Associations between asthma and the nutritional quality of diet remain poorly understood. We investigated the associations between overall quality of diet evaluated by three dietary scores (the Alternate Healthy Eating Index 2010 (AHEI-2010), the literature-based adherence score to Mediterranean diet (MEDI-LITE) and the modified Programme National Nutrition Sante Guideline Score (mPNNS-GS)) and the asthma symptom score and asthma control. In 2017, 34 766 participants from the NutriNet-Sante cohort answered a detailed respiratory questionnaire. Asthma was defined by the asthma symptom score (as the sum of five questions) and asthma control by the asthma control test (ACT). Roughly 25% of participants reported at least one asthma symptom and for the three dietary scores we observed a statistically significant negative association between a healthier diet and the asthma symptom score (for AHEI-2010, the adjusted OR was 0.79 (95% CI 0.75-0.84) for women and 0.67 (95% CI 0.60-0.75) for men). Among participants with asthma (n=2609) we also observed a negative association between a healthier diet and poorly controlled asthma. This was significant in men (OR 0.39 (95% CI 0.18-0.84) for the AHEI-2010) and borderline significant in women (OR 0.73 (95% CI 0.53-1.01) for the AHEI-2010; p=0.06 for trend). Healthier diet behaviours were associated with fewer asthma symptoms and greater asthma control.