Table 2.
Characteristics of the included systematic reviews
| A) Systematic reviews with meta-analysis | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Author, year | Study type, study period | Study population | Exposition | Protein intake | Outcome | Effect estimates RR (95% CI) | Heterogeneity estimators | NutriGrade rating | AMSTAR 2 rating |
| Shin 2023 [13] |
- Published before 12/2022 - Follow-up: 7.4 yr |
- Only females - age NP |
High vs. low protein intake |
> 12.8 vs. ≤ 4.87 g/d Dietary assessment methods NP |
Breast cancer | Moderate | |||
| 1 cohort study |
n = 73,223 participants n = 592 cases |
Soy protein | 0.89 (0.67,1.17)1 | I2 = 0% | NA | ||||
|
Alzahrani 2022 [14] |
- Published before 10/2021 - Follow-up: 3.5–18 yr |
- Only males - Aged 26–92 yr |
High vs. low protein intake |
Protein intake NP Dietary assessment methods: selfreported FFQ, selfreported food record, recall interview |
Prostate cancer | Moderate | |||
| 8 cohort studies |
n = 214,276 participants n = 12,567 cases |
Total protein | 90.0–128.7 g/d vs. 38.0–82.0 g/d | 0.99 (0.92, 1.07)2 |
I2 = 12.8% P = 0.33 |
Low: 4.9 | |||
| 7 cohort studies |
n = 204,060 participants n = 7314 cases |
Dose–response analysis: 0.99 (0.98, 1.01) per 20 g/d increase Pnon-linearity = 0.51 |
I2 = 0% P = 0.43 |
||||||
| 6 cohort studies |
n = 324,197 participants n = 26,207 cases |
Animal protein | 62.8–80 g/d vs. 8.5–47 g/d | 0.99 (0.95, 1.04) |
I2 = 0% P = 0.94 |
Low: 5.9 | |||
| 5 cohort studies |
n = 313,981 participants n = cases |
Dose–response analysis: 1.00 (0.98, 1.01) per 20 g/d increase Pnon-linearity = 0.34 |
I2 = 25.5% P = 0.25 |
||||||
| 6 cohort studies |
n = 329,082 participants n = 26,137 cases |
Plant protein | 27.9–47.0 g/d vs. 13.0–29.0 g/d | 1.01 (0.96, 1.06) |
I2 = 0% P = 0.63 |
Low: 4.9 | |||
| 4 cohort studies |
n = 304,866 participants n = 20,704 cases |
Dose–response analysis: 1.01 (0.98, 1.04) per 20 g/d increase Pnon-linearity = 0.81 |
I2 = 0% P = 0.57 |
||||||
| 4 cohort studies |
n = 167,489 participants n = 9,864 cases |
Dairy protein | 20.5–27.0 g/d vs. 6.3–10.0 g/d | 1.08 (1.00, 1.16) |
I2 = 38.1% P = 0.16 |
Moderate: 6.0 | |||
| 3 cohort studies |
n = 157,273 participants n = 4611 cases |
Dose–response analysis: 1.10 (1.02, 1.20) per 20 g/d increase "Dairy protein intakes from 30 g/d to higher amounts were associated with a higher risk of prostate cancer, while this association for the intakes of < 30 g/d was not significant." Pnon-linearity = 0.02 |
I2 = 42.5% P = 0.17 |
||||||
| Fan 2022 [15] |
- Published before 09/2021 - Follow-up: 5.2–14 yr |
- Both sexes - Aged 40–74 yr |
High vs. low protein intake |
Protein intake NP Dietary assessment methods: 77-item validated FFQ, 81-item validated FFQ, 45-item validated FFQ, 165-item validated FFQ |
Overall cancer incidence | Moderate | |||
| 6 cohort studies |
n = 349,158 participants n = 1,970 cases |
Soy protein | 0.95 (0.71, 1.28)1 |
I2 = 68.9% P = 0.007 |
Low: 4.3 | ||||
|
Zhang 2022 [16] |
- Published before 10/2019 - Follow-up: NP |
- Both sexes - Aged 34–89 yr |
High vs. low protein intake |
Protein intake NP Dietary assessment methods: FFQ, validated FFQ |
Pancreatic cancer | Low | |||
| 2 cohort studies |
n = 77,156 participants n = 217 cases |
Total protein | 0.98 (0.63, 1.54)1 |
I2 = 0% P = 0.758 |
Very low: 1.5 | ||||
| 2 cohort studies and 1 case–control study |
n = 78,134 participants n = 543 cases |
Animal protein | 1.37 (0.93, 2.01)1 |
I2 = 32.7% P = 0.226 |
Very low: 2.5 | ||||
| 2 cohort studies and 1 case–control study |
n = 78,134 participants n = 543 cases |
Plant protein | 0.78 (0.54, 1.14)1 |
I2 = 11.5% P = 0.323 |
Very low: 2.5 | ||||
|
Khodavandi 2020 [18] |
- Published before 11/2019 - Follow-up: 8.1–16 yr |
- Only females - Aged 25–84 yr |
High vs. low protein intake |
