Pilot randomised trial of a healthy eating behavioural intervention in uncontrolled asthma

Abstract

Rigorous research on the benefit of healthy eating patterns for asthma control is lacking.We randomised 90 adults with objectively confirmed uncontrolled asthma and a low-quality diet (Dietary Approaches to Stop Hypertension (DASH) scores <6 out of 9) to a 6-month DASH behavioural intervention (n=46) or usual-care control (n=44). Intention-to-treat analyses used repeated-measures mixed models.Participants were middle-aged, 67% female and multiethnic. Compared with controls, intervention participants improved on DASH scores (mean change (95% CI) 0.6 (0, 1.1) versus -0.3 (-0.8, 0.2); difference 0.8 (0.2, 1.5)) and the primary outcome, Asthma Control Questionnaire scores (-0.2 (-0.5, 0) versus 0 (-0.3, 0.3); difference -0.2 (-0.5, 0.1)) at 6 months. The mean group differences in changes in Mini Asthma Quality of Life Questionnaire overall and subdomain scores consistently favoured the intervention over the control group: overall 0.4 (95% CI 0, 0.8), symptoms 0.5 (0, 0.9), environment 0.4 (-0.1, 1.0), emotions 0.4 (-0.2, 0.9) and activities 0.3 (0, 0.7). These differences were modest, but potentially clinical significant.The DASH behavioural intervention improved diet quality with promising clinical benefits for better asthma control and functional status among adults with uncontrolled asthma. A full-scale efficacy trial is warranted.

FIGURE 1

CONSORT chart. ACQ: Asthma Control Questionnaire. ^#: ACQ score was computed as the mean of the complete seven-item scores (ACQ7) or the six-item scores (ACQ6) if forced expiratory volume in 1 s was missing because spirometry was not performed or not usable per American Thoracic Society standards.

FIGURE 2

Fitted distributions and sorted values of changes in a, b) Dietary Approaches to Stop Hypertension (DASH) and c, d) Asthma Control Questionnaire (ACQ) scores at 6 months. ^#: DASH scores were calculated based on combining nine nutrient targets (i.e. total fat, saturated fat, protein, cholesterol, fibre, magnesium, calcium, sodium and potassium). The intermediate target of each nutrient was half-way between the DASH target and population mean (based on the National Health and Nutrition Examination Surveys 2007–2008, latest data available at the inception of this study). For a nutrient, participants reaching the DASH target were assigned 1 point, those reaching the intermediate target were assigned 0.5 points and those not meeting the intermediate target were given 0 points. The DASH score was the sum of points for all nine nutrients [12].

FIGURE 3

a) Baseline DASH, ACQ and MiniAQLQ scores, and their net-of-control improvements at 6 months. b) Percentage of participants meeting minimal clinically significant improvement (⩾0.5) in ACQ and MiniAQLQ at 6 months. DASH: Dietary Approaches to Stop Hypertension; ACQ: Asthma Control Questionnaire; MiniAQLQ: Mini Asthma-specific Quality of Life Questionnaire. ^#: mean±SD; ^¶: covariate-adjusted, mixed-model-based mean (95% CI); ⁺: calculated as unadjusted between-group mean difference in change from baseline to 6 months divided by pooled standard deviation.

FIGURE 4

Log-transformed odds ratios of intervention participants relative to controls meeting minimum Dietary Approaches to Stop Hypertension intervention goals at 6 months. Bars indicate 95% confidence interval.