Some people believe that if overweight or obesity runs in their family, they are destined to also be overweight or obese.  However, only half of a person’s body weight is due to genetics.  The remainder is due to lifestyle choices – foods consumed and physical activity level performed. 

Wardle J, et al. Evidence for a strong genetic influence on childhood adiposity despite the force of the obesogenic environment. American Journal of Clinical Nutrition, Vol. 87, No. 2, 398-404, February 2008

Formal genetic data based on twin, adoption, and family studies lead to the conclusion that at least 50% of the interindividual variance of the BMI is due to genetic factors. 

Hebebrand J, Hinney A. Environmental and genetic risk factors in obesity. Child Adolesc Psychiatr Clin N Am. 2009 Jan;18(1):83-94.