In the year 2000, women ate the equivalent of one more large chocolate chip cookie every day - 335 more calories - compared to what they ate in 1971.
Men ate 168 more calories - slightly more than a 12-ounce Pepsi - each day, according to the study released Thursday by the Centers for Disease Control and Prevention.
Elisa Zied, a registered dietician for the New York State Dietetic Association, tells The Early Show co-anchor Rene Syler, "People are just consuming more calories. And that's, I think, largely in response to the whole fat-free craze that's been going on. People thought that gave them a license to overindulge. People went to foods perhaps that they didn't eat before, like potato chips and cookies that contain no fat, and didn't pay attention to portion size."
Jacqueline Wright, a CDC epidemiologist and study author said, "The majority of the increase in calories is from an increase in carbohydrate intake."
And she doesn't mean fruits and vegetables. It's the cookies, bagels, chips, pasta and soda that are to blame.
"People are gearing more away from whole grains, fruits and vegetables because they think that carbs are the enemy. But you need to eat those because they give you fiber, keep your heart healthy," says Zied. "And they are going to help you keep off weight. So you really need to include those things. But you do need to limit refined carbohydrates. Those will give you empty calories."
The extra calories are leading to extra pounds and chronic health problems. Obesity rates jumped from 14.5 percent of U.S. adults in 1971 to 30.9 percent in 2000, said Wright.
The average intake for men grew from 2,450 calories in 1971 to 2,618 calories in 2000. For women, caloric intake grew from 1,542 calories to 1,877 calories during the same time period.
The government recommends about 1,600 daily calories for women and 2,200 for men, and more for active people.
"We really need to start cutting portion sizes. We really need to start reading labels and paying attention to calories," says Zied. "And we need to incorporate the foods that keep us full: whole grains, fruits and vegetables, low fat dairy, lean meats, nuts, beans."
CDC officials did not say whether the study would affect the USDA's Food Pyramid, which recommends eating a diet heavy in breads and grains, which are high in carbohydrates. Wright said a federal panel examining general dietary guidelines will review the results of the study.
Zied notes, "I think the Food Pyramid is going to change over time. But I'm hoping it changes more in the direction of emphasizing again the fiber rich choices as opposed to things that don't contain a lot of fiber like cookies and crackers. So I think that they may start recommending fewer carbs, but I hope that that's not the case because again, people need that for energy -- the main source of fuel for your body. But you need to limit the extras in the refined sources."
The idea that carbohydrates lead to a bigger waistline was long espoused by the late Dr. Robert Atkins, whose low-carb diet has been followed by millions of people.
On the Atkins diet, up to two-thirds of calories may come from fat - more than double the usual recommendation - and violating long-held government guidelines and most nutritionists' advice.
CDC officials said people should watch their overall eating and exercise habits, not just carbs. Previous federal studies have blamed eating out and larger food portions.
"Certainly if our calorie intake is increasing and our physical activities really aren't changing too much, then we're going to be seeing weight gain," Wright said.
The CDC remains concerned that Americans still eat too much saturated fat, a risk factor for heart attacks and strokes.
The agency did offer a bit of hope in a separate study that indicates more Americans are making an effort to exercise. Only 25 percent of U.S. adults surveyed in 35 states and the District of Columbia said they did not exercise during their free time in 2002 -- down from 30 percent 15 years ago.
The federal agency's goal is to get that inactivity level down to 20 percent or lower, said Sandra Ham, a CDC health statistician.
"Physical activity levels have been improving," Ham said. "But there's still much more work to be done."