The word “linked” might be a read a bit too strongly in this headline.
Data from more than 500,000 children in more than 50 countries suggests poor diet may be to blame for rising levels of these allergy-related conditions.
Fast food often contains high levels of saturated- and trans-fatty acids, which are known to affect immunity, while fruit is rich in antioxidants and other beneficial compounds, say the researchers.
In the study, children in their early teens who ate three or more weekly servings of fast food had a 39% increased risk of severe asthma.
The study authors, Prof Innes Asher, from the University of Auckland in New Zealand, and Prof Hywel Williams, from the University of Nottingham in the UK, said: “If the associations between fast foods and the symptom prevalence of asthma, rhinoconjunctivitis and eczema is causal, then the findings have major public health significance owing to the rising consumption of fast foods globally.”
Here is the link to the paper. The conclusions say this:
Conclusions If the association between fast foods and the symptom prevalence of asthma, rhinoconjunctivitis and eczema is causal, then the findings have major public health significance owing to the rising consumption of fast foods globally.
So, they found an associated between A and B. Not a causal relationship. This type of mistake is probably THE most common error when the media reports on such a study. Sometimes even the institution that did the study puts too much emphasis on “cause” when the study didn’t establish cause at all. These types of studies CAN NOT determine cause. It was not an experiment. It was a survey. Answers were given via questionnaires, thus subjective – as in what did you eat, how is your condition today? An experiment must be designed to be far more rigorous to eliminate all other variables and narrow in on a cause. In this case, there is an association (which the piece actually notes) which means they are seen together. We don’t know how they are associated or if this is dependent on another factor such as social or economic variables.
This is why you need to be VERY doubtful about headlines and never assume a causal relationship unless the study is a very controlled experiment.
Tip: Agent J
Thanks to @thePapersBehind