October 21, 2015

expert reaction to study looking at diet and brain shrinkage in an elderly US population

A study published in the journal Neurology has looked at a possible association between a Mediterranean style diet and brain size. They report that in a group of elderly people, they observed higher total brain volume as well as other specific measurements in those who had a stricter adherence to the diet.

Dr David McGonigle, Neuroscientist, Cardiff University, said:

“We’d all like to know more about the links between diet and brain health, particularly in old age. This study has an impressively large sample size with which to base its conclusions on. However, there are a couple of points to clarify:

“Firstly, ‘bigger’ isn’t necessarily ‘better’. We’re still uncertain about the exact link between differences in numbers of ‘brain cells’ on one hand, and measures of brain size that can be measured from structural MR scans. It’s like comparing the size of a box with the amount of objects you put in it; I’ve had boxes from Amazon that are mainly empty space, and others that are the same size but are packed full. At the moment, we only get to truly measure the ‘box’ or the volume in MR – not the density or packing of the cells that go into it. While the two probably vary together in normal development, that relationship may be fundamentally altered in the atrophy caused by aging.

“Secondly, the other quite striking finding was that, between the ‘low’ and ‘high’ adherence to diet groups, there were no significant differences in any of the tests of intelligence or cognition that the group applied. If the difference is significant for the population, we’d expect that to be reflected in some other measures: maybe a memory test, or an intelligence test. There doesn’t seem to be any accompanying effects here. So while the diet seems to protect against a small overall effect in brain shrinkage, the authors failed to find any effect of that shrinkage in their population. That’s not to say it doesn’t exist – just that there’s no evidence to support a behavioural effect of the differences in brain shrinkage between the groups. I look forward to seeing a more extensive testing of the population to try to uncover this relationship, if it’s there.”

Prof. Derek Hill, Professor of Medical Imaging Science, UCL, and CEO of IXICO, said:

“Brain shrinkage – or atrophy – is a natural consequence of aging, and this shrinkage proceeds more rapidly in people with cognitive impairment or Alzheimer’s disease. But brain volume can also change as result of other causes such as hydration or certain drug treatments. The authors have found slightly bigger brains in those people following a Mediterranean diet, than on other diets. The authors interpret this cross-sectional finding as having implications for longitudinal effects of change over time in brain volume due to aging or disease, and even suggest that the data demonstrates that a Mediterranean diet provides several years protection against brain shrinkage. However, it’s not possible to draw firm conclusions about changes over time, or any protective aspects of this diet, from cross-sectional studies like this.”

Prof. Tom Dening, Professor of Dementia Research, Institute of Mental Health, University of Nottingham, said:

“These are interesting findings and offer encouragement to people who think that the Mediterranean diet has preventive value in dementia. But there are some limitations, most obviously (as mentioned) that this is a cross-sectional study and can’t really tell us much about what is causing what. It is also worth noting that the standard deviations for brain volumes, that is, the amount of variation between individuals, are quite large so there is a lot of overlap between the groups. It is not as though the people who eat more meat and less fish end up with wizened prune-sized brains! Also worth noting that until the researchers start making statistical adjustments, there is not any difference between the brain volumes of the two dietary groups. Furthermore there do not appear to be any differences between the groups on cognitive test scores, so it could be asked whether brain volume is actually very important anyway. It isn’t a parameter that we measure routinely in clinical practice.”

Dr Michael Bloomfield, Clinical Lecturer in Psychiatry, MRC Clinical Sciences Centre and UCL, said:

“This new study, in a relatively large sample, has found evidence of an association between a healthy balanced diet and reduced brain loss in older age – which is very exciting.  However, as it’s a cross-sectional study we need to be careful in the conclusions that we can draw from it.  Some really interesting and important questions remain including “Is this a potential effect of a type of diet in older age or of eating healthily throughout life?” and “is there a particular ingredient that may be protective for the brain?”.  One possibility could be that one of these ingredients, perhaps a fish oil, might be interfering with brain inflammation – however that’s just one possibility of many and would need to be tested in further experiments.  For the time being, the advice from scientists would be that the best ways to stay healthy across life are to eat a healthy balanced diet, take regular exercise and not smoke.”

Prof. Martin Rossor, NIHR National Director for Dementia Research, University College London Hospitals (UCLH), said:

“This study adds to the increasing evidence of the health benefits of a Mediterranean diet. There is also increasing evidence that what is good for the heart is also good for the head. The authors have carefully assessed dietary intake and shown using magnetic brain imaging a difference in brain volumes, being larger in those adhering closely to a Mediterranean diet. As the authors acknowledge this is only a cross sectional study and to show a difference in atrophy i.e. progressive shrinkage, will require serial imaging.”

‘Mediterranean diet and brain structure in a multiethnic elderly cohort’ by Yian Gu et al. published in the American Academy of Neurology journal, Neurology, on Wednesday 21 October 2015.  

Declared interests

Dr David McGonigle confirms that he has no relevant interests and that Cardiff University is his only employer

Prof. Derek Hill: “Derek Hill is a founder and chief executive of IXICO plc, a company that provides image analysis capabilities to pharmaceutical companies testing drugs on patients with neurodegenrative diseases. IXICO has no link to the authors or funders of this research.”

Prof. Tom Dening: “I have no conflicting interests to declare.”

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