The deep-fried Mars bar is often cited as an illustration of what is wrong with a high-fat, high-sugar diet, particularly in Scotland, where the deep-fried Mars bar is apparently popular with research showing it is served in approximately 22% of chip shops. Scotland has had the second highest mortality from stroke in Western Europe over the past half century, and although links between diet and disease are increasingly made, the link between nutrition and stroke is not clear. In this context, researchers from Glasgow University decided see if the apocryphal deep-fried Mars bar, as an example of a dietary bolus of fat and sugar, could change cerebral blood flow immediately after consumption.
Twenty-four healthy young adults (14 men, 7 women, average age 21 years) were randomized to receive a deep-fried Mars bar and then porridge as a control or vice versa. Compared with porridge, consumption of the deep-fried Mars bar caused no overall difference in cerebrovascular reactivity (CVR), which is a risk factor for stroke. Interestingly, however, there was a significant impairment in CVR in the men. Impaired CVR is associated with reduced cerebral blood and with increased risk of stroke. The porridge produced no change in CVR.
Given the small number of study participants, these findings would need to be replicated in a larger study. However, the researchers controlled for wider circulatory changes in their study, such as those that occur normally after a meal, which adds weight to their findings. The change in CVR found in this study would have little impact on stroke risk in this young healthy male population but could increase risk of stroke in older men, particularly those at risk for other reasons.
How a high fat, high-sugar dietary bolus can reduce CVR in men and not women is unclear. In their conclusions the authors say that a larger study should be conducted in men alone, which might help to identify the possible mechanism for this change in cerebral blood flow. Evidence exists that deep frying fish negates the cerebrovascular benefits of eating fish and it could be that compounds formed during frying damage blood vessels in the brain.
In the meantime, perhaps we should stick with porridge or low sugar cereals at least for breakfast. If the temptation to try a deep-fried Mars bar is strong, maybe share one with friends in a Scottish restaurant where they are sometimes served as a delicacy!