According to a recent report in The Washington Post , the average American woman now weighs as much as the average 1960’s man. The average man isn’t doing any better—having gained nearly 30 pounds since the 1960’s to an average of 195.5 pounds today.

The obesity epidemic has many pointing fingers at the Western lifestyle. A concoction of calorie packed, high fat, high sugar processed foods combined with increasingly sedentary habits, the Western lifestyle seems a sure recipe for obesity.

Yet there is more to this epidemic than a change in lifestyle. Some studies suggest that our susceptible to obesity may be, at least partly, based on our genes. That may be why one person can eat three layer chocolate cake and stay thin, while another may see it land directly in his waistline.

Genetic Roulette

Based on studies using identical and fraternal twins that share in the same gene pool, an estimated 40-70% of the variation in body mass index , a common way of measuring obesity, may be due to genetic factors. That makes obesity one of the most genetically influenced traits we inherit.

Our genes are more likely to influence our appetite than how many calories we burn. In addition to total body weight, our genes influence total body fat and the distribution of our body fat— determining whether it lands as belly fat or in other locations. Even our food preferences are partly genetically determined.

So far, from studying the human genome, about 75 genetic variants have been linked to common obesity. Each one has a subtle effect on weight. However, even when taken together, these genetic variants only account for approximately two to four percent  of the estimated 40-70% variability in body weight that is attributable to genetics.

Why do these variants not explain the degree to which obesity is heritable? Scientists speculate the reasons may be that there are gene variants that we haven’t yet identified, that genes are modified after we inherit them (a process called epigenetic change) or most significantly, that it’s how our genes interact with our environment that determines how they are ultimately expressed.

Genes + environment = obesity

The genetics behind obesity mean that how you respond to a Western diet may be different than how I respond. The amount of weight we gain for any given amount of high fat, high sugar foods we eat and the amount of energy we expend for the same amount of exercise may be different. However, while genetics may explain part of the obesity epidemic, scientists still estimate genetics account for a very small percentage of obesity.

In the future, as we identify more “fat genes,” we may be able to design drugs that target these genes and treat obesity.

The bottom line is that even though how we respond to a particular diet may be different, the choice of whether we eat high fat, high sugar foods and exercise is still ours. And with hard work, each of us can successfully control our weight.

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