It’s raising interesting questions about whether a shift in public health policies helps explain what’s happening.

First lady Michelle Obama has become the face of the administration’s anti-obesity campaign, encouraging young people especially to eat better, move more, slim down. Now the Centers for Disease Control is reporting some progress.

Among preschoolers aged 2 to 5, obesity rates have dropped from 14 percent to about 8 percent overall during the past decade. It’s welcome news, since overweight preschoolers are five times as likely to become overweight adults.

Possible causes for the drop include efforts to promote breast-feeding, cut consumption of sugary drinks and encourage exercise. The first lady’s Let’s Move campaign, for instance, has focused on changing nutrition and exercise habits among children, planting and harvesting a White House vegetable garden, and collaborating with celebrities like comedian Will Ferrell.

WILL FERRELL:Also, is diet cola, is that a vegetable?

GWEN IFILL:And, yesterday, the administration unveiled new rules that ban marketing of unhealthy food in schools.

MICHELLE OBAMA:So, I think we can all agree that our classrooms should be healthy places where kids are not bombarded with ads for junk food.

GWEN IFILL:Former New York City Mayor Michael Bloomberg also took up the cause, moving to eliminate trans fats and limit the size of sodas and other sugary drinks.

Still, the CDC reports, the apparent progress among preschoolers does not extend to other age groups. Instead, a third of American children and teenagers and more than two-thirds of adults remain obese or overweight.

Christina Economos of Tufts University watches all this closely. She’s an associate professor at the Schools of Medicine and Nutrition Science. She also helps lead an initiative called ChildObesity180.org — got that right.

OK, Christina Economos, give me a sense of how significant the news of this decline is.

CHRISTINA ECONOMOS, Tufts University School of Medicine:Good evening.

These results are unequivocally amazing, and we really need to applaud, but we can’t stop yet. This is a small snapshot, and it’s a small group of children within the United States. And we need to reach all children between the ages of 2 and 19 and see progress.

GWEN IFILL: All good news is good news. I don’t disagree with you there.

But we do wonder whether — why it is younger people are seeing improvement and others are not.

CHRISTINA ECONOMOS:Well, in that age group, there’s been tremendous effort to regulate within child care centers, so that children are eating healthier foods, moving more and are exposed to less screen time.

We also know there have been changes to the WIC package over the last few years that provides more fruits and vegetables, whole grains and supports breast-feeding. And these efforts really target 2- to 5-year-old children and have resulted in really significant declines.

GWEN IFILL: Can I walk you through each of those possible reasons one at a time?

Let’s talk about the impact of sugary drinks. How much does that contribute to what we’re seeing? Especially in children so young, you wouldn’t think that would be a big issue.

CHRISTINA ECONOMOS:Sure.

A big percentage of sugar consumption in children comes from sugar-sweetened beverage. And there have been several public health campaigns in place over the last five to 10 years trying to reduce consumption for all children, particularly young children, so they don’t begin to drink sugary beverages and they continue consumption through the teen years.

We know that hundreds of calories are consumed by teenagers every year, and, surprisingly, even around 100 calories in our very youngest children.

GWEN IFILL:And what about physical activity? In this children this young, you would think that would be a given.

CHRISTINA ECONOMOS:You would think so. They should be getting between one to two hours per day.

But with all the different sedentary enticements now, children are often watching screens for many, many hours per day. And in unsafe neighborhoods, they might not be going outside to play. So a real effort is under way to get kids up and moving, expending calories for one to two hours per day. Within child care centers, that’s a really important cause.

GWEN IFILL:A lot of this is — in fact, we talked about recess coming — making a comeback on this program not long ago. In a lot of cases, we’re talking about nutritional awareness. Is this something which starts with adults and is affecting the youngest children?

CHRISTINA ECONOMOS: Definitely. I think there is an increased awareness in this country that we have an obesity epidemic, that we need to change our eating habits.

And, very importantly, we need to change the environment that we live in. So that means better policies, access and availability to healthier food for all Americans, so in underserved areas, as well as privileged areas. And many efforts are under way to make that happen.

GWEN IFILL:Is there any way to — you mentioned the difference between what’s happening in underserved areas, as well as privileged areas. And you also mentioned the change in the Women, Infants and Children nutrition program.

How much of that can you break out? I know this is a small incident, but how much do you know in these kinds of programs is it having an effect?

CHRISTINA ECONOMOS: Sure.

Well, we know that children who are eligible for supplemental food assistance like WIC are underserved children. And those changes are very important for them. But if we pull apart the recent data that we’re talking about now in the decline in the obesity rates, it starts to unravel when you look at the disparities.

So we know that white children have lower rates than black children and Hispanic children. And the disparities are quite striking. And that tells us that more effort has to be put into reaching underserved children, whether it’s income or race, ethnicity that’s impacting that, and putting more effort into government programs and community programs that really reach those children.

GWEN IFILL: How do you do that at a time of other priorities being made in government spending and in government in general and in nutrition programs? I mean, how do you take the piece of good news that we discovered today and have it extend to other demographics and age groups?

CHRISTINA ECONOMOS: Sure.

Well, this problem of obesity is quite complex, and it really requires a systems approach to deal with it. So it means that we can’t just work within health care or schools or child care. We need to work systematically and make changes in all of those systems, because collectively that’s what will show us the change.

And we know that children move out of environments throughout the day that are serviced by government dollars and private dollars. And so everyone working together and make these changes will really add up to declines in obesity throughout childhood.

GWEN IFILL:The other thing we heard about this weekend, we keep hearing about labeling and nutrition labeling, and also this idea that marketing in schools, even if you are not serving soda, just having a big soft drink sign could have an effect. How much of that is going to drive what happens next?

CHRISTINA ECONOMOS: I think it will be a big part. A lot of us believe that we need to reduce exposure to marketing for young children.

They’re unable to differentiate something that is being advertised to them and something that is being brought to them as education. So we need to work really hard to make sure that children aren’t exposed to messages for unhealthy foods, and schools shouldn’t be a place where they see those messages.

We also need to reduce exposure through television and other areas where they go.

GWEN IFILL:What do you say to people who look at something like this and say, the government cannot take away my hot dog for my child; this is just getting in the way of our right to nourish ourselves the way we choose?

CHRISTINA ECONOMOS:Yes, government steps in to make changes that we know are best for the population.

And we have done this through multiple public health strategies, with smoking, for example. And, in this case, we have a set of dietary guidelines. We know what children should be exposed to and should be consuming. And in situations where they’re spending large amounts of time, they should be provided with those healthy foods.

And if government plays a role, I think that’s really important. But it’s not just government. It’s also the private sector and academics who are doing good research, putting out recommendations, and communities across the country. So it really is a collective effort that we need to be focused on.

GWEN IFILL:Christina Economos of Tufts University, thank you very much.

CHRISTINA ECONOMOS: Thank you.