It's plain biology: Eating carbohydrates (plentiful in pizza and cupcakes, but not so much in kale) boosts our levels of the feel - good hormone serotonin. (health.com)
Finally, any pleasurable activity should reduce stress by boosting levels of the happiness hormone serotonin. (supernaturalacnetreatment.com)
Important brain chemicals, including the mood - boosting hormone serotonin, are produced in the gut. (health.com)