All participants ingested the high-fat meal during the OFTT and it was well tolerated.
3.1 Basic characteristics
There were 472 participants in the present study, of whom 224 were male and 248 were female. The mean age of the men was 45±13 years old and that of the women was 44±13 years old (Table 1).
The participants were allocated to the two groups according to their liver ultrasonographic findings. The BMI, WC, systolic blood pressure, and diastolic blood pressure of the NAFLD group were higher than those of the control group (P<0.01). The FPG, FINS, TC, TG, LDL-C, ApoB, and HOMA-IR of the NAFLD group were higher than those of the control group (P<0.001). The HDL-C and ApoA1 concentrations and the ApoA1/ApoB ratio in the NAFLD group were lower than in the control group (P<0.001, P=0.001, and P<0.001, respectively) (Table 1).
The differences in the BMI, FBG, FINS, HOMA-IR, TC, TG, HDL-C, LDL-C ApoA1, ApoB, and ApoA1/ApoB of the NAFLD and control groups were affected by gender. The BMI, FBG, FINS, and HOMA-IR of male and female participants with NAFLD were higher than those of the same gender in the control group (P<0.001). The fasting TC, TG, and LDL-C concentrations in the NAFLD group were higher than those in the control group among participants of the same gender, but HDL-C was lower than that in the control group (P<0.05) (Table 2).
3.2 Circulating lipid concentrations at time points during the OFTT
The TC, TG, and LDL-C concentrations in the fasting state and 2 h, 4 h, 6 h, 8 h, and 10 h after the start of the OFTT were higher in the NAFLD group than in the control group, whereas the HDL-C concentrations were lower (P<0.001) (Table 3).
3.3 Triglyceride peak concentration and time
We next constructed a graph of the TG concentration at time points during the OFTT. The TG in each group increased gradually after the ingestion of the high-fat meal in OFTT. In the control group, the TG peaked at 4h postprandial and had returned to near the fasting concentration after 10 h. In contrast, the TG of the NAFLD group peaked 6h postprandially and had not returned to the fasting concentration by 10h postprandially ( Figure 1).
3.4 Comparison of parameters in groups with differing fasting triglyceride concentrations
According to their fasting triglyceride concentration, all the participants were allocated to one of two groups. Those with fasting TG concentrations ≤1.7 mmol/L were placed in the normal-triglyceride group (NFTG group) and those with TG >1.7 mmol/L were placed in the high fasting triglyceride group (HFTG group). The BMI, FBG, FINS, and HOMA-IR of the HFTG group were higher than those of the NFTG group (P<0.001). The incidence of NAFLD in our participants is 32.8%. Pearson’s chi-square test showed that the incidence of NAFLD in the HFTG group was higher than that in the NFTG group (P<0.001) (Table 4).
3.5 Risk factors for NAFLD
The effects of BMI, WC, TC, TG, FBG, FINS, HOMA-IR, HDL-C, LDL-C, and fat load on NAFLD were determined using binary logistic regression analysis, and the factors that influenced or protected against NAFLD were further clarified by the creation of a forest plot. The parameters that were shown to be associated with the prevalence of NAFLD were BMI, WC, TG, 2-h postprandial TG, 4-h postprandial TG, HDL-C, LDL-C, and HOMA-IR (Table 5, Model 1, Figure 2A). After adjusting age and gender, factors listed above are still associated with NAFLD (Table 5, Model 2, Figure 2B). In order to exclude the effect of fasting TG, we further adjusted age, gender and fasting TG, result showed that higher postprandial TG concentration still associated with higher risk of NAFLD (Table 5, Model 3, Figure 2C).
3.6 Characteristics of participants with differing levels of fat tolerance
The participants were allocated to three groups according to their fasting and 4-h postprandial TG concentrations. 4h postprandial triglyceride concentration higher than 2.5mmol/L was defined as high postprandial triglyceride (HTG) [26].
Those with normal fasting and postprandial TG concentrations were placed in the NFT group, those with normal fasting but HTG were placed in the impaired fat tolerance (IFT) group, and those with high fasting TG concentration were placed in the fasting hypertriglyceridemia (FHT) group.
Across the three groups, BMI, WC, FINS, HOMA-IR, TC, TG, and LDL-C all increased with decreasing fat tolerance, whereas HDL-C decreased with decreasing fat tolerance (P<0.05). The age and FPG of the IFT and FHT groups were higher than those of the NFT group (P<0.05), but there were no significant differences in age or FPG between the IFT and FHT groups. In addition, the incidence of NAFLD increased as the fat tolerance decreased (P<0.001) (Table 6).