Underweight in Young Adult Women as a Dynamic Nutritional State: Evidence from Four Complementary Longitudinal
Katsumi Iizuka1, Hitomi Matsuura1,2, Kotone Yanagi3
1Department of Clinical Nutrition, School of Medicine, Fujita Health University, Toyoake 470-1192, Japan.
Nutrients
|April 14, 2026
Summary
Underweight in young Japanese women is a dynamic state, not a fixed condition. Different measurement methods yield varied results, highlighting the need for nuanced understanding of low body weight patterns.
Area of Science:
- Nutritional Science
- Public Health
- Biostatistics
Background:
- Underweight (BMI < 18.5 kg/m²), particularly among young Japanese women, lacks standardized measurement approaches.
- Prevalence of underweight necessitates a deeper understanding of its dynamic nature and measurement variability.
Purpose of the Study:
- To compare four analytical methods for assessing underweight in young Japanese women.
- To analyze the dynamic transitions and phenotypic classifications of underweight status over time.
Main Methods:
- Retrospective analysis of 883 underweight women (aged 20-29) over 6.1 ± 4.2 years.
- Comparison of year-to-year transitions, state occupancy, Aalen-Johansen estimator, and Kaplan-Meier Survival Analysis.
- Bidirectional flow analysis, BMI distribution, and time-weighted classification were employed.
Main Results:
- Significant discrepancies (31-point) were observed between methods (e.g., 78.1% vs. 47.1%).
- Bidirectional flow analysis revealed distinct inflow/outflow patterns across age groups (22-47 years).
- Time-weighted classification identified four phenotypes: persistent, moderate, intermittent, and transient underweight, with 35.2% exhibiting yo-yo patterns.
Conclusions:
- Underweight in young Japanese women is a heterogeneous, dynamic nutritional state, not a static condition.
- Methodological choices significantly impact underweight classification, underscoring the limitations of cross-sectional data.
- Phenotypic classification reveals distinct longitudinal patterns of low body weight, crucial for identifying at-risk subgroups.
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