Can a low carb diet cause anxiety?

Yes they can. Because you are not getting in much if any carbohydrates your blood sugar remains very low, because your body and particularly your brain prefers to run on glucose the body is forced to make it's own, to do this it has to release hormones to assist in gluconeogenesis (the creation of glucose) these hormones are our bodies ''fight or flight'' hormones mainly cortisol and adrenaline. With these hormones circulating the body it can cause people to feel all the lovely feelings that come along with anxiety.

Another factor at play is serotonin levels, in people with anxiety and depression it's been shown that they have low levels of serotonin in the brain. Carbohydrates help in the creation of serotonin and depleting them from your diet will also deplete serotonin levels.