"Eating a deep-fried Mars bar could give you a stroke in minutes," reports the Metro.
However, the study that prompted this headline found no evidence that the Scottish snack can potentially trigger a fatal stroke within minutes.
The over-alarmist headlines are based on the results of a small study using 24 healthy participants, which looked at whether eating a deep-fried Mars bar could affect the body's ability to respond to breath holding by increasing blood flow to the brain (termed "cerebrovascular reactivity"). Impaired cerebrovascular reactivity has been associated with stroke, but this latest study didn't look at stroke as an outcome.
Importantly, it found no significant differences in cerebrovascular reactivity after eating either a deep-fried Mars bar or porridge.
When the researchers analysed men and women separately, they also found no significant differences in cerebrovascular reactivity after eating a deep-fried Mars bar or porridge in either men or women.
However, when the researchers compared men with women, they found a significant difference.
Common sense suggests that eating deep-fried Mars bars regularly is not good for your health. However, this study didn't find any evidence that a deep-fried Mars bar alone can trigger a stroke within minutes.
The deep-fried Mars bar - a short history
The first deep-fried Mars bar was reportedly first offered in 1995 by a chip shop on the outskirts of Aberdeen. A local journalist picked up on the story and it quickly went viral, being re-reported by both national and international media.
The dish soon became, as the authors of the current study put it, "a worldwide symbol of all that is wrong with the high-fat, high-sugar Scottish diet".
However, as many Scots will argue, it is mainly tourists who request the dish.
And before any English readers start feeling superior, that English takeaway staple the doner kebab usually contains far more saturated fat and calories than a deep-fried Mars bar.
Where did the story come from?
The study was carried out by researchers from the University of Glasgow and the British Heart Foundation Cardiovascular Research Centre in Scotland, and was funded departmentally.
The study was published in the peer-reviewed Scottish Medical Journal.
The media coverage of this story was poor. The oft-repeated claim that the snack can trigger a stroke within minutes is entirely baseless. Obviously, if you are recovering from a stroke or told that you have risk factors for a stroke, then a deep-fried Mars bar would probably be bottom of the list of recommended foods. However, it seems unlikely that a single sugary snack would trigger a stroke.
Causes of stroke are usually a combination of interrelated risk factors, such as smoking, high blood pressure, high cholesterol, obesity and excessive alcohol consumption.
What kind of research was this?
This was a randomised crossover trial that aimed to determine whether eating deep-fried Mars bars impaired cerebrovascular reactivity in comparison to eating porridge.
Cerebrovascular reactivity is the change of blood flow in the brain in response to a stimulus. In this trial, the researchers looked at the change in blood flow after participants were asked to hold their breath for 30 seconds. Holding your breath should increase blood flow to the brain.
The researchers say that impaired change in brain blood flow following a stimulus is associated with an increased risk of ischaemic stroke (stroke caused by a lack of blood flow to the brain).
In this randomised crossover trial, all participants ate both a deep-fried Mars bar and porridge. Half the participants ate the Mars bar first, and half the participants ate the porridge first. Whether they ate the Mars bar first or the porridge first was randomised.
A randomised crossover trial is an appropriate study design to answer this sort of question.
What did the research involve?
The researchers studied 24 people, with an average age of around 21. Their body mass index (BMI) was within the healthy range (an average of 23.7).
After fasting for at least four hours, people were randomised to receive a deep-fried Mars bar or porridge.
The researchers looked at changes in blood flow in the brain after participants held their breath for 30 seconds, before and 90 minutes after, eating either a deep-fried Mars bar or porridge.
They looked at blood flow using ultrasound.
Participants returned to receive the other foodstuff on a second visit at least 24 hours after the first.
The researchers compared the changes in blood flow after participants ate the deep-fried Mars bar and porridge.
What were the basic results?
Eating a deep-fried Mars bar caused a non-statistically significant reduction in cerebrovascular reactivity compared to eating porridge.
The researchers then looked at men and women separately (14 of the 24 people in the study were male). Changes in cerebrovascular reactivity were not significant in either men or women after they ate a deep-fried Mars bar or porridge.
The researchers then compared men with women. They found there was a significant difference in cerebrovascular reactivity after eating a deep-fried Mars bar compared to eating porridge, with a modest decrease of cerebrovascular reactivity in males.
How did the researchers interpret the results?
The researchers concluded that, "Ingestion of a bolus of sugar and fat caused no overall difference in cerebrovascular reactivity, but there was a modest decrease in males. Impaired cerebrovascular reactivity is associated with increased stroke risk, and therefore deep-fried Mars bar ingestion may acutely contribute to cerebral hypoperfusion [decreased blood flow] in men."
This study found no significant differences in cerebrovascular reactivity (the body's ability to respond to breath holding by increasing blood flow to the brain) after eating either a deep-fried Mars bar or porridge.
When the researchers analysed men and women separately, they found no significant differences in cerebrovascular reactivity after eating a deep-fried Mars bar or porridge. However, when the researchers compared men with women, they found a significant difference, although whether there is any clinical significance to this finding is unclear.
The researchers point out that there are limitations to their study, including the fact they studied young, healthy individuals. It may be that there are differences in cerebrovascular reactivity in older patients at risk of stroke.
Confirming whether the risk is significant in this sub-group would be challenging, not least due to ethical considerations. Assigning people a diet you suspect could harm them would be a serious breach of medical ethics.
Common sense suggests that eating deep-fried Mars bars regularly will not be good for your health, as a diet high in saturated fats and sugar can increase the risk of cardiovascular diseases (diseases that affect the heart and blood vessels).
However, the very occasional late night "guilty pleasure" is highly unlikely to trigger a stroke.
"Eating a deep-fried Mars bar could give you a stroke in minutes," reports the Metro. However, the study that prompted this headline found no evidence that the Scottish snack can potentially trigger a fatal stroke within minutes...
Links to Headlines
Deep-fried Mars bar raises risk of having a stroke WITHIN MINUTES, experts claim. Daily Mirror, September 29 2014
Deep-fried Mars bars 'could trigger a stroke': Blood flow to the brain slows within minutes of eating the snack. Mail Online, September 29 2014
Eating a deep fried Mars bar could give you a stroke in minutes. Metro, September 29 2014
Links to Science
Dunn WG, Walters MR. A randomised crossover trial of the acute effects of a deep-fried Mars bar or porridge on the cerebral vasculature. Scottish Medical Journal. Published online September 22 2014
- NHS Choices links
- Causes of stroke
- Preventing stroke
- Stroke - real stories
- Editor's pick of the blogs
- Evidently Cochrane
- Research the Headlines
- Science blog - Cancer Research UK
- Science Media Centre
- Sense about Science