Entrepreneurship in stoma care nursing: difficulties experienced and strategies for overcoming them.

Obesity is one of the most pressing global public health challenges of the 21st century. Between 1 and 2.5 billion adults worldwide are classified as having overweight or obesity, and the prevalence is projected to rise further [, ]. Obesity contributes substantially to non‐communicable diseases (NCDs), including type 2 diabetes, cardiovascular diseases, and several cancers [], and imposes enormous health, economic, and social burdens now and in the future [, ]. Beyond the long‐term risks of high BMI, growing evidence indicates that fluctuations in BMI over time may independently pose health risks. Repeated cycles of weight gain and loss (‘weight cycling’) have been linked to adverse cardiometabolic outcomes, including type 2 diabetes, hypertension, cardiovascular disease, and higher overall mortality []. The physiological mechanisms are not fully understood, but weight instability may reflect or induce insulin resistance, elevated triglycerides, increased abdominal fat accumulation, or other metabolic disturbances, which in turn can increase cardiometabolic disease risk [, , , ]. Genetic influences on BMI have been shown in large‐scale twin [] and genome‐wide association studies (GWAS) [, ]. Twin and family studies also indicate that genetics contribute to weight changes in adulthood, with heritability estimates of 0.05–0.29 []. Prior research has reported phenotypic associations between BMI and subsequent weight change, as well as the genetic and environmental contributions to these associations []. However, studies on the heritability of BMI fluctuation, its links with BMI and BMI change, and genetic and environmental factors underlying these associations remain limited []. Although BMI fluctuations may largely be driven by environmental (i.e., neighbourhood walkability and the food environment) and lifestyle (i.e., changes in diet, physical activity) factors, or life circumstances, individuals may differ genetically in their sensitivity to such perturbations. If so, heritability of BMI fluctuation would reflect inherited differences in environmental responsiveness rather than direct genetic determination of weight fluctuation, consistent with the concept of ‘variability genes’ proposed by Berg []. To address this gap, we applied genetic twin modelling to pooled data from 14 longitudinal twin cohorts. BMI fluctuation was defined as variability around an individual's fitted BMI trajectory, and BMI change as linear increase or decrease over time. Our aims were to (i) assess cohort‐specific genetic and environmental effects and cross‐cohort heterogeneity for BMI fluctuation; (ii) examine how these effects vary across the adult life span; and (iii) identify genetic and environmental contributions to associations of BMI fluctuation with baseline BMI and BMI change across life stages.