Diet and brain health

A healthy diet has long been recognised as having a role in preventing diseases like type two diabetes and heart disease. Could it also have a role in brain health as we age? Dr Michelle Luciano of the University of Edinburgh brings the research findings together, as part of our Staying Sharp series.

Diet

Food is not only vital for life but also a source of great pleasure for our taste buds and when enjoyed in the company of family and friends. Its importance in keeping us healthy has been recognised for centuries. In medicine, it is well known, for example, that salt raises blood pressure and that saturated fats increase cholesterol.

Evidence is now accumulating that supports a link between diet and brain processes such as our thinking, or cognitive, skills. Specific nutrients in food - such as omega-3 fatty acids, flavonoids, vitamins B, D and E, and choline - have been associated with improved cognitive function in older people. Such dietary factors can affect the way our brain cells communicate and this may be the reason for the effects on cognitive function.

Dietary patterns

More recently, researchers have been interested in the effects of dietary pattern rather than specific food components and their nutrients.

One dietary pattern that has repeatedly shown positive effects for health is the Mediterranean diet, traditional in olive growing regions of the Mediterranean. In the 1960s, people from these regions had very high life expectancy and low rates of coronary heart disease and certain cancers. The diet is characterised by:

• high intake of fruit, vegetables, cereals or cereal-based foods (for example wheat, oats, corn, rice) and legumes (for example peas, beans, lentils)
• moderate intake of alcohol (usually wine) and fish
• low-to-moderate intake of dairy products
• low intake of meat (red and poultry)
• a high monounsaturated to saturated fat ratio, which can be achieved through high consumption of olive oil rather than other fats

This type of diet helps avoid high levels of saturated fat as it is not rich in components such as butter, other dairy products, palm oil and meat.

While the general health benefits of this diet are already recognised, research is now also indicating that increased adherence to a Mediterranean diet is associated with better cognitive functioning in old age, and lower risk of dementia and Alzheimer’s disease. This is emerging from studies that measure people’s typical food intake at the start of the study and measure their cognitive function at the start and then on subsequent occasions over a period of time. This enables measurement of changes in their cognitive function over time.

Mediterranean diet and the brain

Cognitive functioning is dependent on a healthy brain, so in our own research we measured the effect of adherence to a Mediterranean-type diet on the volume of the brain in Scottish people who were free of dementia. This was the Lothian Birth Cohort 1936, the participants in the Age UK-funded Disconnected Mind research project. We gathered diet information from them at age 70 and scanned their brains at ages 73 and 76 so that we could look specifically at change in brain volume over time.

We found that people who did not follow as closely to the Mediterranean diet were more likely to have a higher loss of total brain volume over the three years than people who followed the diet more closely.

In future studies, we will test whether the change in brain volume is linked to change in cognitive functioning.

Should we hop on the ‘Mediterranean diet’ bandwagon?

The studies supporting positive effects of a Mediterranean diet on brain health are mostly correlational. This means that they measure an association between this type of diet and an aspect of brain health, but cannot determine whether the diet is a direct cause of the observed change in brain health.

In turn, this means it is too early to tell whether we should hop on the ‘Mediterranean diet’ bandwagon right now for our brain health.

However, there are other good reasons to do just that (though without the alcohol component for those who don’t drink), not least that many aspects of the diet are consistent with current nutritional advice, as well as the possibility that it may be good for the brain.

The future

To establish whether the Mediterranean diet has a direct effect on brain health, a type of study, known as a randomised control trial, is needed. In such trials, different groups of people would be put on different diets for a period of months or longer and their cognitive functioning would be repeatedly assessed over that time. In this way, the effects of a Mediterranean diet could be compared with a healthy ‘non-Mediterranean’ diet or a ‘control’ group who have received no change to their diet.

Further trials could test specific components of the Mediterranean diet (e.g. increasing olive oil consumption) to establish whether there are individual components that are beneficial to health or whether it is the combination of components in the diet that is beneficial.

Where next?

Key references

• Gómez-Pinilla, F., 2008. Brain foods: the effects of nutrients on brain function. Nature Reviews Neuroscience, 9(7), pp.568-578.
• Luciano, M., Corley, J., Cox, S.R., Hernández, M.C.V., Craig, L.C., Dickie, D.A., Karama, S., McNeill, G.M., Bastin, M.E., Wardlaw, J.M. and Deary, I.J., 2017. Mediterranean-type diet and brain structural change from 73 to 76 years in a Scottish cohort. Neurology, pp.10-1212.
• van de Rest, O., Berendsen, A.A., Haveman-Nies, A. and de Groot, L.C., 2015. Dietary patterns, cognitive decline, and dementia: a systematic review. Advances in nutrition: an international review journal, 6(2), pp.154-168.
• Willett, W.C., Sacks, F., Trichopoulou, A., Drescher, G., Ferro-Luzzi, A., Helsing, E. and Trichopoulos, D., 1995. Mediterranean diet pyramid: a cultural model for healthy eating. The American journal of clinical nutrition, 61(6), pp.1402S-1406S.