It has been shown that diets high in particular phytochemicals may have beneficial effects on mood. In particular, flavonoids have been shown to exert neuroprotective effects and may also affect neurochemistry. Grapefruit is a rich source of flavonoids of the flavananone subgroup and this may explain the mood elevating effects of grapefruit extracts. In one study the mood elevating effects of grapefruit juice extracts were assessed in rats. The grapefruit extracts were able to significantly decrease the depressive and anxious behaviour exhibited by the animals when exposed to experimental stress. The anxiolytic effects of the grapefruit juice extract was not as pronounced as that of the benzodiazepine drug diazepam, but the antidepressant effects of the grapefruit extract were comparable to the antidepressant drug imipramine. Flavonoids within grapefruit may exert their protective effects through interaction with the GABAA receptors in the brain, may decrease depressive symptoms through inhibition of monoamine oxidase enzymes.
However, another possible mechanism that may explain the mood elevating effects of grapefruit are the neuroprotection that may be conferred by phytochemical components of grapefruit extracts. For example, in one study peel extracts of grapefruit were prepared from the white and pink peels of grapefruits. These grapefruit extracts were shown to possess significant antioxidant capacity. When the grapefruit peel was analysed for antioxidant phytochemicals, 13 flavonoids were identified including naringenin, isonaringenin, hesperidin, neohesperidin, naringin, hesperetin, isosinensetin, nobiletin and tangeretin. Naringenin and isonaringenin were the main flavonoids in all peel extracts. The presence of these flavonoids likely explains in part the antioxidant effects of the peel extracts. Further, the peel extracts were shown to exert significant neuroprotective effects on neuronal cells grown in culture, something which may also be due to the high flavonoid content of the grapefruit peel extracts.
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