> 83.5 g/d vs. < 72.6 g/d Dietary assessment methods: baseline questionnaire with 55-food items, 126-item FFQ, center-specific dietary questionnaires (EPIC), FFQ (block) |
Ovarian cancer | Low | |||
| 4 cohort studies |
- n = 464,643 participants - n = 1,585 cases |
Total protein | 0.96 (0.88, 1.06)2 |
I2 = 0% P = 0.741 |
Low: 5.0 | ||||
|
Mao 2018 [19] |
- Published before 09/2017 - Follow-up: 3.5–18 yr |
- Only males - Aged 40–92 yr |
High vs. low protein intake |
Total protein: 90–121 g/d vs. 0–82 g/d Animal protein: 41–80 g/d vs. ≤ 47 g/d Plant protein: 35–47 g/d vs. ≤ 29 g/d Dietary assessment methods NP |
Prostate cancer | Low | |||
| 8 cohort studies |
n = 265,067 participants n = 5,860 cases |
Total protein | 1.080 (0.964, 1.209)1 |
I2 = 0% P = 0.670 |
Very low: 2.9 | ||||
| 4 cohort studies and 1 case–control study |
n = 220,916 participants n = 8,826 cases |
Animal protein | 1.001 (0.917, 1.092)1 |
I2 = 0% P = 0.891 |
Very low: 3.5 | ||||
| 4 cohort studies and 1 case–control study |
n = 234,462 participants n = 8,937 cases |
Plant protein | 0.986 (0.904, 1.076)1 |
I2 = 0% P = 0.556 |
Very low: 3.5 | ||||
|
Pang 2018 [20] |
- Published until 06/2018 - Follow-up: NP |
- Only females - Aged 18–87 yr |
High vs. low protein intake |
> 89.9 g/d vs. < 72.6 g/d Dietary assessment methods NP |
Ovarian cancer | Low | |||
| 2 cohort studies |
n = 63,275 participants n = 210 cases |
Total protein | 0.903 (0.679, 1.201)1 |
I2 = 27.9% P = 0.239 |
Very low: 2.5 | ||||
|
Lai 2017 [21] |
- Published until 12/2016 - Follow-up: NP |
- Both sexes - Aged 20–89 yr |
High vs. low protein intake |
115.9 g/d vs. 83.8 g/day dietary assessment methods: Semiquantitative FFQ, FFQ, |
Colorectal cancer | High | |||
| 3 cohort studies |
n = 680 cases number of participants: NP |
Total protein | 0.939 (0.730, 1.209)1 |
I2 = 0% P = 0.980 |
Low: 4.0 | ||||
| B) Systematic reviews without meta-analysis | ||||||||
|---|---|---|---|---|---|---|---|---|
| Author, year | Study type, study period | Study population | Exposition | Protein intake | Outcome | Results | NutriGrade rating | AMSTAR 2 rating |
| Ubago-Guisado 2021 [17] |
- Published until 05/2021 - Follow-up: 8.7 yr |
- Only males - Age NP |
High vs. low protein intake |
Protein intake NP Dietary assessment methods NP |
Prostate cancer | Moderate | ||
| 1 cohort study |
n = 142,520 participants n = 2727 cases |
Total protein | “Total protein intake was not positively associated with increased risk (HR 1.17 (0.96, 1.44)” | NA | ||||
| 1 cohort study |
n = 142,520 participants n = 2727 cases |
Dairy protein |
“Protein from dairy foods was significantly associated with an increased risk (HR 1.22 (1.07, 1.41)” “An increment of 35 g/d dairy protein was associated with an HR of 1.32 (1.01, 1.72)” |
NA | ||||
| Pedersen 2013 [22] |
- Published between 01/2000 and 12/2011 - Follow-up: 5.5–18 yr |
- Only females - Healthy - Aged 30–70 yr |
High vs. low protein intake |
Protein intake np Dietary assessment methods: 61-item ffq over the past year, 107-item ffq over the previous year |
Breast cancer | Moderate | ||
| 1 cohort study and 1 nested case–control study |
- n = 88,647 participants - n = 214 controls - n = 4,163 cases |
Total protein |
None of the two studies found statistically significant associations Between total, animal or plant protein and breast cancer risk |
Low: 4.0 | ||||
| 1 cohort study and 1 nested case–control study |
- n = 88,647 participants - n = 214 controls - n = 4,163 cases |
Animal protein | Low: 4.0 | |||||
| 1 cohort study and 1 nested case–control study |
- n = 88,647 participants - n = 214 controls - n = 4,163 cases |
Plant protein | Low: 4.0 | |||||
AMSTAR 2 A Measurement Tool to Assess Systematic Reviews, CI confidence interval, d day(s) FFQ Food-frequency questionnaire, NA not applicable, NP not provided, RR relative risk, yr year(s), HR hazard ratio
1random effect model
2fixed effect model