We propose a parallel arm randomized clinical trial of two diets—a low carbohydrate ketogenic diet (LCKD) and a low fat diet (LFD). Following screening, eligible participants will undergo a six week dietary intervention that will include 7 clinic visits at the Duke Lifestyle Medicine Clinic (Director: Dr. Westman). In addition to the dietary intervention, participants will undergo fMRI scanning on two occasions: once in the week prior to randomization to a diet (Baseline Scan) and after three weeks of following a diet (Post-Diet Scan). During scanning participants will view food cues in order to assess the effects of diet on brain responses to different macronutrient content categories (e.g., High vs. Low Complex Carbohydrate). In addition to scanning measures, we will also record information regarding dietary intake, food preferences, weight, mood, and diet adherence.