Table 1.
Characteristics and quantitative synthesis of the eligible meta-analyses of DII for health outcomes.
| Outcomes (reference) | First author, year | Study design included in meta-analysis | No. of studies | No. of cases/participants | Level of comparison | Summary effect size (95% CI) | |
|---|---|---|---|---|---|---|---|
| Random effects | Fixed effects | ||||||
| Cancer outcomes | |||||||
| Breast and prostate cancer (26) | Moradi S, 2018 | Cohort and Case–control study | 9 | 9,972/52,203 | Highest vs. lowest | 1.70 (1.31–2.22) | 1.40 (1.27–1.55) |
| Breast cancer (30) | Liu, 2019 | Cohort and Case–control study | 12 | 30,052/347,147 | Highest vs. lowest | 1.34 (1.14–1.56) | 1.19 (1.14–1.24) |
| Breast cancer (31) | Jayedi A, 2018 | Cohort and Case–control study | 7 | 18,781/225,606 | A 1-unit increment | 1.04 (1.00–1.08) | 1.01 (1.00–1.02) |
| Colon cancer (25) | Zhang, 2017 | Cohort and Case–control study | 6 | 8,210/389,847 | Highest vs. lowest | 1.37 (1.16–1.62) | 1.26 (1.18–1.36) |
| Colorectal cancer (37) | Moazzen S, 2020 | Cohort and Case–control study | 11 | 28,645/1,037,658 | Highest vs. lowest | 0.66 (0.56–0.78) | 0.79 (0.75–0.83) |
| Colorectal cancer (31) | Jayedi A, 2018 | Cohort and Case–control study | 9 | 18,888/878,912 | A 1-unit increment | 1.06 (1.04–1.09) | 1.04 (1.01–1.05) |
| Digestive tract cancer (24) | Zahedi H, 2020 | Cohort and Case–control study | 14 | 15,399/694,894 | Highest vs. lowest | 1.83 (1.53–2.19) | 1.29 (1.23–1.35) |
| Esophageal cancer (34) | Li, 2018 | Cohort and Case–control study | 5 | 891/3,598 | Highest vs. lowest | 2.81 (2.07–3.82) | 2.74 (2.11–3.57) |
| Gastric cancer (36) | Liang, 2019 | Cohort and Case–control study | 3 | 700/2,118 | Highest vs. lowest | 2.12 (1.41–3.18) | 1.95 (1.48–2.57) |
| Gastric cancer (36) | Liang, 2019 | Cohort and Case–control study | 3 | 475/101,835 | A 1-unit increment | 1.45 (1.04–2.03) | 1.24 (1.12–1.38) |
| Gynecological cancers (30) | Liu, 2019 | Cohort and Case–control study | 18 | 33,907/357,095 | Highest vs. lowest | 1.38 (1.21–1.56) | 1.21 (1.16–1.26) |
| Hormone-dependent cancer (24) | Zahedi H, 2020 | Cohort and Case–control study | 14 | 22,234/239,666 | Highest vs. lowest | 1.22 (1.10–1.34) | 1.10 (1.06–1.15) |
| Larynx cancer (35) | Hua, 2020 | Case–control study | 3 | 997/2,805 | Highest vs. lowest | 2.05 (0.85–4.93) | 2.67 (1.95–3.66) |
| Lung cancer (34) | Li, 2018 | Cohort and Case–control study | 6 | 2,162/7,707 | Highest vs. lowest | 1.56 (1.21–2.01) | 1.45 (1.22–1.73) |
| Oral cavity cancer (35) | Hua, 2020 | Case–control study | 3 | 926/3,371 | Highest vs. lowest | 2.23 (1.73–2.86) | 2.23 (1.73–2.86) |
| Overall cancer (34) | Li, 2018 | Cohort and Case–control study | 44 | 48,032/1,298,343 | Highest vs. lowest | 1.58 (1.45–1.72) | 1.37 (1.32–1.42) |
