Is junk food to blame for the obesity epidemic?

Fast food, soft drinks and candy are often painted as the driving forces behind America's obesity epidemic, but new research suggests there's more to it than that.

In fact, according to the study from the Cornell University Food and Brand Lab, junk food does not appear to be a leading cause of obesity in the United States. Rather, the researchers suggest that the blame lies with Americans' overall eating habits -- particularly the amount of food consumed.

But the researchers emphasize that the findings do not give people a free pass to indulge in junk food.

"If you over-eat junk foods, they are going to make you fat," study author David Just, PhD, co-director of the Cornell University Food and Brand Lab, told CBS News. "It's just that it doesn't look like that it's those foods that are making people fat generally. It's something else. It's their broader diet or it's their exercise regimen."

Just worked with lab co-director Brian Wansink, PhD, to review the 2007-2008 Centers for Disease Control and Prevention's National Household and Nutrition Examination Survey -- a nationally representative sample of approximately 5,000 adults in the U.S.

The participants were asked to recall their food intake within the last 24-hour period on two separate occasions. Height and weight were also collected to calculate body mass index (BMI).

The Cornell team's analysis, published in the journal Obesity Science & Practice, showed something surprising: there was no significant difference in junk food intake between overweight and healthy individuals. In fact, consumption of soda, candy and fast food was not linked to BMI for 95 percent of the population. The exception came with those on the extreme ends of the BMI spectrum: the chronically underweight and the morbidly obese.

While the researchers emphasized that eating junk food is still certainly unhealthy, they concluded that the overwhelming majority of weight problems are not caused by consumption of soda, candy and fast food alone. Rather the problem is that many Americans are just eating too much and not exercising enough.

For example, the researchers note that the average daily calories consumed in the U.S. in the 1970's, before the obesity epidemic took off, was 2,039 -- compared to the average of 2,544 consumed circa 2010.

The results, the researchers say, have big implications for how we think about food and weight gain.

"If you're thinking about this as a dieter, more than likely if all you're doing is cutting out junk foods it's not going to have much of an impact," Just said. "More importantly, if you're thinking about this in terms of food policy and how to encourage people to have healthier diets and be a healthy weight, targeting narrowly these foods probably isn't going to do it. It's more complicated than that. It's our entire diet."

But experts caution that the study should not be interpreted to mean that eating junk food is not harmful to weight.

"I don't think we can say that fast food, candy and soda are completely unrelated to body weight," Alissa Rumsey, a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics, told CBS News. "These items are generally very high in calories and very low in nutrients. They are also heavily processed, and contain a lot of added fat and sugar."

Rumsey also pointed out that junk food is low in protein and fiber, doing little to keep you full and making it easy to over-consume calories.

"I find that when people cut down on these foods, and add whole, real foods like fruits, vegetables, lean protein and healthy fat, they lower their calorie consumption naturally without feeling hungry or deprived," she said. "While it is OK to treat yourself once in awhile, these types of junk foods should not be part of your daily diet."

This week, the Food and Brand Lab also released another study looking at the connection between what's eaten for breakfast and a healthy weight. After surveying almost 150 healthy-weight people, the researchers found that the most common breakfast items they consumed were fruits, dairy, cold cereal/granola, bread, eggs, hot cereal and coffee.

Though egg consumption was higher than expected, the researchers said that much can be learned from the breakfast habits of healthy-weight people.

"One important take away from this study is that a very high rate of slim people actually eat breakfast instead of skipping, which is consistent with previous research on the importance of breakfast," lead author Anna-Leena Vuorinen said in a statement. "But what stands out is that they not only ate breakfast, but that they ate healthful foods like fruits and vegetables."