Diet quality indices are essential tools for assessing diet in epidemiological studies. However, established indices may not adequately capture features of current dietary patterns that impact health. Dietary diversity is widely recognised as an important indicator of diet quality(1). This study aimed to 1) develop a diet quality index that reflects modern dietary habits, and 2) evaluate its association with dietary diversity, compared to the Healthy Eating Index (HEI).

The ZOE diet score evaluates diet quality based on six components: macronutrient distribution (% total energy of protein, carbohydrates and fats), fibre intake (g/d), intake of poor quality fats (% total energy), plant diversity (counts/d), intake of ultra-processed foods (% total energy), and a personalised food score(2) (daily mean; range 0–100). Components were combined into a composite score ranging from 0 to 100 (higher scores indicating better quality). Dietary diversity was analysed from habitual diet (PREDICT food frequency questionnaire), calculated using Shannon’s Index. Longitudinal data (baseline and 4-months) from the ZOE PREDICT 3 study(2), in which participants took part in a personalised dietary program (PDP; n = 10,411; NCT04735835), were used to explore associations between the ZOE diet score, HEI, and dietary diversity using Pearson’s correlation. Strength of correlation was interpreted as weak (r < 0.3), moderate (0.3 ≥ r < 0.5) or strong (0.5 ≥ r ≤ 1.0).

Participants were 79.0% female (n = 8,224), had a mean age of 57.7 y (SD 11.1) and Body Mass Index of 26.3 kg/m2 (SD 5.5). At baseline, the mean ZOE diet score was 62.8 (SD, 9.4; range 21.1-87.7), and HEI was 77.9 (SD, 7.7; range 37.1-98.2). There was a stronger positive correlation between the ZOE diet score and dietary diversity (Pearson’s r = 0.39, p < 0.001), compared to the HEI and dietary diversity (Pearson’s r = 0.21, p < 0.001). After 4 months on a PDP, the mean ZOE diet score was 72.7 (change, 9.9; SD, 9.2; range 9.2-91.5), and HEI was 81.0 (change, 3.1; SD, 6.31; range 53.0–98.3). The PDP resulted in an increase in dietary diversity (mean change in Shannon’s index, 0.07; SD 0.25). There was a moderate positive correlation between the change in ZOE diet score and change in dietary diversity (Pearson’s r = 0.30, p < 0.001), while the HEI showed a weaker positive correlation with dietary diversity (Pearson’s r = 0.23, p < 0.001).

The ZOE diet score, incorporating dietary components relevant to current dietary habits and health, is positively associated with dietary diversity. The ZOE diet score is a valuable tool for capturing changes in diet diversity, as a component of overall diet quality, over time. Further research is needed to explore its potential in predicting long-term health outcomes.