Examining Neurobiological Mechanisms Underlying the Therapeutic Effect of the Ketogenic Diet in Bipolar Disorder (BD)

Inclusion Criteria: All participants: * 18-40 years of age * Not following a ketogenic diet BD hypomanic group (n=30): * Meeting sex proportion: 50% female * Meeting diagnosis proportion: 50:50% Bipolar I: Bipolar II (BDI:II) (Diagnostic and Statistical Manual of Mental Disorders 5; DSM-5) * Score greater than 10 on the Young Mania Rating Scale score(YMRS) * BD medications will be allowed as in our previous studies: any combination of atypical antipsychotics, lithium, antidepressants, anxiolytics (common in BD) BD euthymic group (n=30): * Meeting sex proportion: 50% female * Meeting diagnosis proportion: 50:50% BDI:II (DSM-5) * Score less than or equal to 10 on YMRS * BD medications will be allowed as in our previous studies: any combination of atypical antipsychotics, lithium, antidepressants, anxiolytics (common in BD) Healthy Control (HC) Group (n=30): * Sex matched with BD groups * No psychiatric history Exclusion Criteria: All participants: * Not between 18-40 years of age * History of head injury, neurological, pervasive developmental disorder (e.g. autism), systemic medical disease and treatment (medical records, participant report) * Mini-Mental State Examination score (cognitive state) \<24 * Premorbid National Adult Reading Test Intelligent Quotient (NAART IQ) estimate\<85 * Visual disturbance: \<20/40 Snellen visual acuity * History of alcohol/substance use disorder (SUD; all substances, including nicotine), and/or illicit substance use (except cannabis) over the last 6 months (SCID-5). Note: lifetime/present cannabis use (at non-abuse (\<3 times in the past month) and non SUD levels) will be allowed, given its common usage in BD and young adults. Cannabis SUD over the last 6 months will not be allowed. Urine tests on scan days will exclude current illicit substance use (except cannabis). Salivary alcohol tests on scan days will exclude intoxicated individuals * MRI exclusion: metallic objects, e.g., surgical implants; claustrophobia; positive pregnancy test for females or self-report pregnancy * Unable to understand English * Conditions related to the pancreas, liver, thyroid or gallbladder. * Taking anticoagulants and/or those with blood dyscrasias (illnesses) who have coagulation disorders (eg, hemophilia) because of the ketomojo finger stick blood tests * Scoring 3 or higher on positive symptom factor questions on the Positive and Negative Syndrome Scale (PANSS) questionnaire (indicative of psychotic symptoms) * Currently following a ketogenic diet * Head circumference larger than 24 inches (62cm) and/or chest circumference larger than 55 inches (139 cm) BD hypomanic group: * Must be meeting sex proportions: not 50% female * Must be meeting diagnosis proportions: not 50:50% BDI:II (DSM-5) * Diagnosis of BD in a manic or euthymic episode * Score 10 or lower on the Young Mania Rating Scale score(YMRS) * Using psychotropic medications other than those allowed in inclusion criteria * Does not have a smartphone with a) iOS version 12.0 or above, or b) Android version 8 and later to use with the Keto-Mojo app BD euthymic group: * Not meeting sex proportion: not 50% female * Not meeting diagnosis proportion: not 50:50% BDI:II * Diagnosis of BD in a depressive, hypomanic, or manic episode * Score greater than 10 on YMRS * Using psychotropic medications other than those allowed in inclusion criteria * Does not have a smartphone with a) iOS version 12.0 or above, or b) Android version 8 and later to use with the Keto-Mojo app Healthy Control (HC) Group * Not sex-matched with BD groups * Has psychiatric history