The British government has a new enemy: calories.

After cracking down on sugar and salt, Public Health England said Friday it now wanted companies to slash the calories in food to tackle an obesity epidemic among children.

It plans to set calorie targets for fast food and other meals popular with kids by the start of 2018.

"Ready meals, pizzas, burgers, savory snacks and sandwiches are the kinds of foods likely to be included in the program," the government's health body said in a statement.

Dominique Lemon, spokeswoman at Public Health England, said the program would cover food sold at all kinds of outlets, from grocery stores to coffee shops and fast food restaurants.

The government has already set similar targets for sugar and salt content.

The initiative could force food manufacturers to slash the size of their products and use different ingredients.

The new targets would be voluntary to start, Lemon said. But if the program doesn't work, the government would consider making the targets legally binding.

It's been down this road before, introducing a sugar tax on soda makers last year.

The U.K. introduced the tax as part of an effort to reduce childhood obesity. Drinks with total sugar content above 5 grams per 100 milliliters are affected by the levy with a higher rate ($0.30 per liter) for drinks with over 8 grams.

The measure appears to have worked. Rather than risk higher prices damaging sales, Coca-Cola (KO) and Pepsi (PEP) have already reduced the sugar content of many products.

The Food and Drink Federation said it welcomed the government's "whole diet" approach.

"We are pleased that the government has confirmed the broadening of its focus beyond just sugar -- and towards calories -- as it seeks to tackle obesity," Britain's food industry association said in a statement.

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Public Health England said British adults eat on average between 200 and 300 calories more than they need each day. One in three British children are either overweight or obese by the time they leave primary school. Children from disadvantaged backgrounds more likely to be obese.

"Reducing calorie consumption from sources other than sugar is critical to reversing the worrying obesity trend," it said in the statement.