Carbohydrates are an important source of energy. But if you eat too many carbs, it can lead to health problems like obesity . That issue is the focus of this week's Weight of the Nation Conference.

A new report was released at the meeting. It estimates that by the year 2030, 42 percent of the U.S. population will be obese. That's 30 million more Americans than right now. The medical costs associated with that increase would total up to nearly $550 billion.

Soledad O'Brien talked with CNN's Dr. Sanjay Gupta about some of the reasons behind this issue.

Sanjay, before we get to the numbers, explain to me why are we getting that fat so quickly?

Well, you know, if there's any good news in this -- and I'm not sure there's a lot, Soledad, is that the numbers are actually originally expected to be worse. They said 51 percent at one time they predicted the nation would be obese. This is adults by the year 2030. So 42 percent is still nothing great, obviously. Eleven percent they think will be severely obese.

Look, Soledad, you'll hear a lot of the same sort of things that you've heard for some time. I mean, you've been covering this for a long time now, as have I. Too many fast food restaurants. It's too inexpensive to get unhealthy calories. There's not enough parks, too many roads, all those things, those keep coming up.

And despite the fact that those messages have been heard and understood, the problem just keeps getting worse. I think, you know, there's a lot to it at the individual level I think simple things can help, you know, simply eating more food in the morning, they find. Getting up and walking around.

But I think there's a larger problem, and that is that it's not just how much we eat but what we're eating as well. You know, sugar, for example, I'll just give you a quick example, probably behaves differently in the body than just about any other calorie. It makes you gain weight, but it also creates these lipids that are really bad for the heart, raises insulin levels and makes you store even more fat.

So for a long time, we thought health foods, for example, were low- fat, high-sugar foods. And as we became that country that ate that kind of diet, the problem just became even worse.

All right. Now you heard Dr. Gupta talk about some ways that individuals can work to prevent obesity. At the Weight of the Nation Conference, experts had some other ideas, some other solutions .

Some of those include a shirt in farming policies so there's more focus on fruits and vegetables. There's also a suggestion for a possible tax on sugary drinks, though there's some controversy associated with that. Another idea is to start the fight against obesity at school. For instance, requiring schools to provide an hour of physical education or activity every day.

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