Table 2  Summary of 12 studies reporting an association between dietary patterns and asthma outcomes in adults
Studya and location  Sample and study design  Asthma outcome  Dietary pattern  Primary results  Adjusted confounders  Quality score (rating)b
Rosenkranz et al22Australia  n=156,035; male 62.2±10.6 years; female 60.2±10.2 years; 55% female; cross-sectional  Ever asthma  PCA: 4 dietary patterns for men (“fruit and vegetable”, “meats and cheese”, “grains and alcohol”, “poultry and seafood”) and 5 for women (“fruit and vegetables”, “meats”, “poultry and seafood”, “cereal and alcohol”, “brown bread and cheese”); 12-item FFQ  For men, a risk factor for asthma was meat/cheese (OR 1.18, 95% CI 1.08–1.28). For women, protective factor for asthma was cheese/brown bread (OR 0.88, 95% CI 0.82–0.94).  Age group, education, weight status, physical activity weekly minutes quartile, smoking status  8 (positive)
Shi et al31People’s Republic of China  n=1,486, cohort  Ever asthma  PCA: 4 dietary patterns (“macho”, “traditional”, “sweet tooth”, “vegetable rich”); 33-item FFQ  “Traditional” pattern (rice, fresh vegetables) was positively associated with ever asthma (OR 2.25, 95% CI 1.45–3.51).  Age, sex, smoking, income, manual job, BMI, energy, MSG intake, all other dietary pattern scores  8 (positive)
Bakolis et al20UK  599 cases and 854 controls; 16–50 years; 60% female; case-control study  (Current) asthma, quality of life  PCA: 5 dietary patterns (“prudent”, “vegetable and fruit”, “Western”, “vegetarian”, “traditional”); over 200-item FFQ  No clear relation between the dietary patterns and asthma outcomes was observed.  Age, sex, BMI, social class, housing tenure, employment status, whether a single parent, smoking, passive smoke exposure at home, total energy intake, ethnicity, number of siblings, paracetamol and supplement use, all other dietary patterns  8 (neutral)
Hooper et al23Germany, UK, Norway  n=1,174; 29–55 years; cross-sectional  Current asthma, asthma symptom score, FEV1  PCA: 2 dietary patterns (“meats and potatoes” and “fish, fruit and vegetables”); 158-, 198-, or 204-item FFQ  No association was observed between the dietary patterns and current asthma, asthma symptoms, and FEV1  Age, sex, social class, smoking status, exercise, BMI, quintiles of total energy intake, other dietary pattern  8 (positive)
McKeever et al26The Netherlands  Cross-sectional: n=12,648; 41.5±11.2 years; 52% female; cohort: n=2,911; 45.0±9.5 years; 50% female  Cross-sectional: FEV1, prevalence of asthma and wheeze; cohort: FEV1 decline  PCA: 3 dietary patterns: (“cosmopolitan”; “traditional”; “refined foods”); 178-item FFQ  “Traditional diet” (high intake of meat and potatoes and lower intake of soy and cereal) was negatively associated with FEV1 (5th versus 1st quintile −94.4 mL; 95% CI −123.4, −65.5 mL). “Cosmopolitan” was positively associated with wheeze (OR 1.3, 95% CI 1–1.5) and asthma (OR 1.4, 95% CI 1–1.9). No dietary patterns were associated with lung function decline.  Age, sex, smoking status, pack-years of smoking, education level, location  8 (positive)
Varraso et al27France  n=54, 672; asthmatics 52.5±6.5 years; nonasthmatics 52.7±6.5 years; 100% female; cohort  Current asthma, adult-onset asthma, and frequency of asthma attacks  Factor analysis: 3 dietary patterns: (“prudent”; “Western”; “nuts and wine”); 66-item FFQ  No dietary pattern was associated with asthma incidence or current asthma. Western pattern (pizza, salty pies, desserts, and cured meat) was a risk factor for asthma attacks (highest versus lowest tertile OR 1.79, 95% CI 1.11–3.73) while nuts and wine pattern was protective (highest versus lowest tertile OR 0.65, 95% CI 0.31–0.96).  Age, energy intake, BMI, smoking, physical activity, menopausal status, education, multivitamin supplement use  8 (positive)
