Background  Both domestic and foreign studies on the diet quality of patients with thyroid nodules are rare at present, and the relationship between thyroid nodules and diet quality is still unclear.

Objective  This study aims to evaluate the diet quality of thyroid nodules with the China Healthy Diet Index (CHDI) and to explore the relationship between diet quality and thyroid nodules.

Methods  We conducted a hospital-based case-control study in which 387 patients with thyroid nodules were matched individually (1∶1) by gender and age (±3 years) to the controls who ordered a routine physical examine and with negative thyroid nodules reported by B-ultrasound in the same hospital. A structured questionnaire was applied to collect data on general characteristics and diet. CHDI was employed to evaluate the diet quality of the two groups. CHDI is based on the Dietary Guidelines for Chinese Residents and the recommended food intake in the balanced diet pagoda, combined with the dietary nutritional status of Chinese population. The index contains 13 scoring components, and the highest total score is 100, with a higher score representing better dietary quality. CHDI scores < 60, 60-<80, and ≥80 are recognized as unqualified, qualified, and good diet quality, respectively.

Results  The scores of the thyroid nodule cases were lower than the scores of the controls in total vegetables, dark vegetables, fruits, and fish/shrimps (all Ps<0.05). The nonparametric test results found that there were significant differences in the distributions of scores in total vegetables, dark vegetables, fruits, soybeans, and fish/shrimps between the case and the control groups (allPs<0.05). The percentages reaching the full scores in food variety, meat and eggs, and empty calories in both groups exceeded 60%, while the percentages reaching the full scores in whole grains/beans/tubers, dairy, soybeans, and sodium were lower than 30% in the two groups. The median CHDI scores of the thyroid nodule cases and the controls were 69.1 and 72.9, respectively; the cases' CHDI score was lower than the controls' (P<0.05). The proportions of unqualified diet in the case and the control groups accounted for 23.0% and 13.7% respectively (P=0.001). After being adjusted for education level, marital status, occupation, monthly household income per capita, body mass index, hypertension/diabetes, energy, and iodine intake, the results of logistic regression analysis showed that the risk for thyroid nodules was negatively associated with CHDI score (CHDI qualified group vs. CHDI unqualified group, OR=0.484, 95%CI: 0.291-0.804; CHDI good dietary quality group vs. CHDI unqualified group, OR=0.414, 95%CI: 0.230−0.746).

Conclusion  The diet quality of patients with thyroid nodules is lower than that of the control group, as the former reported lower consumptions of total vegetables, dark vegetables, fruits, and fish/shrimps. Those who have good or qualified diet quality show a reduced risk of thyroid nodules than those with unqualified dietary quality.