# Diet and Asthma: A Narrative Review
## 4 Diet and Asthma
### Fats and Fish  
Dietary fat may modulate inflammatory responses through a variety of mechanisms [48; 75; 3]. Depending on the type and source of fat consumed, it may have positive [76] or negative [77] effects on asthma. On the negative side, a high-fat diet may change the composition of the gut microbiota by altering the expansion and colonization of invasive bacteria, with a decrease in protective bacteria, and a decrease in SCFA concentration [3]. Saturated fatty acids can activate innate immune receptors including toll-like receptors (TLR)-4, resulting in altered transcription factor activity such as NF-kB, consequently stimulating the inflammatory cascade [3]. In addition, omega-6 (_n_-6) polyunsaturated fatty acids (PUFA) are also associated with pro-inflammatory responses, and are found specially in vegetable oils [78], which are typically linked with the western diet [3]. On the other side, omega-3 (_n_-3) PUFAs, namely eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), that are found in oily fish and fish oil supplements [76], were found to be beneficial in animal models of asthma [76]. EPA and DHA lipid mediators have shown to possess anti-inflammatory and inflammation-resolving properties, such as limiting neutrophil infiltration or inhibiting pro-inflammatory cytokine production [78]. Furthermore, EPA and DHA appears to directly inhibit the production of pro-inflammatory cytokines by inhibiting the activation of the nuclear transcription factor NF-kB [78]. An imbalance in _n_-6 PUFA intake versus _n_-3 PUFA intake has been proposed as a contributing \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \multicolumn{2}{p{113.8 pt}}{**Nuts**} & & & \\ \hline
**Author, Year, Study Design** & **Sample, Age** & **Dietary Assessment/Intervention** & **Results** \\ \hline [PERSON] et al., 2007, Cross-sectional [72] & A total of 690 children aged 7 to 18 years, mean age: N/R. & Dietary intake was assessed through a 58-item FFQ, including nuts consumption. & High consumption of nuts: (+) wheezing prevalence. \\ \hline [PERSON] et al., 2015, Randomized trial [73] & In total, 640 infants with severe eczema, egg allergy, or both. Mean age: 7.8 \(\pm\) 1.7 months. & Participants were stratified into two study cohorts based on the results of a skin-prick test for peanut allergy and were then randomly assigned to a group in which dietary peanuts would be consumed, or to a group in which its consumption would be avoided. & Participation were stratified into two study cohorts based on the results of a skin-prick test for peanut allergy and were then randomly assigned to a group in which dietary peanuts would be consumed, or to a group in which its consumption would be avoided. &
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline [PERSON] et al., 2014, Cohort study [74] & A total of 856 children (from 3–12 months to 6 years old) & Assessment of introduction of nuts in the first year of life. & Introduction of nuts in first year of life: (=) asthma at 6 y. \\ \hline \end{tabular}
\end{table} 
Table 3: Studies evaluating effects of nuts intake on asthma and asthma-related outcomes. factor to the rise in allergic diseases, that could be a consequence of \(n\)-6 PUFA's pro-inflammatory activity, which promotes a type 2 helper T lymphocyte immune response [78]. Concordantly, a cross-sectional study of adult asthma patients revealed a positive association between a high \(n\)-6:\(n\)-3 PUFA ratio with higher eNO values (\(\beta\) = 0.05, 95% CI 0.02; 0.09) and increased odds for uncontrolled asthma (OR = 3.69, 95% CI 1.37; 9.94) [79]. A study of subjects with severe persistent asthma found that, comparatively to healthy controls, they consumed more fat and less fiber, and these intakes were associated with lower forced expiratory volume in 1 s (FEV1) and airway eosinophil in asthmatics [48]. It was also observed that saturated fat intake was positively associated with sputum % eosinophils [48].