Characteristics of included studies
| First author [ref.], year | Country | Study design | Total subjects | Age of participants years | How COPD was diagnosed | Outcomes of interest | Factors adjusted for in analysis | Dietary patterns investigated |
| Ardestani [22], 2017 | Iran | Case–control | 164 | Mean 57 | Spirometric (FEV1/FVC <0.70 or FEV1 <80% pred) | OR, FEV1, FVC, FEV1/FVC | Unadjusted | DASH (H) |
| Brigham [62], 2018 | USA | Cohort | 15 256 | Mean 54.2 | Spirometric (FEV1 and FEV1/FVC <LLN) | PR, FEV1, FVC, FEV1/FVC | Age, sex, race, education, study location, smoking (status and pack-years), physical activity, total energy intake, BMI | Western (U), prudent (H) |
| Fischer [36], 2019 | Sweden | Case–control | 1802 | Mean 55 | Doctor diagnosis | OR | Higher education, living alone, number of daily cigarettes | Mediterranean (H) |
| Maisonneuve [20], 2016 | Italy | Cohort | 4336 | Median 57 | Radiological (CT) | OR | Age, sex, smoking duration, smoking intensity, years of smoking cessation, asbestos exposure, total energy | Mediterranean (H) |
| McKeever [19], 2010 | Netherlands | Cross-sectional | 12 648 | Range 20–59 | Spirometric (GOLD stage ≥2) | OR | Age, sex, age squared, height, age×height, smoking status, pack-years, BMI, educational level | Cosmopolitan (H), traditional (U), refined-foods (U) |
| Ogunmoroti [18], 2016 | USA | Cohort | 6506 | Mean 62.0 | Doctor diagnosis (discerned through ICD-9 codes) | HR | Age, sex, race/ethnicity, education, income | AHA criteria (H) |
| Shaheen [21], 2010 | UK | Cohort | 2942 | Mean 65.7 males, 66.6 females | Spirometric (FEV1/FVC <LLN) | OR | Age, height, smoking status, pack-years, smoke in home, age left education, home ownership, number of rooms, cars, social class, fat mass, activity score, energy intake, alcohol, dietary supplement use, birth weight, father's social class at birth, inhaled or oral steroid use, paracetamol use | Prudent (H) |
| Steinemann [63], 2018 | Switzerland | Cohort | 2178 | Mean 58.6 | Spirometric (FEV1/FVC<0.70) | OR | Study site, sex, age, height, smoking status, pack-years, number of daily cigarettes, exposure to passive smoking in the last 12 months, parental smoking in childhood, educational level, civil status, employment status, physical activity, total energy intake, BMI | Prudent (H), high-carbohydrate (U), Western (U) |
| Varasso [16], 2007 | USA | Cohort | 42 917 | Range 40–75 | Doctor diagnosis and spirometry or radiology (CXR or CT) | RR | Age, energy intake, smoking status, pack-years, race/ethnicity, physician visits, US region, BMI, physical activity, multivitamin use | Prudent (H), Western (U) |
| Varasso [37], 2007 | USA | Cohort | 72 043 | Range 30–55 | Doctor diagnosis and spirometry or radiology (CXR or CT) | RR | Age, smoking status, pack-years, exposure to second-hand tobacco smoke, menopausal status, race/ethnicity, spouse's educational attainment, physician visits, US region, physical activity, multivitamin use, energy intake | Prudent (H), Western (U) |
| Varasso [17], 2015 | USA | Cohort | 120 254 | Range 40–75 males, 30–55 females | Doctor diagnosis and spirometry or radiology (CXR or CT) | HR | Age, physical activity, BMI, total energy intake, smoking status, pack-years, second-hand tobacco exposure, race/ethnicity, physician visits, US region, spouse, highest educational attainment, menopausal status | Alternate Healthy Eating Index (H) |
| Voortman [38], 2017 | Netherlands | Cohort | 9701 | Median 64.1 | Spirometric (FEV1/FVC <0.70) or doctor diagnosis | HR | Age, subcohort, sex, smoking status, education level, employment status, total energy intake, physical activity, BMI | Dutch Dietary Guidelines (H) |
FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; LLN: lower limit of normal; CT: computed tomography; GOLD: Global Initiative for Chronic Obstructive Lung Disease; ICD-9: International Classification of Diseases, ninth revision; CXR: chest radiography; PR: prevalence ratio; HR: hazard ratio; RR: risk ratio; BMI: body mass index; DASH: Dietary Approaches to Stop Hypertension; H: healthy; U: unhealthy; AHA: American Heart Association; AHEI: Alternative Healthy Eating Index.