IMPORTANCE: Presence of eating abnormalities is one of the core criteria for the diagnosis of behavioral variant frontotemporal dementia (bvFTD), yet their occurrence in other subtypes of frontotemporal dementia (FTD) and effect on metabolic health is not known. OBJECTIVE: To define and quantify patterns of eating behavior and energy, sugar, carbohydrate, protein, and fat intake, as well as indices of metabolic health in patients with bvFTD and semantic dementia (SD) compared with patients with Alzheimer disease (AD) and healthy control participants. DESIGN, SETTING, AND PARTICIPANTS: Prospective case-controlled study involving patient and caregiver completion of surveys. Seventy-five participants with dementia (21 with bvFTD, 26 with SD, and 28 with AD) and 18 age- and education-matched healthy controls were recruited from FRONTIER, the FTD research clinic at Neuroscience Research Australia in Sydney. MAIN OUTCOMES AND MEASURES: Caregivers of patients with FTD and AD completed validated questionnaires on appetite, eating behaviors, energy consumption, and dietary macronutrient composition. All participants completed surveys on hunger and satiety. Body mass index and weight measurements were prospectively collected. RESULTS: The bvFTD group had significant abnormalities in the domains of appetite (U = 111.0, z = 2.7, P = .007), eating habits (U = 69.5, z = 3.8, P = .001), food preferences (U = 57.0, z = 4.1, P = .001), swallowing (U = 109.0, z = 3.0, P = .003), and other oral behaviors (U = 141.0, z = 2.6, P = .009) compared with the AD group. The bvFTD and SD groups tended to have increased energy consumption. Compared with controls, the bvFTD group had significantly increased carbohydrate intake (251 vs 170 g/d; P = .05) and the SD group had significantly increased sugar intake (114 vs 76 g/d; P = .049). No significant differences in total fat or protein intake between the groups were found. Despite similar energy intake, the SD group had lower hunger and satiety scores compared with the bvFTD group. In contrast, hunger and satiety scores did not differ between the bvFTD group and controls. The abnormal eating behavior was found in the 2 groups (bvFTD and SD) with the highest body mass index (F = 4.2, P = .008) and waist circumference (F = 6.4, P = .001). CONCLUSIONS AND RELEVANCE: Abnormal eating behaviors are prominent in patients with bvFTD and those with SD and are not limited to increased appetite. The observed higher intake of sugar and carbohydrates was found in patients with the FTD subtypes and those with higher body mass index and waist circumference and was not explained simply by increased hunger or lower satiety.