Summary: The low-carb plan can lead to irritability and mood swings.

Do the chips that don't pass the lips of low-carb dieters weigh heavily on their shoulders instead? People who avoid certain foods or are reducing their food intake are famous for irritability, but many who are testing low-carbohydrate approaches like Atkins and the South Beach Diet are reporting unusually high feelings of anger, tension and depression. "It's called the 'Atkins attitude,' " says Judith Wurtman, director of the Women's Health Program at the Massachusetts Institute of Technology and the Adara Weight Loss Center, both in Boston. "It's very well-documented." Wurtman, who advocates a diet high in complex carbohydrates for weight loss and stress relief, says her studies on rats have shown a connection between a diet low in carbohydrates and low levels of serotonin' neurotransmitter that promotes feelings of happiness and satisfaction. In her research, rats placed on a ketotic, or low-carbohydrate, diet for three weeks were found to have lower levels of serotonin in their brains. The same rats binged once starch was reintroduced into their diets.

Wurtman believes that same effect occurs in humans on low-carb diets and leads to pronounced feelings of depression and sadness, even rage. "People feel very angry, and their antidepressants don't work well, either," she says.

Granted, dieting isn't easy no matter how one does it, but many think low-carbohydrate approaches are particularly hard on your happiness. Wurtman goes so far as to call them dangerous for those who already struggle with depression or bipolar disorder.