Adherence, Compliance, and Diet Quality Among Popular Diet Followers

1. To compare diet quality of vegan, vegetarian, paleo, and whole-food plant-based (WFPB) diets; 2. To examine how adherence varies by diet and relates to quality and diet duration; 3. To examine how compliance varies by diet and relates to quality, adherence, and duration. Analysis was conducted on a subsample of ADAPT participants (n = 1392) who completed a demographics and food frequency questionnaire (FFQ; DHQ-II). After excluding implausible energy intake (600 ≤ KCAL < 5,000), the final sample was 1291 (vegan [n = 355]; vegetarian [n = 90]; WFPB [n = 710]; paleo [n = 136]). Diet quality was measured with HEI and AHEI. Duration was categorized as short [<2 years (n = 501)]; moderate [2 to <7 y (n = 200)]; and long-term [7–10 + y (n = 592)]. A self-report adherence score was derived from questions targeting commitment to diet, ranging from 0–32. Compliance score for each diet was derived from reported intakes and DHQ-II (i.e., diet-specific restrictions), and data were %-based standardized. Models were adjusted for age and sex; select models were adjusted for diet duration. Mean (SD) HEI score was high in all plant-based diets, highest for WFPB 76.7(5.8), vegan 75.7 (6.5), vegetarian 72.6 (9.2), compared to paleo 62.5 (8.5); and with a similar ranking for AHEI. Vegans had highest mean adherence 23.5 (2.8) and paleos the lowest 20.0 (3.3). Vegetarians had highest mean compliance 71% (9) and WFPB lowest 53% (10). Compliance was positively associated with HEI score for WFPB and vegan with one percentage point of compliance associated with a 6.4-point increase in HEI for WFPB (SE ± 2, p < .004) and 17.1 for vegan (SE ± 4, p < .0001). For every point increase in compliance, adherence improved (5.4 ± 0.8, p < .0001) in the full sample, and by diet group. Diet duration was significantly associated with adherence in all but vegetarian. No relationship was observed between duration and compliance within diet. WFPB and vegan diets had the highest diet quality; all four had higher mean HEI than reported average in US adults (HEI = 59). Findings suggest that even imperfect compliance to plant-based diets is associated with greater diet quality. Diet adherence is a complex component of eating behavior, however reported adherence appears to predict higher compliance and longer maintenance. USDA Cooperative Agreements; NIFA National Needs Fellowship.