Asthma, rhinoconjunctivitis and eczema (ARE) are a complex set of diseases whose exact causal mechanisms are yet to be uncovered. They are known to be multifactorial, with both a combination of genetic and environmental factors playing a role. A range of research pertaining to the link between some of the environmental factors involved has been carried out by the International Study of Asthma and Allergies in Children (ISAAC), particularly the effect of diet.1,2 Over the past 20 years the prevalence of these diseases has increased in many areas around the world, including New Zealand, which has one of the highest rates of asthma in the world.3 The recent increase in these diseases over the past two decades indicates that changes in environmental factors are likely to play a key role, perhaps more so than genetics. This is further supported by the vast variation in prevalence of the diseases between and within countries, suggesting that potentially avoidable causes may be present. Among these environmental factors, recent research has suggested that diet may be important in the development and severity of ARE, with certain foods such as fruit and vegetables playing a protective role, while others such as fast food acting as risk and/or exacerbating factors.2,5–21 The consumption of fast food is on the rise globally,2 and the significance of understanding the health implications of this increase in consumption is becoming increasingly critical for many chronic conditions. This study aimed to demonstrate a suitable methodology for investigating a possible correlation between fast food consumption and the prevalence and severity of ARE in school children, using distribution and density of fast food restaurants in the same centres that participated in the ISAAC studies (listed in Appendix A) as a surrogate measure for fast food consumption.

No large scale study using multiple fast food chains has been conducted comparing the distribution of fast food outlets and ARE prevalence. A study in 1998 using ISAAC data was conducted using McDonalds restaurants per 100,000 population in each country, as a surrogate measure for diet, and compared this to the prevalence of current wheeze in 13–14-year-old children, and found a significant correlation after accounting for Gross National Product as a confounder.20 Another study used ISAAC data and food frequency questionnaires and found that frequent consumption of hamburgers showed a dose-dependent association with asthma symptoms, and frequent takeaway consumption showed a similar association with bronchial hyper-responsiveness.16

A major epidemiological study investigating fast food and ARE was conducted using ISAAC Phase Three data and found that an increased risk of ARE in adolescents and children was correlated with high consumption of fast food (>3 times per week).2 Although the study showed promising results that a correlation between fast food and ARE (particularly severe asthma) exists, more work is required to establish a causal relationship. The current study has identified a new methodology to investigate this area.

Fast foods lack many of the nutrients found in fruits and vegetables and are high in omega-6 PUFAs (trans-fats), sodium, and added sugars.4 Hypotheses regarding the effect of the diet on asthma relate to both antioxidants and immunomodulatory mechanisms.7,10,14 The complex aetiology of allergic disease has led to a variety of theories regarding the impact of diet on ARE, such as fat and salt consumption leading to hypersensitisation of the airway.8,22 Links between consumption of fast food, or high intake of dietary components commonly found in fast food (such as trans-fats, saturated fat, sugar and salt) and symptoms of ARE have been shown by various studies.8,11,22–27 Symptoms of asthma have also been attributed to high sugar intake, particularly in children. A high sucrose diet has been thought to impair the pulmonary innate immune system and increase susceptibility to airway inflammation.24

As McDonald's and Burger King were the only two fast food restaurants which were in common across all seven countries that were surveyed, the study was restricted to the use of these two restaurant chains in the analysis. A number of centres were excluded from the analysis due to inaccurate population values either due to a reporting error or not all schools in the area being included in the sampling frame. The results from the analysis are summarised in Fig. 1(A–F).

Figure 1.

Trends of prevalence of current and severe asthma, rhinoconjunctivitis and eczema in relation to outlet density.

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The ‘Current’ category (A, C and E) for each of the three diseases included all adolescents who exhibited symptoms in the past 12 months of that particular disease. The ‘Severe’ category for asthma (B) used the percentage of Adolescents with wheeze in the past 12 months who also exhibited severe symptoms such as sleep disturbance, wheeze affecting speech, four or more acute attacks, exercise wheeze and night cough. ‘Severe’ rhinoconjunctivitis (D) was a combination of current nose symptoms, current nose symptoms and itchy-watery eyes and the answer “A lot” to having this nose problem interfere with daily activities. ‘Severe’ eczema (F) used a combination of those with current symptoms and those with sleep disturbance one or more nights per week.

All linear regressions showed a positive trend except for A, which showed a negative trend. The most significant of these was the relationship between current eczema and outlet density (E).

