Weight-loss diets are notorious for their low adherence, which is a barrier to efforts to reduce population rates of overweight and obesity. However, there is some evidence that adherence is better among people on other kinds of diets, such as vegan and gluten free. This study aimed to explore the predictors of dietary adherence across five restrictive dietary patterns (vegan, vegetarian, paleo, gluten free, and weight loss). This study used both qualitative and quantitative methods among 292 adult community members who were following a restrictive dietary pattern. Personality, mental health, and motivational predictors of adherence were examined. Substantial differences in adherence were found between dietary groups, with vegans and vegetarians being particularly high in adherence and gluten-free and weight-loss dieters being comparably low. Four consistent predictors of adherence across different dietary patterns were supported in both the quantitative and qualitative analyses. Self-efficacy and social identification with one's dietary group positively predicted adherence. Conversely, being motivated in one's dietary choices by mood or by weight control negatively predicted adherence. These findings speak to the importance of social and motivational factors in determining adherence. The results also illustrate the utility of looking beyond weight-loss dieters and virtuous individual traits for insights into how adherence may be improved.