Background Preliminary evidence suggests that a ketogenic diet may be effective for bipolar disorder. Aims To assess the impact of a ketogenic diet in bipolar disorder on clinical, metabolic and magnetic resonance spectroscopy outcomes. Method Euthymic individuals with bipolar disorder (N = 27) were recruited to a 6- to 8-week single-arm open pilot study of a modified ketogenic diet. Clinical, metabolic and MRS measures were assessed before and after the intervention. Results Of 27 recruited participants, 26 began and 20 completed the ketogenic diet. For participants completing the intervention, mean body weight fell by 4.2 kg (P < 0.001), mean body mass index fell by 1.5 kg/m2 (P < 0.001) and mean systolic blood pressure fell by 7.4 mmHg (P < 0.041). The euthymic participants had average baseline and follow-up assessments consistent with them being in the euthymic range with no statistically significant changes in Affective Lability Scale-18, Beck Depression Inventory and Young Mania Rating Scale. In participants providing reliable daily ecological momentary assessment data (n = 14), there was a positive correlation between daily ketone levels and self-rated mood (r = 0.21, P < 0.001) and energy (r = 0.19 P < 0.001), and an inverse correlation between ketone levels and both impulsivity (r = −0.30, P < 0.001) and anxiety (r = −0.19, P < 0.001). From the MRS measurements, brain glutamate plus glutamine concentration decreased by 11.6% in the anterior cingulate cortex (P = 0.025) and fell by 13.6% in the posterior cingulate cortex (P = <0.001). Conclusions These findings suggest that a ketogenic diet may be clinically useful in bipolar disorder, for both mental health and metabolic outcomes. Replication and randomised controlled trials are now warranted.
