Additional Study Information: We are recruiting volunteers, aged 18-70, for a research study on the buildup of excessive liver fat ("fatty liver disease") in people with or at risk for type 2 diabetes because their bodies are resistant to the actions of the blood sugar-lowering hormone, insulin. To do this, we seek to temporarily induce or accentuate insulin resistance in 14 volunteers using a medication called alpelisib (brand name: Piqray), which is a drug (pill) used to treat certain breast cancers. We're looking for people with body mass indices (BMI) in the lean, overweight, or obese range (18.0-39.9 kg/m2) and do not have a diagnosis of diabetes, although prediabetes is okay for those in the overweight and obese ranges. Participants will stay overnight in the hospital twice, for up to 36 hours, 2-8 weeks apart. Participants will, in random order, take a single dose of either alpelisib at one of the visits and a single dose of placebo at the other. In both cases, they will then receive intravenous (into the vein) infusions of non-radioactive tracer molecules that allow us to measure how the liver is producing glucose (sugar) and certain fats. Eligible participants will receive compensation for their participation, including a stipend (salary) of up to $700 and reimbursement for travel expenses.