# Diet and Asthma: A Narrative Review
## 4 Diet and Asthma
### Fats and Fish
Another study observed that a single high-fat/high-energy meal increases neutrophil airway inflammation and TLR4 mRNA expression in sputum cells and decreases bronchodilator responsiveness in patients with asthma [77]. However, the high-fat meals had a diverse nutritional profile, which included fats of various qualities as well as other macronutrients, which may have had an impact on the inflammatory response [77]. No changes in eNO levels were observed after the high-fat meal. However, as stated before, eNO is a marker of eosinophil asthma, and as the inflammatory changes observed were increases in airway neutrophils, it is not surprising that eNO levels were left unaltered [77]. In the same study, another group of patients with asthma consumed a high-trans (\(n\) = 5; 5.2 g trans-fat) or non-trans (\(n\) = 5, \(<\)0.3 g trans-fat) fatty acid meal. After the high-trans fatty acid meal, sputum % neutrophils were found to be significantly higher than after the non-trans meal [77]. Higher ingestion of saturated fatty acid-rich foods, such as butter, appears to be associated with both a higher asthma symptom score and a higher degree of airway inflammation [55]. On the other side, the consumption of olive oil (a monosaturated rich type of fat) in a multi-case study of Italian adults, showed that intakes of oleic acid and of olive oil were associated with a reduced risk of current asthma. Individuals in the highest quartile of oleic acid intake had less than half the chance of having current asthma in comparison to those in the lowest quartile. Moreover, these authors uncovered that when considering olive oil intake as a continuous variable, the risk of having current asthma declined by 20% for an increase of 10 g/day in olive oil consumption [80]. Olive oil is also rich in phenolic compounds and may exert its protective effects through additional anti-inflammatory and antioxidants effects [80]. The consumption of fish (the principal source of \(n\)-3 PUFA) was found to be inversely associated to asthma in the previously referred study of 598 Dutch children [68], with the adjusted OR for current asthma being 0.34 (95% CI 0.13; 0.85) and for atopic asthma with bronchial hyperresponsiveness, 0.12 (95% CI 0.02; 0.66), respectively [68]. In another study, school children who consumed fish more often had less doctor-diagnosed asthma and less current asthma [81]. However, evidence of fish oil and fish benefits in asthmatic patients are inconsistent [82]. An inverse association between consumption and asthma risk seems to be more evident in children, as their immune system is still under development: a meta-analysis found that infant fish consumption was inversely related to the occurrence of asthma in childhood. When comparing the highest to lowest category of fish consumption, the pooled RR of asthma was 0.76 (95% CI, 0.61; 0.94) [82]. Two different studies from the previously referred meta-analysis examined the relationship between maternal fish consumption during pregnancy and the risk of asthma in offspring. However, as the exposures assessed in these studies were different, they did not combine their results through meta-analysis. In one of the studies, there was no significant association found between maternal fish consumption frequency during pregnancy and the development of asthma in offspring (OR = 1.01, 95% CI 0.85; 1.20) when comparing mothers who consumed fish more than once a week with those who consumed fish less than once a week. Similarly, the other included study reported that maternal plasma long-chain \(n\)-3 polyunsaturated fatty acid (LCn3 PUFA) concentration was not associated with the risk of asthma in offspring [82]. However, the levels of LCn3 PUFAin maternal expressed breast milk (EBM) were found to have a negative association with the occurrence of asthma in offspring. When comparing the group with the highest levels of LCn3 PUFA to the group with the lowest levels, there was a combined RR = 0.71 (95% CI, 0.52-0.96).