What a shocker: Potato chips are the main culprit behind the average American’s small but steady yearly weight gain, according to a study at Harvard University.

But it’s not so much the chips’ fault as it is our inability to — paraphrasing the slogan of one of the best-known brands — eat just one.

After eating the final crumbs in a bag, carefully brush the residual salt and chip fragments off of your face and look around for somewhere to hide the bag from your significant other.

Of course, there’s nothing to joke about when it comes to obesity, and it’s a problem that is getting even bigger in the United States, pardon the pun.

Two-thirds of American adults are overweight or obese, according to researchers. Childhood obesity has tripled in the past three decades. Many of us remember the “freshman 15” of college. Now children are packing on those extra pounds before they’ve even left elementary school.

The study reveals little that we don’t already know. We need to eat more fresh fruits and vegetables, whole grains and nuts. We should cut back on potatoes, red meat, sweets and soda. And while exercise can help take off unwanted pounds, diet is key to avoid putting them on, Dr. Frank Hu, one of the Harvard study leaders, told the Associated Press.

The study is one of the largest of its kind. Doctors analyzed changes in diet and lifestyle habits of 120,877 people from three other long-running studies. For up to two decades, each had his or her weight measured every four years. All were of acceptable weight when the studies began. And here’s another surprise: All were health professionals.

While the delicious yet devilish chip was the biggest contributor to the increase in bulk (adding 1.69 pounds over the four years between weigh-ins), soda added a pound, one alcoholic drink a day put on 0.41 pound and potatoes other than chips added 1.28 pounds.

The study, funded by the National Institutes of Health and a foundation, also found that changing our lifestyle, even giving up bad habits, can be detrimental to our waistlines.

* Watching an hour of TV a day means a 0.31-pound increase.

* People who slept more or less than six to eight hours a night gained more weight.

* Quitting smoking translates to a five-pound weight gain. (Even with that, quitting smoking is probably the best favor you’ll ever do for yourself.)

The final words of wisdom from researchers echo the advice we’ve heard over the years: It’s not so much what you eat, it’s how much you eat, and it’s not so much what you eat and how much you eat, as how you prepare it.

That, and getting off the sofa –there’s nothing on now but reruns anyway — and taking a walk instead of reaching for the potato chip bag.

Another plus: You won’t have to follow the ant trail to find out where you hid all the empty ones.

Editorial by Bonnie Williams, Anderson (S.C.) Independent-Mail; distributed by Scripps Howard News Service.

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