The aging brain is a shrinking brain, and a shrinking brain is, generally speaking, a brain whose performance and reaction time are declining: That is a harsh reality of growing older.

But new research shows that brain shrinkage is less pronounced in older folks whose diets hew closely to the traditional diet of Mediterranean peoples -- including lots of fruits, vegetables, legumes, nuts and olive oil, little red meat and poultry, and regular, moderate consumption of fish and red wine.

In a group of 562 Scots in their 70s, those whose consumption patterns more closely followed the Mediterranean diet experienced, on average, half the brain shrinkage that was normal for the group as a whole over a three-year period.

To glean how diet might influence brain aging, researchers tapped into a large group of Scottish people who were all born in 1936 and had many measures of health status and lifestyle tracked from an early age.


Around the time they reached age 70, 843 members of the “Lothian Birth Cohort” filled out a dietary frequency form that gave researchers a broad look at what foods they ate, which they avoided, and how often they consumed them. At about age 73 and again around age 76, their brains were scanned to gauge the volume of the overall organ and a few of its key components.

The researchers used the food-frequency surveys to divide the group into two — those who at least approximated a Mediterranean-style diet and those who came nowhere close. Even though many in the Med-diet group were far from perfect in their adherence, the average brain-volume loss differed significantly between the two groups.

Findings on the impact of Mediterranean diet on healthy aging have been pretty strong — this is generally a good way to eat. Studies large and small have established that following a Mediterranean diet is effective at driving down heart attack, stroke and premature death risks, and improving the health conditions -- including hypertension, worrisome cholesterol levels and metabolic problems -- that raise those risks.

But researchers are less sure of the particulars of how the diet promotes better health.


In recent years, studies have sought to tease out not only how great the benefits are, but how they work: whether healthier brain-aging is a function of better vascular health or preserved brain volume, and whether the diet’s advantages lie in its dearth of red meat, the positive effects of the fatty acids in fish or olive oil, or the combined benefits of its plant-based foods.

Researchers also must demonstrate that, in their measurements of dietary intake and health, they’re not actually capturing well-understood relationships between intelligence, education and long-term health: People with certain cognitive strengths do better and stay longer in school and earn more; yes, the better educated and paid may consume healthier diets, but they are generally healthier anyway, so maybe the healthier diet is incidental.

The newest study, published Wednesday in the journal Neurology, helps untangle many of those mysteries. But it also leaves many questions unanswered.

Contrary to some research findings on the Mediterranean diet, the findings suggest that reduced brain shrinkage is not specifically linked to low intake of meat and high intake of fish. Maybe, the authors suggest (and many researchers believe this), the magic in the Mediterranean diet is all those plant-based foods, acting collectively to improve subjects’ cognitive health.


The study also finds that subjects across the spectrum of intellect and educational attainment reaped the benefits of the Mediterranean diet in reducing brain shrinkage (or, alternatively, suffered the effects of diets that departed sharply from that diet’s emphasis on plants, fish and polyunsaturated fats). That suggests the researchers are not wrongly crediting subjects’ dietary choices for advantages that may actually stem from higher intelligence and educational attainment.

Finally, the researchers wrote, the study’s design helps establish that the brain-shrinkage rates seen are likely to be the result of dietary patterns, and not just an association. That’s because the subjects’ dietary patterns were measured first, about the time that participants reached 70 years old. Their brain volumes were then measured by imaging scans three and six years later.

Assuming that people did not dramatically change their dietary patterns — a shift that is considered unlikely for folks in their 70s — researchers believe that the dietary habits that Scots reported as they entered older age played some role in the brain changes they detected further down the road.

Left unexplored here is whether a midlife shift toward the Mediterranean diet could have the same effects, or whether the group differences in brain volume are the rewards or penalties for a lifetime of dietary choices.


There’s good evidence that, when it comes to making better dietary choices, earlier is better. In a 2013 study of more than 10,000 women, researchers found that those who followed a Mediterranean-style diet in their 50s and 60s were about 40% more likely to live past the age of 70 without chronic illness and without physical or mental problems than were those with less-healthy diets.

melissa.healy@latimes.com

Follow me on Twitter @LATMelissaHealy and “like” Los Angeles Times Science & Health on Facebook.

MORE IN SCIENCE


With snow piling up in the Sierra, what will it take to end California’s drought?

Research on gun violence is severely underfunded compared with other causes of death

In a first, scientists detect ‘fast radio bursts’ from beyond the Milky Way galaxy