This project has shown that it is practical to systematically obtain and map fast food outlets and compare their distribution worldwide with the prevalence and severity of diseases, in this case ARE. However, none of the analyses showed statistical significance, which may be due to the small sample size, or may mean that a correlation does not actually exist.

The devised methodology has proven to be an efficient way to obtain and map large amounts of restaurant distribution data in a form that is manageable and suitable for additional analysis such as to compare with area-based disease prevalence. Thus the project has proven to be feasible and successful in indicating a larger scale investigation. A future study should include a systematic and documented process to obtain restaurant data for all possible countries included in ISAAC Phase Three, and perhaps a more thorough investigation of fast food outlets in each country, as the types of fast food available differ greatly from country to country. It may be valuable to compare an analysis using only common restaurants and an analysis using all available restaurants, and observing whether results differ. In this study, after exclusions were applied, 6 of the 53 centres (11%) had neither a McDonald's nor a Burger King restaurant within the region, and therefore had an outlet density of 0. These areas may well have had a number of local chains of similar fast food type restaurants which have not been accounted for in this study, which may bias the data. However, obtaining outlet distribution data for small, local chains would not only be time consuming and challenging, but may introduce a bias of its own if data for local chains were more easily obtainable for some areas rather than others. This study also only looked at ISAAC data for 13–14 year olds, as this was available for a higher proportion of the investigated centres, but a future study with a larger sample of centres should also utilise the ISAAC data for 6–7 year olds. It may also be of use to compare analyses between the two age groups as there are likely to be differences in the consumption of fast food between these two age groups.

In terms of validity, there are a number of measures that would need to be addressed in future studies to ensure minimisation of bias in the results. Correlations found in this study may in part be a result of lifestyle, other environmental cofactors, culture, or economy. Adjustment of potential confounders is an important part of the analysis and ISAAC has individual data of numerous covariates such as television watching, maternal smoking, maternal education, language, exercise and GNI. Ecological studies tend to be susceptible to confounding in general, and in this particular case, as we are dealing with the multifactorial diseases of asthma, rhinoconjunctivitis and eczema accounting for confounding is especially important. Other potential confounders to adjust for may include socioeconomic position and obesity (BMI). The nature of this study (the timescale for a summer studentship) did impose limitations on the ability to accurately gauge and adjust for confounders, particularly when dealing with differences within individual centres. ISAAC centres are geographical areas which vary vastly in size, ranging from small rural towns to large, diverse cities. For example, the Auckland region is accounted for as a single ISAAC centre, but has a wide range of difference within it for variables such as socioeconomic position, which makes accounting for some confounders challenging. For this methodology the confounders would need to be converted from individual-based measures to area-based means (or medians), which was not practical for this study given the timescale, but would definitely be achievable for a future study. In addition, the inclusion of more low and middle income countries would strengthen the results.

It is interesting to note that the only variable in this study which seemed to show a clearly observable positive association was between outlet density and current eczema, more so than for severe categories of any of the diseases. This is in contrast with the ISAAC study2 using individual data, which found greatest correlation with severity of ARE and the consumption of fast food, rather than prevalence, however the number of centres and numbers of participants in the ISAAC diet analysis was far greater than those used in this study and would have had more power to detect associations. The inference that fast food may worsen the severity of ARE in individuals with one of the diseases, rather than affecting the prevalence of said disease, is only supported for asthma in this study.

As the significance of all results is quite low and the sample size quite limited, all the above inferences are made with caution. The main aim of this project, for a summer studentship, was to determine the feasibility of the methodology of investigating fast food and ARE in this way, and this project has achieved that aim. With the growing fast food industry and increasing consumption of fast food in New Zealand and internationally, and with an increasing burden of non-communicable diseases, the significance of understanding the health implications of these changes is becoming increasingly relevant for healthcare both at a population health level and for individual care. The methods devised from this project for obtaining and analysing the distribution of fast food outlets may be useful in future for determining relationships between diet and disease. The methodology used is not necessarily restricted in scope to asthma, rhinoconjunctivitis and eczema as used in this project, and may be applied to a more expansive list of diseases potentially related to nutrition. Information from future studies using this methodology may be highly relevant to the health sector in terms of highlighting the need for a healthy diet, and providing reasons to decrease consumption of fast food, especially for those children and adults affected by chronic diseases.

The studentship was funded by the University of Auckland Faculty of Medical and Health Sciences, which had no role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.

None.