrimination of the samples in each group in the model. It is generally considered that the metabolites with VIP≥1 are significantly different.