The average American will gain about a pound during the holidays, and soon it will be time for New Year’s resolutions to shed the pounds. Two-thirds of Americans are already overweight or obese, and the turkey and candies aren’t helping.

Who’s to blame for the obesity epidemic in America? Of course there’s no single answer. There are many things that contribute to Americans’ ever-expanding waistlines. All of them come down to nature and nurture, genetics, and environment.

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On the environment side, most people today get less exercise than they did decades ago. The labor force, which used to be dominated by physical activity such as farming and manufacturing, is now largely sedentary, chained to computers at desks. Less exercise means fewer calories spent each day and week, translating into excess weight over months and years.

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That wouldn’t be a problem if people were eating less, but in fact people are eating more than ever. For example, a 2004 Centers for Disease Control report found that American women eat over 300 more calories each day than they did in 1971. The idea that Americans are obsessed with weight loss is a myth: Fewer than one-third of Americans get regular exercise, and fewer than one-quarter are dieting at any given time.

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The 'Fat Gene'

On the genetics side, there’s an element of inherited predisposition toward (or increased risk factor for) obesity. Researchers have identified a “fat mass and obesity associated,” or FTO, gene that increases the likelihood that a given person with that gene will be obese by about 23 percent.

News about this so-called fat gene has given some overweight or obese individuals the idea that the dice are loaded and there’s little point in even trying to lose weight; dieting is difficult enough without our heredity fighting against us.

However, before you throw up your arms and blame your genes for your growing girth, there’s good news from a new study published in PLoS Medicine titled, “Physical Activity Attenuates the Influence of FTO Variants on Obesity Risk: A Meta-Analysis of 218,166 Adults and 19,268 Children.”

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The study found that the effect of the gene on weight gain is very small, only about 2 pounds. So, for example, if you carry the FTO gene and you’re 20 pounds overweight, at best you can blame about 2 of them on your parents; the other 18 pounds (about 90 percent of your extra weight) are the result of your dieting and exercise habits (or lack thereof).

The study also found that the “association of the FTO variant with BMI and with the odds of obesity was reduced by approximately 30 percent in physically active compared to inactive adults.” In other words, getting exercise (defined in this study rather generously as at least one hour of moderate to vigorous activity per week) reduces the effect of the “fat gene” by about a third.

As the study notes, the research “demonstrates that a genetic susceptibility to obesity is modifiable by lifestyle (choices).” This means that, far from the “fat gene” dooming its carriers to a life of obesity impervious to weight loss, overweight individuals have an enormous amount of control over their weight. We can’t control our genes, but we can control what we eat and how much exercise we get.

Do Diets Work?

The claim that "diets don't work" is often touted by people trying to sell a book or seminar with the secrets on their special pills or technique to help you lose weight. (Or, in the case of fat-acceptance activists, the claim is used to justify giving up and instead accepting your obesity.)

The fact is that most people can lose weight on just about any sensible diet. Often, merely beginning to pay attention to what you're eating is enough to reduce calorie consumption, since a lot of snacking behavior is subconscious — many people are unaware of how much they eat and how often.

Dieting is simply making healthy choices about the types and amounts of foods you consume. Dieting is not the same as a fad diet, nor is it a starvation diet. Doctors and researchers have known for decades that the best way to lose weight and keep it off is through diet and exercise.

It is true that most people who go on a diet do not remain on that diet for the long term. Some stop because they don't see results fast enough, but most simply give up. They lack the willpower and self-discipline to stick to the diet and end up going back to their old eating habits. The diet didn't fail; the dieter did.

The study’s authors hope that that their research will help fight “fat fatalism,” the idea that trying to lose weight is pointless: “Our findings … emphasize that exercise/physical activity is a particularly effective way of controlling body weight in individuals with a genetic predisposition towards obesity and thus contrast with the determinist view held by many that genetic influences are unmodifiable.”

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