The burden of asthma is high

Approximately 300 million people worldwide suffer from asthma¹. The clinical course of the disease includes acute exacerbations, during which a person with asthma will experience a worsening of symptoms and reduced lung function, associated with an increase in airway inflammation. Medical practice guidelines for asthma stipulate that a key aim of treatment is to prevent exacerbations, as they pose the greatest risk to patients, cause most anxiety to patients and their families, cause the greatest stress to health care providers and generate the greatest cost to the health care system². Inhaled glucocorticoids are most commonly used to maintain asthma control and reduce exacerbation risk. However, considering the costs, side effects and non-compliance issues associated with corticosteroid use, non-pharmacological interventions to prevent exacerbations are needed to reduce the burden of disease attributable to asthma.

Fruit and vegetable intake is linked to lung health:

It has long been recognised that fruit and vegetables are an important component of a healthy diet, as they are low in energy, yet dense in nutrients such as vitamins and minerals, fibre and phytochemicals (eg polyphenols, carotenoids, indoles, isothiocyanates and organosulfur compounds). Epidemiological studies show that fruit and vegetable intake is related to improved asthma outcomes. For example, fruit intake has been inversely related to wheeze³ and chronic lung disease onset⁴ and positively associated with lung function^5,6. Tomato-based products, have been inversely associated with asthma onset⁷ and vegetables/vegetable products have been inversely associated with wheeze^8,9 and asthma onset10. These epidemiological observations have been extended by conducting two clinical intervention trials in asthma, in which the fruit and vegetable intake was manipulated.

Manipulating fruit and vegetable consumption in asthma:

In the first study, 22 subjects with asthma were required to withdraw fruit and vegetables from their diet for 10 days. They were able to consume no more than two serves of vegetables and one serve of fruit per day and were also asked to avoid consuming a list of antioxidant-rich foods, such as tea, nuts and red wine. At the end of the 10 day period, airway infl ammation had worsened and clinical outcomes, including lung function and asthma control, had worsened¹¹. In the second, longer term study, the effect of a high versus low fruit and vegetable diet in asthmatics was compared. For 14 weeks, 139 asthmatics were randomised to either a high fruit and vegetable diet (more than five serves of vegetables and two serves of fruit per day) or a low fruit and vegetable diet (less than two serves of vegetables and one serve of fruit per day).

Adopting these diets led to changes in nutrient intake, with subjects on the low fruit and vegetable diet having lower intakes of fi bre, vitamin C and carotenoids. As a result, subjects on the low fruit and vegetable diet were 2.26 times more likely to have an asthma exacerbation than subjects on the high fruit and vegetable diet. At the end of the trial, these subjects had increased systemic and airway inflammation.

In summary:

These studies have shown that manipulating fruit and vegetable intake modifies asthma symptoms, lung function and exacerbation risk. The ‘high’ and ‘low’ fruit and vegetable diets that were used in the study are very relevant to western populations. The high fruit and vegetable diet is equivalent to the dietary recommendation in both Australia¹² and the USA¹³. Conversely, the low fruit and vegetable diet represents the median usual intake for Australian adults¹⁴. Hence, these studies demonstrate the potential for typical western dietary patterns to contribute to a worsening of asthma. The conclusion is that consumption of a high fruit and vegetable diet may be helpful in the management of asthma.