Are you feeding your brain the right kind of fatty diet? Dairy products such as cheese and milk are among the most reviled of foods, with many experts saying their links to heart disease and obesity mean we should shun them when possible.
But new research has caused controversy by suggesting that, in fact, dairy food could be essential for a healthy brain.
The study, by U.S. and Australian researchers, involving 1,000 adults, found those who regularly have dairy products such as milk, cheese and yoghurt score better on tests of mental ability than people who never, or rarely, consume dairy.
Although the research, published in the International Dairy Journal, needs following-up, as it did not conclusively establish the link between dairy and fatty diets and brain power, it highlights an intriguing line of research.
It follows another U.S. study, involving 104 pensioners, where scientists found older people with higher levels of beneficial fats in their blood had less brain shrinkage typical of Alzheimer’s disease. These beneficial fats — omega-3 essential fats — are found in foods such as oily fish. The research, published in Neurology, the journal of the American Academy of Neurology, is key, as it measured the levels of different fats in people’s blood, rather than simply relying on their reports of what they tended regularly to eat.
It’s now well established from brain-tissue studies that our mental functions depend heavily on a good supply of fat.
Our brain is composed of 60 per cent fat. The brain cells are insulated by sheaths of myelin composed of 75 per cent fat. This myelin fat needs to be replaced constantly.
Myelin sheaths are vital to the cells’ ability to communicate. It’s thought the more myelin you have, the quicker you learn new skills.
Significantly, in a disease such as multiple sclerosis, the myelin sheaths are damaged, affecting how messages are transmitted in the brain and causing symptoms such as numbness and paralysis.
This research on the brain confronts the common view about the dangers of dietary fat. So strong is the negative message that studies show up to 40 per cent of all UK adults try to avoid fat for health reasons.
But, in fact, the benefits of avoiding fats might not be so clear-cut.
For example, a study of older people in the British Medical Journal found that those on low-cholesterol diets have a far higher rate of stroke, possibly because cholesterol seems to have a protective effect in mature brain linings.
Meanwhile, a California University study published in The Lancet reports a link between low-fat diets and increased incidence of depression among men aged over 70.
It suggests this may be because low cholesterol levels shorten the amount of time the feel-good hormone serotonin is effective.
Studies also show fat in diets may help the brain to suppress harmful behavioural impulses: monkeys have been found to become abnormally aggressive when put on low-fat diets, according to a report in the journal Psychosomatic Medicine.
But rather than investigating such discoveries further, the medical establishment has ignored or discredited them, for fear of confusing the ‘dietary fat is bad’ message.
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So, which fats seem to help best?
When it comes to the benefits of dairy on the brain, more research is needed. But there’s a large body of research to show that omega-3 and omega-6 fats are vital for the brain.
You might think you knew this already. And, indeed, a few years ago there was much-publicised research to suggest that omega-3 supplements were good for the brain. But that research has since been dismissed as unscientific (also, it’s not supplements, but getting the fats from food that counts).
Now a number of new, more authoritative studies have shown how omega-3s help by developing and protecting myelin. Our bodies cannot make these fats, so they need to get them from diet.
An important substance in these fats is DHA (docosahexaenoic acid) which the body derives from omega-3. This helps preserve the brain’s health in older age.
The best sources of DHA are oily fish, such as salmon, wholegrains and dark green, leafy vegetables.
A study published in the journal Archives of Neurology found that people with the highest levels of DHA in their blood had a 50 per cent lower risk of developing dementia from any cause.
After nine years of follow-up, they were also shown to be less likely to develop Alzheimer’s.
DHA has been found to help the brains of developing babies, too.
A study in the American Journal of Clinical Nutrition found the children of women who had high levels of DHA in their red blood cells around the time they gave birth scored above average on the intelligence tests at age six.
But, interestingly, the study says this effect resulted from the mothers eating diets rich in fish and DHA, rather than supplements.
This may help to explain why studies of pregnant women taking only fish-oil supplements have often failed to provide conclusive evidence of benefits in their offspring.
The Spanish experts behind this research speculate that this might have something to do with the way our bodies absorb and process foods that feature regularly in our diet.
Sources of omega-6 fatty acids include seeds, nuts and their oil.
So, why would fats be so crucial to the human brain? Our brains grew to their present proportions a million years ago. Before that, our body-to-brain size ratio was similar to other primates. For years, scientists have puzzled over what caused this growth.
Dr David Braun, an anthropologist and archaeologist at the University of Cape Town, South Africa, has suggested the fish-eating habit of primitive humans were responsible. He says we started to eat fish about two million years ago in the Great Rift Valley in Africa, thought to be the cradle of our species, and this enabled us to grow brains that were much bigger and more efficient than rival species.
But there’s another side of the coin. While omega fats seem crucial, they can be displaced from our brains by trans fats, found in baked and fried goods and fast food.
While the scientific case for omega fats’ dietary benefits is growing stronger, so, too, is the argument against trans fats in our diets at all.
A study of children growing up in the Avon area, for example, has shown that a diet high in processed fats may lower IQ.
The study, following 4,000 children from birth to the age of eight-and-a-half, found those who ate diets high in processed fats showed significantly lower IQ scores at the older age than those whose diets had been high in healthy fats.
The results echo earlier research. For example, a study of children who ate margarine high in trans fats (hydrogenated vegetable oils) every day showed that they had lower IQs than those who did not.
Meanwhile, last year’s study in the journal Neurology, which reported that pensioners who ate lots of omega fats were less at risk of Alzheimer’s, also found the reverse effect with trans fats.
People whose blood-nutrient levels showed they had junk-food diets showed more of the brain-shrinkage associated with dementia.
Furthermore, studies on rats, by neuroscientist Lotta Granholm, have shown that trans fats impair memory and learning.
Granholm, the director of the Centre on Ageing at the Medical University of South Carolina, says trans fats seem to destroy proteins that help brain cells to communicate. ‘After I did this study, I didn’t eat french fries any more,’ she says.
Dr Alex Richardson, a research fellow at the University of Oxford and an authority on the impact of nutrition on the brain, is particularly concerned by trans fats. ‘They should have been banned years ago,’ she says. ‘They are toxic.’
One of the most damaging things about these fats, she adds, is that they actually stop essential fats, such as omega-3, from being absorbed in the brain.
‘There’s good evidence trans fats alter the signalling ability of the brain’s chemical messengers. If you give these to children, you’re replacing essential fats that make their bodies and brains work properly with ones that clog the machinery.’
In order to protect our brains and those of our children, it appears that we have to become fat-headed — but only with the right sort of fats.