INTRODUCTIONObesity is a global pandemic and a major health concern. Obesity is a common but complex, multifactorial disorder with high heritability, where as much as 80% of the variance in the body mass index (BMI) is attributable to genetic factors.

MATERIALS AND METHODSLiterature on the contributing factors of the current obesity epidemic, and genetic basis of human obesity, were reviewed.

RESULTSThe current increasing prevalence of obesity is a relatively recent global event driven by our modern lifestyle and dietary habits. Common obesity is the result of subtle interaction between numerous related genetic variants and environmental factors. The role of the obesity genes in this current epidemic is passive, but its impact is highly significant, because individuals with these genes may be predisposed to severe or even morbid obesity when exposed to the modern "obesogenic" environment.

CONCLUSIONSThe human weight regulation mechanism evolved and becomes efficient in preventing weight loss, but is relatively ineffective in preventing excessive weight gain. The modern "obesogenic" environment encourages a sedentary lifestyle and provides easy access to processed food, which leads to a reduction of energy expenditure and increased caloric intake. We have inadvertently created a biology-environment mismatch, as the human weight regulation is unable to evolve fast enough to keep pace with the environmental change. This resulted in maladaptation of an otherwise sound and metabolically efficient physiological mechanism, with serious metabolic consequences.