New research published in Thorax examines the association between higher cured meat intake and worsening asthma symptoms over time, using BMI as a mediator.
Dr Bright Nwaru from Asthma UK Centre for Applied Research at the University of Edinburgh, said:
“The study by Li and colleagues showing that consumption of cured meat may lead to worsening asthma symptoms in adults adds to the literature on the role of diet in asthma. Whilst the results are interesting, the risk estimates were overall only moderate. Many participants dropped out of the study overtime and some key factors (e.g. socioeconomic status, stress, indoor air pollution) were not also considered in the study. Importantly, this topic is still at its very early stage, hence the need for more studies before the picture is clear.”
Catherine Collins RD FBDA, Spokesperson for The British Dietetic Association, said:
“Nitrites are an interesting group of substances found in foods. They’re used as a preservative for ‘cured’ meats like ham and sausages (E249 / E250). But they’re also made by our mouth bacteria after we’ve consumed nitrate-rich foods and drinks such as beetroot and green leafy vegetables, or processed foods containing nitrate preservatives E251 and E252.
“Dietary nitrate is absorbed into our bloodstream, secreted into saliva, and converted by mouth bacteria into nitrites. Once swallowed these newly formed nitrites undergo the same metabolic fate as nitrites from food sources. Blood nitrate and nitrite levels can be measured as a proxy marker of dietary intake.
“So this research on asthma and processed meats is interesting, given earlier work from the same group failed to show any association between processed meat consumption and blood levels of nitrites and nitrates, but did suggest a link between blood levels from green leafy vegetable intake and pollution1. This paper focuses on processed meats alone, and excludes the confounding variable of green leafy vegetable consumption.
“There are two key areas of concern with the dietary information provided.
“At first glance the study shows an increase in calories, total and saturated fat and salt intake as processed meat consumption increased, which would be expected as some processed meats (such as salami, liver sausage, sausages) are rich in these. But closer inspection shows the increase isn’t proportional across increasing intakes, suggesting other foods rich in fat and saturated fats are contributing to dietary intake overall. I’d suggest this reflects variable intakes of dairy foods across this group which isn’t included in this analysis.
“Secondly, the asthma group with the highest intakes of processed meats also have the highest calorie intakes and the highest proportion (12% sample) of obese individuals. This is important as obesity is linked to asthma2. Yet 40% of this group had a ‘lean’ BMI (below 22.5), which can’t be accounted for by adjustments for age, activity, disease severity or smoking history. As a Registered Dietician I’m not convinced the questionnaire used was sufficiently detailed to allow dietary recommendations to be made.
“Diet does have a role to play in prevention and management of asthma, but an association with one aspect of diet – in this case processed meats – doesn’t, and can’t, imply causation. A varied and Mediterranean-style diet remains the optimal anti-inflammatory style diet, whether you have asthma or not.”
Leafy vegetable consumption in this 2012 paper was defined as the sum of the intake for salad, raw or cooked endives, raw or cooked watercress, or cooked spinach, foods typical in French diets.
Cured meat (serving/day) all subjects 0.14 (0.07, 0.21); asthmatics 0.14 (0.07, 0.21); non-asthmatics 0.14 (0.07, 0.28) p<.001
Nitrite/nitrate concentration, Median (Q1–Q3) In plasma (lM) all subjects 36.3 (25.7, 51.1) ; asthmatics 35.5 (24.2, 51.2); non-asthmatics 37.0 (26.8, 51.1) p 0.42
* ‘Cured meat intake is associated with worsening asthma symptoms’ by Zhen Li et al. published in Thorax at 23.30 UK time on Tuesday 20 December 2016.