Do Genes Make Us Fat?
But the precise affect of genes on weight and weight gain is hard to measure. For example, our eating habits and lifestyle (e.g. watching TV) are largely conditioned by family environment. So even though a child with two overweight parents is estimated to have a 70 percent chance of growing up obese, this may be due to family influence rather than genetic influence.
Lastly, whatever affect genes have on weight, they cannot explain the huge upsurge in general obesity over the past 35 years. This is due almost entirely to bad diet and an increasingly sedentary lifestyle.