Eating an orange a day may lower a person's depression risk by 20%, according to a study. That might be because citrus stimulates the growth of Faecalibacterium prausnitzii (F. prausnitzii), a type of bacteria found in the human gut, to influence production of the neurotransmitters serotonin and dopamine—two biological molecules known to elevate mood. We found that eating one medium orange a day may lower the risk of developing depression by about 20%. And the effect seems to be specific to citrus. When we look at people's total fruit or vegetable consumption, or at other individual fruits such as apples...