A total of 12,757 participants were enrolled in this study. Table 1 presents the clinical characteristics of the study population according to NAFLD status. There were 4,393 participants with NAFLD, among whom 2,769 (63.6%) were male. The mean age in the group with NAFLD was 47.0 ± 10.6 years, and the group without NAFLD had a mean age of 44.8 ± 11.6 years. The mean age, BMI, WC, AST, ALT, fasting glucose, GGT, total cholesterol, HDL-C, LDL-C, and triglycerides were significantly higher in the study population with NAFLD than in the group with normal liver sonography. The proportion of smokers was also higher in the study population with NAFLD.
Table 1
Characteristics of the study population
| NAFLD (+) | NAFLD (-) | p-value |
N | 4393 | 8429 | |
Male | 2769 (63.6) | 2532(30.1%) | < 0.001 |
Age (years) | 47.00 ± 10.61 | 44.82 ± 11.58 | < 0.001 |
BMI (kg/m2) | 25.31 ± 3.228 | 21.88 ± 2.637 | < 0.001 |
Waist circumference (cm) | 85.53 ± 8.873 | 74.47 ± 8.126 | 0.001 |
Fasting glucose (mg/dL) | 100.61 ± 17.99 | 92.76 ± 9.886 | < 0.001 |
AST (IU/L) | 30.10 ± 19.41 | 25.87 ± 16.19 | < 0.001 |
ALT (IU/L) | 34.02 ± 26.03 | 20.08 ± 14.70 | < 0.001 |
Alkaline phosphatase (IU/L) | 75.81 ± 20.67 | 66.93 ± 21.19 | 0.270 |
GGT (IU/L) | 33.68 ± 32.07 | 19.36 ± 21.22 | < 0.001 |
Total cholesterol (mg/dL) | 216.98 ± 36.97 | 204.78 ± 34.51 | < 0.001 |
HDL-cholesterol (mg/dL) | 52.43 ± 11.59 | 61.98 ± 13.18 | < 0.001 |
LDL-cholesterol (mg/dL) | 141.55 ± 29.70 | 126.33 ± 27.62 | < 0.001 |
Triglycerides (mg/dL) | 153.72 ± 75.60 | 97.60 ± 47.92 | < 0.001 |
Current smoker (%) | 823(20.1%) | 731(9.2%) | < 0.001 |
Current exercise (%) | 1395(33.5%) | 2646(30.3%) | < 0.001 |
Values are presented as the mean ± SD or number (percentage). BMI, body mass index; AST, aspartate aminotransferase; ALT, alanine aminotransferase; GGT, γ-glutamyl transferase. |
Figure 2 showed the fatty liver severity according to quartiles of TyG index, TyG-BMI, TyG-WC, and FLI. The higher the indices, the higher was the fatty liver grade for all indices. The increase in the fatty liver severity was more pronounced in the TyG-WC index and FLI measurements.
The ORs (95% CIs) for NAFLD according to the quartiles of each parameter are shown in Table 2. Compared to the lowest TyG quartile in all participants, the OR (95% CI) for NAFLD was 9.036 (7.763-10.517) in the highest quartile after adjusting for age, AST, ALT, SBP, DBP, smoking, and exercise. The TyG-BMI index OR (95% CI) for NAFLD was 26.275 (21.710-31.799), the TyG-WC index OR (CI) was 39.251 (31.304-49.215) for TyG-WC index, and the FLI OR (CI) was 38.937 (31.145-48.678). When stratified by gender, the ORs (95% CIs) for NAFLD in male participants were 5.691 (4.686-6.913) for TyG index, 12.870 (10.339-16.021) for TyG-BMI, 14.050 (11.014-17.923) for TyG-WC, and 15.692 (12.078-20.387) for FLI. Similar results were observed in female participants: 8.659 (6.874-10.908) for TyG index, 21.353 (16.1340-28.259) for TyG-BMI, 26.379 (19.220-36.205) for TyG-WC, and 22.518 (16.979-29.864) for FLI.
Table 2
Odds ratios for NAFLD according to quartiles of each parameter.
