Amid the contention about diets and detoxes, sugar and fats, there is at least general agreement that a Mediterranean diet – fruit, vegetables, olive oil, grains, fish – is a good thing. Now, a new study based on brain imaging in over 400 people seems to show that we have even more reason to celebrate this diet and, more importantly, to stick to it. The researchers found that over a three-year period – from the age of 73 to 76 – adherence to a Mediterranean diet is associated with a reduction in the inevitable loss of brain volume that occurs with age.
The difference in volume loss associated with the diet is not large – about 2.5ml (half a teaspoon) – and it only accounts for a very small fraction of overall volume variability. But, who’s to say what you might achieve with that extra half teaspoon of brain? If these results prove reliable, there is surely an incentive to stock up on family-sized bottles of olive oil.
We already have evidence that the Mediterranean diet, and particularly higher fish and lower meat consumption, is associated with increased brain size. But it’s hard to interpret associations between lifestyle and the brain because a causal relationship is equally credible in both directions. That is to say, if I eat healthily and have a big brain, it might be that my diet is good for my brain or my big brain is good at helping me maintain my diet. Or there may be something that I haven’t measured, something that influences my brain and my diet separately. For example, if I live a comfortable, affluent, stress-free life perhaps this is simultaneously good for my brain and facilitates my healthy diet. If so, finding a healthy association between diet and a big brain does not mean that they are directly related.
These are critical considerations. Citing evidence to support lifestyle changes demands that one knows the precise lifestyle changes needed and what the precise benefits may be. This is why randomised control studies are so appealing. If you have two well-matched groups, subject them two controlled dietary interventions, and do a before and after analysis, you are on firmer ground when asserting that the dietary intervention has had a direct role in producing the changes.
While the researchers in this latest study did not carry out a randomised trial, however, they have nevertheless provided important insights by gathering repeat data, allowing them to compare brain size not in terms of absolute values but of changes across time.
At age 70, participants gave a detailed report on their dietary habits. On this basis, they could be characterised as “high” and “low” in their adherence to a Mediterranean diet. Three years later, they had a baseline brain scan and, a further three years afterwards, brain changes from this baseline were assessed with a second brain scan, so every participant served as their own control. This is a powerful approach and, as well as using the initial scans to confirm that brain volume is indeed greater in people who follow the Mediterranean diet more closely, they determined that, between the ages of 73 and 76 years, there was a greater loss of brain volume for those with low adherence to the diet. This remained significant when taking into account a number of highly relevant factors relating to age, sex, health, body weight, education and aspects of psychological functions.