Child Bipolar Network Ketogenic Diet Approach to Bipolar Disorder in Adolescents

Inclusion Criteria: * Youth must be ages 12 to 21 years old and speak English * Youth must be appropriate for outpatient treatment (i.e., not a danger to self or others; not acutely psychotic, suicidal or manic; not in need of partial or full hospitalization) * Youth must have a current BSD (bipolar I, II per DSM-5 criteria (Association, 2013) or other specified BSD by the University of Pittsburgh diagnostic criteria (Birmaher et al., 2006). The Pittsburgh other specified BSD criteria require recurrent and distinct 1-3 day periods (minimum 4 hours/day) in which there has been abnormally elevated, expansive, or irritable mood plus two (three, if irritable mood only) symptoms of mania that caused a change in functioning and totaled at least 4 days in the child's lifetime * Active symptoms: In the 2 weeks prior to study intake, participants must have had weekly depression Psychiatric Status Ratings (PSRs) of 3 (moderate) or higher (using the 1-6 depression severity scales from the Adolescent Longitudinal Follow-up Evaluation, or A-LIFE); or an interview-based Children's Depression Rating Scale, Revised (CDRS-R) score covering the prior 2 weeks of \> 20. Youth may also enter with mixed symptoms (e.g., simultaneous elevations of \> 3 on the PSR depression and hypomania scales, with Young Mania Rating Scale scores of 12 or higher), without meeting criteria for a full manic episode in the past month. * Participants must continue to meet the study's active symptom criteria when beginning the phase II keto "ramp-up" phase: a depression PSR rating of 3 or higher over the prior 2 weeks, and a CDRS-R score covering the prior 2 weeks of \> 20. * Youth/parents must be willing to participate in evaluation and medication management sessions with a study psychiatrist and the study dietitian for assessment of the diet and side effects. * Youth under 18 years old must have at least one English-speaking parent or other caregiving family member consenting to participate in the study and available for consultation if needed * Youth and (for minors) all parents/legal guardians with health care decision making rights must express willingness to have the youth be in the study and try the keto therapy, assuming that the youth is eligible. The team must ascertain that the participating minor's youth/caregiver is likely to make a strong effort to adhere to the study's protocol. Exclusion Criteria: The youth must not have any of the following needs or conditions for which the keto diet may be contraindicated: * pregnancy or breastfeeding * underweight (BMI below 18.5) or wasting syndrome (e.g., anorexia cachexia) * current or history of anorexia nervosa * current disordered eating (bulimia or binge eating disorder) * autism spectrum disorder diagnosis level 2 or greater (more than mild) * cardiac issues, including history of arrhythmia, or cardiovascular or cerebrovascular disease * type I and type II diabetes * history of seizures/epilepsy * history of stroke or cancer * unstable respiratory condition * severe gastroesophageal reflux (GERD; painful/impairing despite prescription medication) * substance use disorder (with an exception for mild cannabis or nicotine use disorders) * history of kidney stones/disease * diseases involving the pancreas, liver, gallbladder or thyroid, including Von Gierke's glycogen storage disease * Condition with high cholesterol of triglycerides will prompt physician review of eligibility (LDL\>190 or triglycerides\>500) * genetic metabolic disorders: either porphyria (impacting the body's ability to make hemoglobin) or fatty acid oxidation disorder (FAOD) * rare conditions of defective ketone production or breakdown (carnitine deficiency, carnitine palmitoyl-transferase deficiency, carnitine-acylcarnitine translocase deficiency, mitochondrial fatty acid β-oxidation disorders, Succinyl-CoA:3-ketoacid CoA transferase deficiency (SCOT), or pyruvate carboxylase deficiency) * youth must not be taking SGLT-2 inhibitors (e.g., canagliflozin), insulin, or sulfonylureas (to avoid hypogycemia), or Antihypertensive medication (e.g., lisinopril/ACE Angiotensin inhibitors ending in "pril", ARB Angiotensin II receptor blockers, spironolactone/Aldactone, Thiazide-type diuretics)