Background: As dietary habits shift in response to environmental concerns and health awareness, understanding healthcare professionals’ perceptions of vegan diets is crucial. Objectives: This study aimed to identify the beliefs and attitudes of primary care doctors and nurses in Spain towards vegan diets. Methods: A questionnaire-based, observational, cross-sectional study was conducted among 208 healthcare professionals. Results: 87% of participants followed an omnivorous diet, while only 3.4% identified as lacto-ovo-vegetarian (LOV) or vegan. Statistically significant differences were observed by sex, with women more likely to agree that livestock farming contributes to global warming (27.3% and 28.0% vs. 17.0% and 12.8%, respectively; p = 0.02). Additionally, women were more inclined to consider vegan diets suitable for vulnerable groups, such as pregnant women and children, when adequately supplemented (24.8% and 17.4% vs. 10.6% and 10.6%, respectively; p = 0.030). Healthcare professionals who followed a LOV or vegan diet were more likely to disagree with the notion that vegan diets do not provide the necessary macronutrients and micronutrients compared to omnivores (strongly disagree 19.9%, 56.3%, 85.7%; p = 0.001 for omnivores, flexitarians, and LOVs/vegans, respectively). Conclusions: Current nutrition training may not meet the needs of doctors and nurses. Furthermore, it is implied that some professionals’ attitudes towards vegan diets may be more influenced by personal beliefs than by scientific literature. These findings can inform future clinical guidelines and support a more evidence-based approach to dietary counselling for vegan populations.