EDITORIAL

Breathing what we eat

Key words: asthma, diet, obesity.

The world is in the midst of an unprecedentedobesity epidemic.1 In fact, among adults in theUnited States, recent studies find only a minority ofadults are now in the ‘normal’ weight category.2 Withthis epidemic has come the realization that obesity isa major risk factor for asthma and is associated withsevere and poorly controlled asthma.3 The reasonsfor this are likely to be multifactorial, but one factorthat must be considered is the significant changes indiet that have taken place in recent decades. Thechanges in diet not only cause obesity, but are likelyto be important in the pathogenesis of airwaydisease. The study by Berthon et al.4 in this issue ofthe journal highlights the need for further investiga-tion in this area.

There has been a major shift in the type of dietconsumed by individuals living particularly in devel-oped countries. Diets are now higher in fat, salt andsugar, and lower in fibre and anti-oxidants. Certainly,this predisposes to the type of weight gain that leadsto obesity, but this type of diet does more than packon the weight. There is an emerging literatureshowing how this type of diet leads to increased pro-duction of inflammatory mediators and reactiveoxidant species.5 A high-fat, high-carbohydrate mealincreases reactive oxidant species production fromcirculating mononuclear cells and polymorphonu-clear leucocytes and also increases nuclear transloca-tion of the pro-inflammatory transcription factornuclear factor kB.6 Conversely a high-fat, high-fibrediet of equal calories does not induce these samemarkers of inflammation.7 It is not just a question ofhow much you eat; what you eat produces majorchanges in markers of metabolic stress and can leadto long-term cardiovascular and metabolic disease.This is now well accepted, and studies suggest thatdiets, such as the Mediterranean diet, produce signifi-cant benefits on cardiovascular outcomes and all-cause mortality.8

We are just beginning to appreciate the effect thatdiet may be having on asthma. There has been a greatdeal of attention focused on the potential role of dietand even maternal diet in the development of child-hood allergic asthma,9 and a number of studies havelooked at supplementation with various elements andanti-oxidants to see if any of these can improveasthma outcomes in those with established asthma.

However, the results of many of these small studieshave been inconclusive.10

The recent publication by Berthon et al. provides animportant perspective on diet and asthma, and pointsto a way forward for future investigations.4 In thiscross-sectional study of healthy controls and asthmat-ics of varying severity, severe persistent asthmaticswere found to consume more fat and sodium, withless fibre and potassium, although overall energyintake was similar. Among asthmatics, high fat wasassociated with increased airway eosinophilic inflam-mation and a trend towards increased airway neu-trophilic inflammation. Low fibre was associated withlow lung function and lower airway eosinophilia. Theauthors present a number of plausible links betweenfibre and fat intake and airway inflammation inasthma. As a cross-sectional study, it is not possible toshow causation, but these findings add significantly toan emerging literature on this topic. In a prospectivestudy, the same group found that an acute challengewith a high-fat diet increased airway neutrophilia anddecreased bronchodilator responsiveness.11

Observational12 and small interventional studies13

suggest that Mediterranean-type diets and diets highin fish and fibre14 may have beneficial effects onasthma symptoms, lung function and even preva-lence of asthma in adults.

Significant changes in dietary composition appearto produce significant changes in airway inflamma-tion and asthma control.

These are very important observation, suggestingthat interventional studies of diet in asthma will be ofthe utmost importance and that dietary compositionmay be an important factor contributing to poorasthma control. There are a number of studies cur-rently underway that have focused on specificvitamin deficiencies or supplementation with anti-oxidants.15 While these types of studies are obviouslyof scientific interest, in that they help determinewhich particular factor in a diet is likely to be causingdisease, the fact is that the Western diet does notreflect a single change in one nutrient but has been acomplicated natural experiment based on a multifac-eted dietary change. It is likely that future interven-tional studies should focus on transforming the dietaway from the typical Western diet, to one that islower in fats, salts and sugar, and higher in fibre andanti-oxidants. Such studies are going to be crucial aswe struggle to treat patients with severe uncontrolledasthma in the 21st century.

Anne E. Dixon, MA, BM, BChUniversity of Vermont, Burlington, Vermont, USA

Supported by NIH grants: P20 RR15557, RR019965, P30 GM103532.

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© 2013 The AuthorRespirology © 2013 Asian Pacific Society of Respirology

Respirology (2013) 18, 391–392doi: 10.1111/resp.12056

REFERENCES

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2 Mastronarde JG, Anthonisen NR, Castro M et al. Efficacy ofesomeprazole for treatment of poorly controlled asthma. N. Engl.J. Med. 2009; 360: 1487–99.

3 Dixon AE, Holguin F, Sood A et al. An official American ThoracicSociety Workshop report: obesity and asthma. Proc. Am. Thorac.Soc. 2010; 7: 325–35.

4 Berthon BS, Macdonald-Wicks LK, Gibson PG et al. An investi-gation of the association between dietary intake, disease severityand airway inflammation in asthma. Respirology 2013; 18:447–54.

5 Dandona P, Ghanim H, Chaudhuri A et al. Macronutrient intakeinduces oxidative and inflammatory stress: potential relevanceto atherosclerosis and insulin resistance. Exp. Mol. Med. 2010; 42:245–53.

6 Aljada A, Mohanty P, Ghanim H et al. Increase in intranuclearnuclear factor kappaB and decrease in inhibitor kappaB inmononuclear cells after a mixed meal: evidence for a proinflam-matory effect. Am. J. Clin. Nutr. 2004; 79: 682–90.

7 Ghanim H, Abuaysheh S, Sia CL et al. Increase in plasma endo-toxin concentrations and the expression of Toll-like receptorsand suppressor of cytokine signaling-3 in mononuclear cells

after a high-fat, high-carbohydrate meal: implications for insulinresistance. Diabetes Care 2009; 32: 2281–7.

8 Mitrou PN, Kipnis V, Thiebaut AC et al. Mediterranean dietarypattern and prediction of all-cause mortality in a US population:results from the NIH-AARP Diet and Health Study. Arch. Intern.Med. 2007; 167: 2461–8.

9 Misak Z. Infant nutrition and allergy. Proc. Nutr. Soc. 2011; 70:465–71.

10 Kim JH, Ellwood PE, Asher MI. Diet and asthma: looking back,moving forward. Respir. Res. 2009; 10: 49.

11 Wood LG, Garg ML, Gibson PG. A high-fat challenge increasesairway inflammation and impairs bronchodilator recovery inasthma. J. Allergy Clin. Immunol. 2011; 127: 1133–40.

12 Romieu I, Barraza-Villarreal A, Escamilla-Nunez C et al. Dietaryintake, lung function and airway inflammation in Mexico Cityschool children exposed to air pollutants. Respir. Res. 2009; 10:122.

13 Sexton P, Black P, Metcalf P et al. Influence of Mediterraneandiet on asthma symptoms, lung function, and systemic inflam-mation: a randomized controlled trial. J. Asthma 2013; 50: 75–81.

14 Uddenfeldt M, Janson C, Lampa E et al. High BMI is related tohigher incidence of asthma, while a fish and fruit diet is related toa lower—results from a long-term follow-up study of three agegroups in Sweden. Respir. Med. 2010; 104: 972–80.

15 Allan K, Devereux G. Diet and asthma: nutrition implicationsfrom prevention to treatment. J. Am. Diet. Assoc. 2011; 111:258–68.

Editorial392

© 2013 The AuthorRespirology © 2013 Asian Pacific Society of Respirology

Respirology (2013) 18, 391–392