Diet quality in Japanese women with underweight: comparison with those with normal weight

Underweight is a serious health problem, particularly for women, because it increases the risk of osteoporosis, type 2 diabetes and low-birthweight infants. Evaluation of diet quality is important to understand whether dietary patterns differ in underweight women. This cross-sectional study assessed diet quality in Japanese women with underweight compared with those with normal weight. Data from 2977 Japanese women aged 20-79 years who participated in a nationwide online survey were analysed. Participants were categorised into underweight (BMI < 18·5 kg/m²) and normal-weight groups (BMI ≥ 18·5 to < 25 kg/m²), using self-reported weight and height. Dietary information was collected using a short version of the Meal-based Diet History Questionnaire. Diet quality was evaluated using the Healthy Eating Index 2015 (HEI-2015). Among the 2977 women analysed, 637 (21·4 %) were classified as underweight, while 2340 (78·6 %) were classified as normal weight. Participants in nutrition- and health-related occupations accounted for 41·7 % of participants. The mean total HEI-2015 score was similar between the underweight group (51·3) and the normal-weight group (51·5) (P = 0·33). Among the component scores, only the mean score for total protein foods was significantly (P = 0·02) lower in the underweight group than in the normal-weight group. The underweight group showed lower intakes of fish and shellfish and meat, but higher intakes of bread, pulses and nuts (all P < 0·05). In conclusion, overall diet quality assessed by the HEI-2015 was similar between underweight and normal-weight Japanese women.