Low carb should technically be bad for mood.
Carbs help you feel very satiated and also help in the production of serotonin in the brain. Tryptophan is turned into serotonin when in the brain, but needs carbs are required for it to happen:
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Plenty of carbohydrates in your meals helps tryptophan get to where it does the most good: your brain. In order to cross the blood-brain barrier and get in, carbs are required. So cheese and crackers provides a better effect than the cheese standing alone. Cover your ears, animal friends, for I am also about to condone eating the occasional dead bird. Poultry, especially the dark meat, is a rich (yet very cheap) source of tryptophan. Add potatoes or stuffing, and you have the reason everybody is sprawled out and snoring up a storm after a typical Thanksgiving food orgy. But to be able to look your parakeet in the eye after the fourth Thursday in November, you can stay vegetarian and still get tanked up on tryptophan.