Government proposals to revamp food-nutrition labels and regulate junk-food marketing in schools were accompanied last week by a rare glimpse of good news about the nation's weight woes: A new report showed a 43% drop in the obesity rate for 2-to-5-year-old children in the past decade.

The two new regulatory proposals won't take effect for a while. But they join other measures enacted in recent years by the government and the food industry through self-regulation to reduce the exposure of junk foods and the marketing of it to kids.

How much credit can the regulations take for the apparent improvement in obesity rates? The answer gets a little blurry.

The obesity findings, which were led by a Centers for Disease Control researcher and published in the Journal of the American Medical Association, found that just over 8% of children ages 2 to 5 were obese in 2011-2012, down from nearly 14% in 2003-2004. Despite that drop, however, the study found that obesity rates for the broader population remain unchanged, and rates for women over 60 increased.

Marlene Schwartz, director of the Yale Rudd Center for Food Policy & Obesity, said that industry self-regulation may not have had a huge impact on the overall drop in obesity among young kids, though it does likely reduce exposure to unhealthy brands.

She gave more credit to government-assisted food programs that promote healthy eating among infants and toddlers. She pointed to a 2009 overhaul of a federal supplemental nutrition program called Women, Infants & Children, or WIC.

The program targets low-income pregnant, breastfeeding, and non-breastfeeding postpartum women, as well as infants and children up to age five who are found to be at nutritional risk. It was altered in 2009, with the main changes being vouchers for fruits and vegetables, new whole-grain products, lower fat content of dairy foods and reduced juice quantities. WIC-authorized food stores were required to carry the foods that met the new criteria.

According to the U.S. Department of Agriculture, an average of 9 million people per month participated in the program in 2011.

Health experts have noted that the decrease in obesity rates indicate is that it's easier to prevent obesity from occurring in the first place, rather than reverse obesity in people already plagued by it.

"When you're looking at the same age group over time, you're not actually looking at the same kids," Ms. Schwartz said. "It's not that the kids who were obese before lost weight, it's that more kids that age didn't become overweight or obese," she said. "People have this idea that obese kids are going to be able to lose weight easily, but that's a more difficult change. It's easier to prevent kids from becoming overweight."

Elaine Kolish, director of the industry's Children's Food and Beverage Advertising Initiative, was careful not take too much credit for the obesity improvement. The group, which launched in 2007, oversees rules meant to shift the mix of advertising directed at children to healthier products. "It would be presumptuous of us to say our efforts led to [the obesity rate drop]," she said. "I think we are one piece of this very large environment, all working together to do the right thing."

Janet Helm, a registered dietitian and the chief food and nutrition strategist for PR agency Weber Shandwick, credited the the attention that First Lady Michelle Obama has given the issue, as well as increased media attention. "We are starting to see some benefit because the awareness of the obesity epidemic has never been higher," she said.

The First Lady was the public face of the two new proposals announced last week: The new school- marketing rules include the elimination of the advertising of sugary drinks and junk foods on vending machines and around campuses. The nutrition-labeling change, announced separately, would mandate several key changes to the 21-year-old Nutrition Fact panel on packaged foods, including putting calorie contents in larger, bolder type.

Other recent key food regulations include the impending chain-restaurant menu law that requires restaurants to list calorie counts. Ms. Schwartz said food and restaurant labeling laws typically have a bigger impact on college-educated white women than other demographics. She did note, though, that the requirement of food companies to list nutrition data in some cases has led the companies to reformulate foods.