| All subjects | Male | Female |
| Q1 | Q2 | Q3 | Q4 | Q1 | Q2 | Q3 | Q4 | Q1 | Q2 | Q3 | Q4 |
TyG index | | | | | | | | | | | | |
Unadjusted | 1 | 2.422 (2.102-2.791) | 5.313 (4.643-6.079) | 18.150 (15.841-20.794) | 1 | 2.098 (1.784-2.467) | 4.280 (3.634-5.039) | 9.322 (7.815-11.120) | 1 | 2.188 (1.723-2.779) | 4.385 (3.509-5.479) | 13.646 (11.020-16.899) |
Adjusted | 1 | 2.048 (1.759-2.384) | 3.652 (3.153-4.230) | 9.036 (7.763-10.517) | 1 | 1.812 (1.523-2.156) | 3.315 (2.777-3.957) | 5.691 (4.686-6.913) | 1 | 1.881 (1.461-2.421) | 3.507 (2.768-4.443) | 8.659 (6.874-10.908) |
TyG-BMI | | | | | | | | | | | | |
Unadjusted | 1 | 3.493 (2.919-4.181) | 12.450 (10.515-14.742) | 49.701 (41.819-59.069) | 1 | 2.889 (2.431-3.434) | 6.943 (5.833-8.265) | 22.089 (18.080-26.987) | 1 | 2.228 (1.658-2.994) | 6.559 (5.019-8.570) | 30.635 (23.652-39.680) |
Adjusted | 1 | 3.057 (2.528-3.697) | 9.067 (7.556-10.880) | 26.275 (21.710-31.799) | 1 | 2.477 (2.069-2.965) | 5.248 (4.364-6.310) | 12.870 (10.339-16.021) | 1 | 2.041 (1.493-2.789) | 5.410 (4.066-7.198) | 21.353 (16.134-28.259) |
TyG-WC | | | | | | | | | | | | |
Unadjusted | 1 | 3.733 (3.047-4.574) | 14.018 (11.580-16.971) | 60.054 (49.396-73.011) | 1 | 2.745 (2.274-3.313) | 8.022 (6.634-9.701) | 23.563 (18.975-29.261) | 1 | 2.360 (1.704-3.267) | 6.295 (4.676-8.474) | 34.604 (25.987-46.079) |
Adjusted | 1 | 3.638 (2.930-4.518) | 11.936 (9.673-14.727) | 39.251 (31.304-49.215) | 1 | 2.466 (2.020-3.011) | 6.311 (5.143-7.793) | 14.050 (11.014-17.923) | 1 | 2.243 (1.589-3.166) | 5.602 (4.070-7.711) | 26.379 (19.220 -36.205) |
FLI | | | | | | | | | | | | |
Unadjusted | 1 | 3.655 (2.986-4.474) | 14.263 (11.796-17.248) | 58.953 (48.542-71.597) | 1 | 3.108 (2.566-3.766) | 8.371 (6.940-10.098) | 27.765 (22.078-34.918) | 1 | 1.658 (1.211-2.270) | 5.152 (3.910-6.788) | 28.139 (21.622-36.618) |
Adjusted | 1 | 3.495 (2.823-4.326) | 12.494 (10.172-15.346) | 38.937 (31.145-48.678) | 1 | 2.875 (2.352-3.515) | 6.645 (5.426-8.139) | 15.692 (12.078-20.387) | 1 | 1.480 (1.065-2.058) | 4.735 (3.549-6.317) | 22.518 (16.979-29.864) |
Values are presented as the odds ratio (95% confidence interval). Adjusted for age, AST, ALT, SBP, DBP, smoking status, and exercise status. |
The predictability of NAFLD through WC, BMI, TyG, TyG-BMI, TyG-WC, and FLI are compared in Table 3 by areas under the ROC curves, illustrated in Figure3. The AUC was 0.805 (0.797-0.813) for BMI, 0.823 (0.815-0.831) for WC, 0.780 (0.771-0.789) for TyG index, 0.840 (0.832-0.847) for TyG-BMI, 0.848 (0.840-0.855) for TyG-WC, and 0.850 (0.842-0.857) for FLI. The AUC of TyG-WC and FLI were not statistically different with the post-hoc p-value of 0.1621, and TyG-WC and FLI showed better predictability for NAFLD compared to other indices.
Table 3
Areas under the ROC curves for each parameter for predicting NAFLD
Parameters | AUC (95% CI) | Overall p-value | Post hoc p-value | | |
All subjects | | | | | | | |
BMI | 0.805 (0.797-0.813) | < 0.0001 | Ref | | | | |
WC | 0.823 (0.815-0.831) | < 0.0001 | Ref | | | |
TyG index | 0.780 (0.771-0.789) | < 0.0001 | < 0.0001 | Ref | | |
TyG-BMI | 0.840 (0.832-0.847) | < 0.0001 | < 0.0001 | < 0.0001 | Ref | |
TyG-WC | 0.848 (0.840-0.855) | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 | Ref |
FLI | 0.850 (0.842-0.857) | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 | 0.1621 |
Male | | | | | | | |
BMI | 0.744 (0.731-0.758) | | Ref | | | | |
WC | 0.762 (0.749-0.776) | | < 0.0001 | Ref | | | |
TyG index | 0.728 (0.714-0.743) | < 0.0001 | < 0.0001 | < 0.0001 | Ref | | |
TyG-BMI | 0.788 (0.775-0.800) | < 0.0001 | < 0.0001 | < 0.0001 | Ref | |
TyG-WC | 0.798 (0.786-0.811) | < 0.0001 | < 0.0001 | < 0.0001 | 0.0014 | Ref |
FLI | 0.800 (0.787-0.812) | < 0.0001 | < 0.0001 | < 0.0001 | 0.0001 | 0.618 |
Female | | | | | | | |
BMI | 0.791 (0.777-0.804) | | Ref | | | | |
WC | 0.804 (0.791-0.817) | | 0.0008 | Ref | | | |
TyG index | 0.766 (0.752-0.781) | <0.0001 | 0.0040 | < 0.0001 | Ref | | |
TyG-BMI | 0.827 (0.814-0.839) | < 0.0001 | < 0.0001 | < 0.0001 | Ref | |
TyG-WC | 0.836 (0.823-0.848) | < 0.0001 | < 0.0001 | < 0.0001 | 0.0036 | Ref |
FLI | 0.834 (0.822-0.847) | < 0.0001 | < 0.0001 | < 0.0001 | 0.0053 | 0.5569 |
AUC, area under the curve; BMI, body mass index; WC, waist circumference; TyG, triglyceride and glucose; FLI, fatty liver index. |