Feeling grouchy? Your low-carb diet could be to blame, according to two Massachusetts Institute of Technology (MIT) researchers who have looked at carbohydrates and brain chemistry.

Husband-and-wife researchers Judith and Richard Wurtman have discovered that after a person consumes sweet or starchy carbohydrates, with little protein, the brain makes serotonin, a chemical that elevates mood. They also found the inverse to be true: when one stops eating carbohydrates, the brain stops regulating serotonin.

The Wurtmans also found the brain actually sends out signals to eat carbohydrates and that if the carbohydrate craver eats protein instead, he or she will become grumpy, irritable or restless.