CHO & Serotonin

In regards to serotonin levels - is it the CHO intake specifically, or just an increase in total Kcals that increases conversion to & production of serotonin?
Back in issue 141 Brock wrote:
Studies have shown that there’s often a direct association between obesity (due to overeating) and decreased brain serotonin levels. Without adequate levels of serotonin, the brain perceives that the body is starving and turns on the hunger mode. Obese people who suffer from low levels feel chemically compelled to eat more and more. Once they ingest carbohydrates and various sugars in general, they experience a temporary increase in serotonin levels.
So, do Carbs directly increase serotonin levels & how? Please respond with confidence or data - not arbitrary speculation, please