Sexton et al21New Zealand  38 adults with symptomatic asthma; high intervention: 38.0±4.2 years, 88% female; low intervention: 37.0±4.0 years, 67% female; control: 40.2±4.0 years, 67% female; 12-week RCT  Asthma control (ACQ), asthma-related quality of life, FEV1, FVC, inflammatory markers.  Mediterranean diet; 142-item FFQ  With significantly increased Mediterranean score, the high intervention group achieved small but insignificant improvement in asthma-related quality of life and prebronchodilator FEV1 and FVC. No changes were observed in asthma control or inflammatory markers.  Age, sex  6 (neutral)
Shaheen et al24UK  n=2,942; male 65.7±2.9 years; female 66.6±2.7 years; 47% female; cross-sectional  FEV1, FVC, FEV1/FVC  PCA: 2 dietary patterns (“prudent”; “traditional”); 129-item FFQ  A “prudent” pattern was positively associated with FEV1 (men, adjusted coefficient 0.18 L, 95% CI 0.08–0.28 L; women, adjusted coefficient 0.08 L, 95% CI 0.00–0.16 L) and FVC (men, adjusted coefficient 0.03; 95% CI 0.00–0.05; women, adjusted coefficient 0.03; 95% CI 0.01–0.04) in both men and women.  Age, height, smoking status, pack-years, smoke in home, age left education, home ownership status, number of rooms, number of 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  8 (positive)
Barros et al25Finland  n=174; 40±15 years; 82% female; cross-sectional  Asthma control (controlled defined as FEV1 ≥80%, FeNO ≤35 ppb, and ACQ score <1)  Mediterranean diet; 86-item FFQ  Mediterranean diet reduced 78% (OR 0.22, 95% CI 0.05–0.85) the risk of uncontrolled asthma.  Sex, age, education, inhaled corticosteroids, energy intake  8 (positive)
Varraso et al28USA  n=72,043; 30–55 years; 100% female; cohort  Prevalence of adult-onset asthma between 1984 and 2000  PCA: 2 dietary patterns (“prudent”; “Western”); 116-item FFQ  Dietary patterns were not associated with adult-onset asthma.  Age, smoking status, pack-years, pack-years2, exposure to secondhand tobacco smoke, menopausal status, race-ethnicity, spouse’s educational attainment, physician visits, US region, BMI, physical activity, multivitamin use, energy intake  8 (positive)
Varraso et al29USA  n=42,917; 40–75 years; 100% men; cohort  Prevalence of adult-onset asthma between1986 and 1998  PCA: 2 dietary patterns (“prudent”; “Western”); 131-item FFQ  Dietary patterns were not associated with adult-onset asthma.  Age, smoking, pack-years, pack-years2, race/ethnicity, physician visits, US region, BMI, physical activity, multivitamin use, energy intake  8 (positive)
Butler et al30Singapore  n=52,325; 45–74 years; cohort  Prevalence of new-onset asthma between baseline and follow-up  PCA: 2 dietary patterns(“meat-dim sum”; “vegetable-fruit-soy”); 165-item FFQ  Dietary patterns were not associated with new-onset asthma.  Age, total energy intake, dialect group, sex, smoking status, age at starting to smoke, cigarettes per day, adult environmental tobacco smoke exposure, education, (nonstarch polysaccharide intake)  8 (positive)
Notes:
a  The first six studies were included in meta-analysis because all examined ever or current asthma as the primary outcome
b  quality was scored and rated independently using the American Dietetic Association Quality Criteria Checklist. Pack-years was defined as the number of packs smoked per day multiplied by the number of years smoked. The authors adjusted for both pack-years and the square of pack-years (pack-years2).
Abbreviations: ACQ, asthma control questionnaire; BMI, body mass index; CI, confidence interval; FFQ, food frequency questionnaire; OR, odds ratio; PCA, principal component analysis; FVC, forced vital capacity; FEV1, forced expiratory volume in one second; MSG, monosodium glutamate; RCT, randomized controlled trial.