Reaction time and mood were improved in young individuals that consumed blackcurrant berry drink with 500 mg of polyphenols compared to placebo in a small pilot randomized controlled trial. EEG data also showed the blackcurrant drink changed brainwave activity.
This was a small trial with a crossover study design, which means each person serves as their own control. Both the blackcurrant drink and the placebo drink had 6.98 g of sugar (glucose +fructose). They also both had the same amount of vitamin C…the only difference was that the placebo drink lacked the 500 mg of polyphenols.
Conclusions cannot be made from this trial alone since it was a small pilot trial. However, there is a growing body of clinical trials showing polyphenols positively affect brain function in both young and old individuals.
I understand that it would not be possible to make a placebo drink if the whole fruit was used…but I think it is better to consume the berries with the fiber which changes the way sugar is metabolized and also has benefits for the gut microbiome.