Table 1 presented the demographic characteristics among NGT, IGT, and T2DM groups. A total of 9082 participants, 6892 participants with NGT, 765 participants with T2DM, and 1434 participants with IGT, were finally included in this study. Participants in T2DM and IGT groups tended to be older with larger BMI than those in the NGT group (P < 0.05). IGT and T2DM individuals had lower education, less smoking, and more hypertension and were less likely to exercise compared with NGT individuals (P < 0.05).

The average FA intakes and the difference between T2DM, IGT, and NGT groups are summarized in Table 2. The dietary intakes of total FA (TFA), total saturated FA (TSFA), monounsaturated FA (MUFA), and polyunsaturated FA (PUFA) were included in the study. Among them, the intakes of TFA, MUFA, and PUFA were statistically lower in IGT and T2DM groups than those in the NGT group (P < 0.05). The average intake of TSFA and SFA subtypes in the IGT group was significantly lower than that in T2DM and NGT groups, including butanoic acid (4:0), hexanoic acid (6:0), octanoic acid (8:0), decanoic acid (10:0), dodecanoic acid (12:0), tetradecanoic acid (14:0), hexadecanoic acid (16:0), and octadecanoic acid (18:0). Among MUFAs, hexadecenoic acid (16:1), octadecenoic acid (18:1), and eicosenoic acid (20:1) were statistically lower in T2DM and IGT groups than those in the NGT group. Among PUFAs, octadecadienoic acid (18:2) and octadecatrienoic acid (18:3) were statistically lower in T2DM and IGT groups than those in the NGT group. There was no statistical difference in the remaining FAs among the three groups.

The correlation between FA intake and the risk of IGT and T2DM is indicated in Table 3. In model 1, a negative correlation was observed between dietary TFA and the risk of IGT (odds ratio [OR] = 0.996, 95% confidence interval [CI]: 0.994–0.999, P = 0.008). A negative correlation was also observed between TSFA and MUFA with the risk of IGT (OR = 0.989, 95% CI: 0.983–0.999, P < 0.001; OR = 0.992, 95% CI: 0.987–0.998, P = 0.013). Among SFAs, all SFAs were negatively correlated with IGT except for hexanoic acid (6:0) and dodecanoic acid (12:0). Among MUFAs, hexadecenoic acid (16:1) and octadecenoic acid (18:1) were negatively correlated with the risk of IGT (OR = 0.850, 95% CI: 0.762–0.948, P = 0.010; OR = 0.991, 95% CI: 0.985–0.997, P = 0.012). Among PUFA, only octadecatrienoic acid (18:3) was negatively correlated with the risk of IGT (OR = 0.903, 95% CI: 0.835–0.977, P = 0.021). FAs with statistical significance in model 1 were included in model 2 for analysis. In model 2 and model 3, TSFA, octanoic acid (8:0), decanoic acid (10:0), tetradecanoic acid (14:0), octadecanoic acid (18:0), and octadecatrienoic acid (18:3) were negatively associated with the risk of IGT. However, no significant association between FAs and T2DM was observed.

The association of dietary intakes of TFA, TSFA, MUFA, and PUFA quartile ranges with the risk of IGT is demonstrated in Table 4. NGT and quartile 1(Q1) were used as the reference group. The quartile range of the average dietary intake of the participants is depicted in supplementary table 1. In model 1, most of the dietary FAs in the range of Q3 and Q4 were negatively correlated with the risk of IGT. However, in model 2, SFAs including butanoic acid (4:0), hexanoic acid (6:0), octanoic acid (8:0), decanoic acid (10:0), and tetradecanoic acid (14:0) were negatively correlated with the risk of IGT. Further adjusted covariates in model 3, hexanoic acid (6:0) at 0.239–0.407 g/day was negatively correlated with the risk of IGT (OR = 0.747, 95% CI: 0.638–0.965, P = 0.024). Similarly, octanoic acid (8:0) at 0.3255–6.101 g/day, decanoic acid (10:0) at 0.610–4.611 g/day, and tetradecanoic acid (14:0) at 2.803–18.669 g/day were negatively associated with the risk of IGT.

The association between FA quartile ranges and the risk of T2DM is demonstrated in Table 5. Contrasting the IGT, in the three models, TFA was negatively correlated with the risk of T2DM. Nevertheless, the association between TSFA, MUFA, PUFA, and their subtypes and the risk of T2DM were not statistically significant in model 1, model 2, and model 3. Therefore, to determine the combined FAs that are associated with IGT and T2DM, the data were further analyzed by factor analysis. Analysis of the scree plot revealed that four factors had eigenvalues greater than the average eigenvalue Supplementary Fig. 1. The four factors described 78.010% of the total variability in the provided set of predictors. The rotated component matrix is indicated in Supplementary Table 2. Factor (F) 1 better represented the effect of SFAs whereas F4 represented octadecenoic acid (18:1), eicosenoic acid (20:1), octadecadienoic acid (18:2), and octadecatrienoic acid (18:3). The association between four factors and the risk of IGT and T2DM are presented in Table 6. Among the participants with IGT, F1 was negatively associated with the risk of IGT in model 1 and model 2 (OR = 0.872, 95% CI: 0.801–0.948, P = 0.005; OR = 0.889, 95% CI: 0.815–0.970, P = 0.031). No similar results were observed in Model 3. F4 was negatively associated with the risk of T2DM in the three models.