Mediterranean diet can protect your brain as you age
Mediterranean diet may protect your brain as you age, new evidence suggests
Amid the controversy over diets and detoxes, sugars and fats, there's at least general agreement that a Mediterranean diet — fruits, veggies, 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 with it. The researchers found that over a three-year period — from age 73 to age 76 — adherence to a Mediterranean diet was 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 2.5 ml (half a teaspoon) - and accounts for a very small fraction of the total volume variability. But who's to say what you might accomplish with that extra half-teaspoon of brains? If these results prove reliable, there's certainly an incentive to stock up on family-sized olive oil bottles.
We already have evidence that the Mediterranean diet, and specifically higher fish and lower meat consumption, is associated with larger brain size. However, associations between lifestyle and the brain are difficult to interpret because a causal connection is equally credible in both directions. That said, if I eat healthily and have a big brain, my diet may be good for my brain or my big brain may help me maintain my diet. Or there's something I haven't measured, something that affects my brain and diet separately. For example, if I live a comfortable, affluent, and stress-free life, it might be good for my brain and make eating healthy easier at the same time. If that's the case, finding a healthy connection between diet and a big brain doesn't mean they're directly related.
These are critical considerations. Citing evidence in support of lifestyle changes requires knowing the exact lifestyle changes that are required and what the exact benefits may be. This is why randomized controlled trials are so attractive. If you have two well-matched groups, subject them to two controlled dietary interventions, and do a before-and-after analysis, you have firmer ground when you claim that the dietary intervention played a direct role in bringing about the changes.
Although the researchers did not conduct a randomized trial in this latest study, they still provided important insights by collecting replicate data that allow them to estimate brain size not in terms of absolute values but in terms of changes over time to compare.
At age 70, participants gave a detailed account of their dietary habits. On this basis, they could be characterized as "high" and "low" in their adherence to a Mediterranean diet. Three years later, they had a baseline brain scan, and another three years later, brain changes from that baseline were assessed with a second brain scan, allowing each participant to serve as their own control. This is a powerful approach, and in addition to using the first scans to confirm that brain volume is actually larger in people who adhere more closely to the Mediterranean diet, they found that it increased between the ages of 73 and 76 Loss of brain volume gave those with low diet adherence. This remained significant when considering a number of highly relevant factors related to age, gender, health, body weight, education and aspects of mental functioning.
Interpret with caution
These findings are consistent with the encouraging possibility that proper nutrition has a real impact on brain tissue loss. But the authors are cautious, and rightly so. First of all, their findings are not entirely consistent with previous studies on the effects of diet on the brain. For example, they could not find previously observed effects of higher fish and lower meat consumption. It becomes difficult to say whether it is diet as a whole or specific components of it that might exert the positive effect on brain size.
The analysis also shows that cognitive function did not differ significantly between diets, raising the question of how useful it might be to alter brain loss to this extent.
As the researchers admit, they also ran several statistical tests to look for significant associations — those with a low p-value (the likelihood of finding that difference when there's no real difference in brain size) — and came up with them they found the reduction in brain loss. But if you take all of these searches into account and pick a significant association (brain volume) from non-significant ones (eg, a lack of change in gray matter volume), you increase your chances of inadvertently attributing meaning to something that happens by chance.
Although the authors have made nice attempts in their design and analysis to exclude potentially complicating factors, there is bound to still be some ambiguity about cause and effect here. They previously showed in another study that an apparent relationship between a Mediterranean diet and cognitive functioning later in life could actually be explained by childhood IQ.
While the current analysis ruled out a similar explanatory role of a more restricted IQ measure and a panel of mental function tests, we must consider the possibility that there are other factors, not considered here, that relate separately to diet compliance could and brain volume and would therefore create the illusion of dietary influence on the brain. For example, it is not clear whether excessive alcohol consumption could be associated with a non-Mediterranean diet. Or maybe physical activity could also play a role.
But at the same time, there are reasons why this finding — that following a Mediterranean diet results in less brain loss in older people — might be even stronger than the numbers suggest. The participants were divided according to the general style of their diet. So some in the high and low diet groups would actually have been fairly close to midpoint and therefore less likely to have a large impact. One might imagine that there could be even greater effects on brain size by taking two groups that more exemplify the Mediterranean and non-Mediterranean diets. We will see. Definitely keep eating the legumes. Even though it turns out that the Mediterranean diet doesn't stop your brain from shrinking, there are plenty of other benefits to be had. THE CONVERSATION
Bernard Wolfe Professor of Health Neuroscience, University of Cambridge