5 healthy foods to help you kick your vending machine habit and boost productivity

Ever noticed that when you're stressed, you indulge in food that you know is bad for you?

It's a phenomenon that affects many professionals, according to numerous scientific studies.

"When we are stressed, our body can crave comfort foods," says Marlynn Wei, a Harvard and Yale-trained psychiatrist, "foods high in salt and fat that don't have the kind of nutrients that your mind needs for a better mood long-term."

Considering that the average employee is working longer hours, foregoing vacation and feeling disconnected at work, it's no wonder so many stressed-out workers find eating healthy difficult.

It also doesn't help that foods high in fat, cholesterol and sugar give the brain instant gratification, which can become addicting. A growing body of research shows that eating poorly makes people feel sluggish and less mentally sharp.

"Put simply, what you eat directly affects the structure and function of your brain and, ultimately, your mood," writes Harvard Medical School professor and board-certified doctor Eva Selhub.

The good news is that certain foods have been shown to boost cognitive function and one's mood.

Here are 5 foods to help you kick your bad eating habits and make you feel energized at work:

Following a Mediterranean diet, which includes whole grains and hummus, has been shown to reduce memory loss and keep a person's learning abilities sharp.

According to a study published in the American Academy of Neurology, older people who followed the diet over a three-year period retained more brain volume, associated with brain function, than those who did not. It's one of multiple that support the thesis.

Research associated with Harvard Medical School found that women who ate five or more servings of nuts per week performed better in a various cognitive tasks than those who did not.

"Higher nut intake may be related to better overall cognition at older ages," the researchers write.

While nuts in general are good for your brain, walnuts specifically have been shown to keep people mentally sharp, according to the Journal of Nutrition. In one study, mice with Alzheimer's disease who were regularly fed walnuts showed increase memory, motor skills and learning abilities.

Scientists at UCLA have found a correlation between consumption of probiotics found in yogurt and increased cognitive function.

Their research found that healthy women who ate yogurt twice a day showed positive changes in the parts of the brain that process emotion, indicating that the probiotics in yogurt could help your mood.

"Blueberries and other berries have been found to protect the brain," says Wei.

Blueberries could improve your memory and reverse memory loss, according to one animal study from Tufts University. Another study, conducted on older adults by researchers at the University of Cincinnati, found similar results.

While you won't want to keep a desk drawer full of dark chocolate, having it occasionally, or mixing it with some of other foods on this list, could be a good thing.

Dark chocolate has a high concentration of flavanol-rich cocoa, which has been shown to "improve verbal fluency and cognitive function" in elderly people, according to a study published by the American Heart Association. Other research shows that having a daily portion of dark chocolate improves blood flow to the brain.

Check out the 2-minute exercise a Harvard-trained psychologist says will help you relax at work

Video by Rajaa Elidrissi.