Stigmatisation across the weight spectrum has been shown to negatively impact mental and physical wellbeing. ^{(Reference Marini1,Reference Brelet, Flaudias and Désert2,Reference Mensinger, Tylka and Calamari3)} While much attention has been given to anti-fat bias, anti-thin bias has remained largely unaddressed. A scoping review was conducted to assess the level of anti-thin bias in health and fitness professionals and examine the efficacy of interventions designed to minimize this. A comprehensive search was conducted during May and June 2022 across the Scopus, CINAHL, Medline and APA PsycInfo databases. Search terms were defined (including weight stigma and bias, thinness and underweight, fitness professionals and intervention studies), and articles published between 2012 to 2022 were examined using exclusion and inclusion criteria. 1426 search results were found and screened at the title, abstract and full text level. 99% of studies were excluded from the review as they had no mention of anti-thin bias. Seven studies were included in the final review and included cross-sectional, qualitative and longitudinal studies. Studies reviewed highlighted both individual and/or workplace factors that minimised weight bias towards fat and thin people. Tools used to measure implicit and explicit weight bias and stigma in participants were fairly consistent across studies; 43% (n = 3) used the Weight Implicit Association Test (IAP), 29% (n = 2) used the Anti-Fat Attitudes Questionnaire, and 14% (n = 1) used the Implicit Relational Assessment Procedure (IRAP). Most studies used multiple scales (including self-developed scales) and measures to collect data on other cognitive aspects such as vignettes measuring behavioural intention. While results were inclusive of data relating to anti-thin bias, there was an emphasis on anti-fat bias throughout the assessed studies. Though these studies acknowledged the existence of anti-thin bias with recommendations for interventions, no specific intervention studies were found to address this bias. This review demonstrates the discrepancies between anti-fat and anti-thin bias studies within existing literature, highlighting that anti-thin bias research is still very much in its infancy. Given the health and wellbeing implications of embracing body diversity, and the overall emphasis on anti-fat bias, there is a significant opportunity to explore interventions that target anti-thin bias and reduce health inequities on either side of the weight spectrum. Preliminary evidence to determine the extent of anti-thin bias must be established so that interventions can be developed to reduce its effects. Future research to determine the prevalence and drivers of anti-thin bias is warranted.