Academics in Australia tested a group of people who ate a diet high in sugar and fat and low in fruit, vegetables and fibre and another group who ate more healthily.
They found that those on the unhealthy Western-style diet were slower at learning and had a poorer memory than those who ate a healthier diet.
The poor diet group also showed a smaller reduction in the desire for snacks when they were full as opposed to hungry.
This effect, reported at the Society for the Study of Ingestive Behaviour’s annual meeting in Portugal, has been seen in experiments on animals before.
It is thought the Western diet affects the hippocampus area of the brain, hindering the ability to block out memories that are no longer useful.
Normally memories of food are at the forefront of your mind when you are hungry, but are blocked when your body feels full.
But this process does not seem to work as well among those who eat a diet high in fat and sugar.
Researcher Tuki Attuquayefio, of Macquarie University, said: “Even though they were full, they still wanted to eat the sweet and fatty junk food.
“What was even more interesting was that this effect was strongly related to their performance on the learning and memory task, suggesting that there is a link between the two via the hippocampus.”
Previous research has suggested that middle-aged adults who are overweight and obese are at greater risk for developing Alzheimer’s disease and other forms of dementia compared to people of normal weight.
And children as young as seven may suffer from an impaired memory because of a fat and sugar-rich Western diet.
Studies in rats have shown that the Western diet can weaken the blood-brain barrier, which helps protect the brain from harmful agents in the bloodstream.
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