Health & wellbeing It's not just in the genes: the foods that can help and harm your brain Our diet has a huge effect on our brain and our mental wellbeing, even protecting against dementia. Day after day, the foods we eat are broken down into nutrients, taken into the bloodstream and carried up into the brain. Itâs no surprise that, conversely, other foods are harmful for the brain, slowing us down and increasing the risk of cognitive decline. Glucose is the only energy source for the brain, so itâs crucial that the brain gets enough of it. Brain Food: How to Eat Smart and Sharpen Your Mind by Lisa Mosconi is published by Penguin Life.