Here is a curious fragment... Brinkworth et al. studied 106 obese people put on either a low fat or low carbohydrate diet for a year, doing psychological assessment tests during this period. Initially, shedding pounds put both groups in a better mood. But, in the low carbohydrate group this effect began to wear off after the first few weeks. Over 1 year, there was a favorable effect of an energy-restricted low fat diet compared with an isocaloric low carbohydrate diet on mood state and affect in overweight individuals, but both diets had similar effects on working memory and speed of information processing.