A new study shows that a blueberry smoothie at breakfast can stop you flagging in the afternoon.
Researchers found that a large helping of the fruit - described by some as nature's 'superfood' - boosts concentration and memory up to five hours later.
The study, reported at the British Science Festival, also claims that blueberry can help fight dementia in the long term.
British scientists who made the discovery believe the antioxidants in blueberries stimulate the flow of blood and oxygen to the brain - and keep the mind fresh.
Dr Jeremy Spencer, a molecular nutritionist at the University of Reading who carried out the latest study, said: "I think that the findings were impressive and have the potential in the long term to lead to cognitive improvement."
To reach the conclusion, the researchers tested the fruit's powers on a group of 40 adults made up of students aged between 18 and 30, reports The Telegraph.
The group was given a set diet, which included a blueberry smoothie, and then asked to do a number of exercises to test their powers of concentration throughout the day.
A month later they were brought back and given the same diet and tests but without the smoothie.
Researchers found that while there was no change in the cognitive powers between the two occasions for the first few hours, towards the end of the day the smoothie stopped the concentration flagging, while without it dropped by up to 20 per cent.
"After one hour there was little difference in the attention tests but after five hours people who did not have the smoothie's performance dropped by 15 to 20 per cent," said Spencer.
The results were repeated with another group of 40 volunteers, this time pensioners.
He said that he was now concentrating on the long term effects of eating blueberries and particularly their effect on the hippocampus, the part of the brain related to memory.