| Overall cancer (34) | Li, 2018 | Cohort and Case–control study | 30 | 31,863/532,225 | A 1-unit increment | 1.13 (1.09–1.16) | 1.08 (1.07–1.10) |
| Ovarian cancer (30) | Liu, 2019 | Cohort and Case–control study | 4 | 3,104/7,982 | Highest vs. lowest | 1.41 (1.21–1.65) | 1.41 (1.21–1.65) |
| Pharynx cancer (35) | Hua, 2020 | Case–control study | 4 | 1,161/9,163 | Highest vs. lowest | 2.02 (1.54–2.64) | 2.00 (1.59–2.51) |
| Prostate cancer (32) | Zhu, 2019 | Cohort and Case–control study | 10 | 5,326/52,873 | Highest vs. lowest | 1.73 (1.34–2.23) | 1.28 (1.17–1.39) |
| Prostate cancer (32) | Zhu, 2019 | Cohort and Case–control study | 10 | 5,326/52,873 | A 1-unit increment | 1.10 (1.04–1.17) | 1.04 (1.02–1.07) |
| Rectal cancer (25) | Zhang, 2017 | Cohort and Case–control study | 7 | 4,679/730,773 | Highest vs. lowest | 1.44 (1.23–1.69) | 1.42 (1.29–1.57) |
| Respiratory tract cancer (24) | Zahedi H, 2020 | Cohort and Case–control study | 4 | 1,261/41,979 | Highest vs. lowest | 1.80 (1.21–2.67) | 1.74 (1.40–2.16) |
| UADT cancer (35) | Hua, 2020 | Case–control study | 9 | 4,394/19,984 | Highest vs. lowest | 2.27 (1.89–2.73) | 1.93 (1.78–2.10) |
| Mortality | |||||||
| All-cause mortality (29) | Namazi N, 2018 | Cohort and Cross-sectional study | 6 | 32,677/107,306 | Highest vs. lowest | 1.21 (1.09–1.35) | 1.13 (1.09–1.18) |
| Cancer mortality (24) | Zahedi H, 2020 | Cohort and Case–control study | 11 | 9,506/229,115 | Highest vs. lowest | 1.23 (1.07–1.42) | 1.14 (1.07–1.22) |
| CVD mortality (27) | Ji, 2020 | Cohort study | 10 | 32,319/385,765 | Highest vs. lowest | 1.31 (1.19–1.44) | 1.21 (1.16–1.27) |
| CVD mortality (9) | Shivappa N, 2017 | Cohort and Cross-sectional study | 6 | 11,094/93,866 | A 1-unit increment | 1.09 (1.03–1.15) | 1.06 (1.04–1.08) |
| Metabolic outcomes | |||||||
| Central obesity (38) | Farhangi MA, 2020 | Cross-sectional study | 10 | 6,904/25,435 | Highest vs. lowest | 1.16 (0.95–1.43) | 1.06 (0.96–1.17) |
| Hypertension (33) | Farhangi MA, 2019 | Cross-sectional study | 12 | 20,126/44,102 | Highest vs. lowest | 1.13 (1.01–1.27) | 1.15 (1.08–1.23) |
| Hyperglycemia (33) | Farhangi MA, 2019 | Cross-sectional study | 9 | 5,365/10,715 | Highest vs. lowest | 1.13 (0.95–1.35) | 1.05 (0.95–1.16) |
| Metabolic syndrome (29) | Namazi N, 2018 | Cohort and Cross-sectional study | 5 | 2,242/15,161 | Highest vs. lowest | 1.01 (0.82–1.24) | 1.01 (0.87–1.18) |
| Other outcomes | |||||||
| CVD (27) | Ji, 2020 | Cohort study | 6 | 1,310/43,385 | Highest vs. lowest | 1.41 (1.12–1.78) | 1.35 (1.13–1.61) |
| CVD (9) | Shivappa N, 2017 | Cohort and Cross-sectional study | 4 | 2,420/49,446 | A 1-unit increment | 1.08 (1.00–1.16) | 1.03 (1.01–1.05) |
| Depression (28) | Wang, 2018 | Cohort and Cross-sectional study | 6 | 4,864/49,584 | Highest vs. lowest | 1.23 (1.12–1.35) | 1.23 (1.12–1.35) |
CVD, cardiovascular disease; DII, dietary inflammatory index; UADT, upper aerodigestive tract.