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 to those with normal weight. Data from 2977 Japanese women aged 20–79 who participated in a nationwide online survey were analyzed. Participants were categorized into underweight (body mass index [BMI] <18.5 kg/m 2 ) 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. Among the 2977 women analyzed, 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 Healthy Eating Index 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 Healthy Eating Index 2015 was similar between underweight and normal weight Japanese women.