Relationship between 8-year weight change, body size, and health in a large cohort of adults in Thailand.

Background: Overweight and obesity have been shown to be risk factors for a range of non-communicable diseases, especially cardio-metabolic conditions, worldwide. But less is known about the effects of weight change on adults' overall health and wellbeing, particularly in transitional low- and middle-income countries. This study aimed to assess the relationship between 8-year weight change and measures of self-assessed health among Thai adults.

Methods: Data were collected from Thai adults aged 25-40 years (n = 27,003) enrolled in the Thai cohort Study and surveyed in 2005, 2009, and 2013. We used self-reported weight and height measurements at baseline and 2013, as well as three standard health questions regarding overall health, energy, and emotion asked at the two time points, to investigate the effects of weight change on health.

Results: Between 2005 and 2013, 6.0% of participants lost more than 5% of their baseline weight; 38.5% were stable (<5% loss to 5% gain); 23.0% slightly gained weight (>5%-10%); 22.8% gained moderate weight (>10%-20%); and 9.4% had heavy weight gain (>20%). Moderate (>10%-20%) and heavy weight gain (>20%) were both associated with an increased risk of reporting 'poor or very poor' overall health in 2013 among participants who had a normal body mass index (BMI) (adjusted odds ratio [AOR] 1.39; 95% confidence interval [CI], 1.13-1.71 and AOR 1.44; 95% CI, 1.09-1.90, respectively), were overweight (AOR 1.53; 955 CI, 1.01-2.29 and AOR 1.82; 95% CI, 1.04-3.19, respectively) or had obesity (AOR 2.47; 95% CI, 1.74-3.51 and AOR 3.20; 95% CI, 2.00-5.16, respectively) in 2005. Weight gain of over 20% also had a negative impact on energy level among cohort members with a normal BMI in 2005 (AOR 1.36; 95% CI, 1.11-1.65) and among participants with obesity in 2005 (AOR 1.93; 95% CI, 1.38-2.71). For those who were underweight, had a normal BMI, or had obesity at baseline, weight loss of more than 5% was associated with reporting emotional problems. Excessive weight gain adversely impacted participants who were underweight or had obesity at baseline.

Conclusion: Our study found that weight change, in particular weight gain, was associated with negative health outcomes, and this effect appeared to increase at higher levels of body size. The present findings may be useful to promote weight maintenance and healthy lifestyles.