An MIT study suggests that low-car/pro-protein diets like Atkins can chemically bum you out. Judith Wurtman, director of the Program in Women's Health at the MIT Clinical Research Center, found that when you kick the carb habit, your brain stops regulating serotonin. As people who take SSRI drugs like Prozac know, serotonin elevates mood and can also act as an appetite suppresant.
"According to Wurtman's clinical studies, if the carbohydrate craver eats protein instead, he or she will become grumpy, irritable or restless. Furthermore, filling up on fatty foods like bacon or cheese makes you tired, lethargic and apathetic. Eating a lot of fat, she said, will make you an emotional zombie."Link