New research presented at this year's meeting of the Thoracic Society of Australia and New Zealand (TSANZ) suggests the increasing prevalence of poor quality diets containing high volumes of processed food, fat and refined sugar could be increasing inflammation in the body and contributing to increased asthma prevalence. The research is by Associate Professor Lisa Wood, Head of the Nutrition programme at the Centre for Asthma and Respiratory Diseases, University of Newcastle, NSW, Australia, and colleagues.
In 2009 the Dietary Inflammatory Index (DII) was developed by colleagues at the University of South Carolina, USA, and validated to assess the inﬂammatory potential of individual diets. In this new study, Wood and colleagues examined the DII in subjects with asthma compared to healthy controls, in order to relate the DII to asthma risk, lung function and systemic inﬂammation. They studied 99 people with stable asthma and 61 healthy controls, all based in Newcastle/NSW, and recruited from previous study databases, advertisements encouraging people to take part, and outpatient clinics. Participants underwent blood tests and spirometry was performed to test their lung function. The DII was calculated from food frequency questionnaires administered to study subjects.
The team also found that lung function was significantly associated with DII score, with lung function being reduced by around 10% in the third of patients with the highest DII score versus the third of patients with the lowest. Another indicator of inflammation"levels of the inflammatory marker interleukin-6 in the blood"was also positively associated with DII score.
The team also found that lung function was significantly associated with DII score, with lung function being reduced by ~10% in the third of patients with the highest versus DII score the third of patients with the lowest. Another indicator of inflammation"levels of the inflammatory marker interleukin-6 in the blood"was also positively associated with DII score.
Associate Professor Wood says: 'The usual diet consumed by asthmatics in this study was pro-inﬂammatory relative to the diet consumed by the healthy controls, as assessed using the DII score. The DII score was associated with lower lung function and increased systemic inﬂammation. Hence, consumption of pro-inﬂammatory foods in the diet may contribute to worse asthma status."
Wood and her team are now designing additional studies examining how dietary components, as described by the DII, modulate inflammation and clinical asthma outcomes. The potential role of saturated fat as an inflammatory agent, and dietary fibre and antioxidants as anti-inflammatory agents, are being examined.
In another study, Wood, along with Dr Mehra Haghi and colleagues at the University of Sydney, studied the effects of dietary fat on the effectiveness of ventolin, the most common inhaler-based treatment for asthma. A/Prof Wood had already demonstrated a high fat meal consisting of a mixture of saturated fatty acids (SFAs) and polyunsaturated fatty acids (PUFAs) had reduced patient responses to ventolin (also known as salbutamol). 'One potential mechanism by which FAs may interfere with bronchodilation involves inhibition of drug transport across the airway epithelium," says Dr Wood.
In this new study, the researchers investigated the impact of FAs (palmitic acid, a SFA, and arachidonic acid and eicosapentanoic acid, both PUFAs). The researchers analysed the effect of exposure to these FAs on salbutamol transport through bronchial epithelial cells. The cells were developed using a fat-free medium and were used for transport study after 12 days. Following this, the cells were incubated for one hour with 30 μM of each FA. Salbutamol was then added, and after 4 hours the change (if any) in concentration of salbutamol was analysed.
'We found that the amount of salbutamol transported through cell membrane was significantly higher in the presence of PUFAs compared with SFAs or no fats at all," says Dr Haghi. 'Incubation with PUFAs appeared to reduce the stiffness of the cell membrane. Our findings suggest that the presence of PUFAs is essential for membrane ﬂuidity. Our findings also demonstrate that if saturated fatty acids are present, then this effect is lost and drug transport is inhibited."
She concludes: 'The study provides the ﬁrst evidence that the transport of salbutamol can be modiﬁed by varying dietary fat consumption.While polyunsaturated fatty acids enhance drug transport, the presence of saturated fat inhibits drug transport, which is likely to interfere with relaxation of the airways."