Insistence on Sameness has been pathologized as a subtype of restricted, repetitive patterns of behavior, interests, or activities, in autism. We examined the meanings of Insistence on Sameness for autistic adults through the lens of critical autism studies and environmental psychology, exploring their foodways and experiences of food environments, in relation to eating out and grocery shopping, and their experiences of autism (self-)diagnosis. Data were collected from earlier individual email interviews with Brazilian adults on the autism spectrum (N = 16), either formally diagnosed in adulthood (n = 10) or self-diagnosed (n = 6). Our thematic analysis generated the following three themes: (1) Insistence on Sameness behaviors in food space as participants' "efforts for human-environment optimization"--reducing uncertainty, uncontrollability, and exposure to unwanted sensory stimuli and social interaction; (2) suppressed Insistence on Sameness behaviors for being considered "weird habits"; and (3) realization of Insistence on Sameness as "an authentically autistic way of coping" when self-knowledge deepens through autism (self-)diagnosis. Our findings suggest autistic adults' insistence on sameness is an authentically autistic way to appropriate space and exercise their right to comfortably co-exist and live as human beings and as themselves.