“It’s great to see companies selling fewer calories and reformulating their products to reduce fat and sugar, but it’s hard to know how much is due to the proactive efforts of the industry rather than changes in Americans’ eating habits, ” said Margo Wootan, director of nutrition policy at the Center for Science in the Public Interest. “It’s not as if Coke and Pepsi are encouraging people to drink less soda — in fact, Coke and Pepsi are lobbying against state and local policies aimed at reducing consumption of soda.”

Nonetheless, Ms. Wootan said a reduction of 78 calories a day was significant, whoever is responsible. “The whole obesity epidemic can be explained by an extra 100 to 150 calories a day,” she said.

Sales of the processed foods that typically line the long rows in the center of grocery stores have been stagnant, and beverage companies have been scrambling as consumers abandon sugary carbonated drinks for water and diet varieties.

“I see an evolution in the way consumers are looking at foods and beverages they purchase,” said Chavanne Hanson, a dietitian and nutritionist who serves as “wellness champion” at Nestlé USA, one of the 16 companies. “That challenges us, which is great for us and great for society because of how important it is to address the issue of calorie balance and the concerns we have from a public health standpoint about obesity and weight.”

Image General Mills has offered its Yoplait Greek 100 yogurt, with 100 calories. Other companies also started “healthy” foods.

To that end and toward their goal, companies have shrunk package sizes, eliminated oils, reduced sugar and salt and introduced new products.

Campbell’s, for example, introduced a number of “light” products, like Campbell’s Homestyle Light Italian Wedding Soup and diet V8 V-Fusion Plus Energy drinks with 10 calories in an 8-ounce serving. Jimmy Dean, a division of Hillshire Brands, began selling sausage crumbles made from turkey.