A New York tactic to fight obesity will see soft drink serves restricted to 500ml or less.
After obesity rates in the United States began soaring in the 1980s, federal, state and local governments started to push back. Calorie counts were mandated for food packages and in many restaurants. School lunches were made healthier. Unhealthy trans fats got phased out.
Yet American waistlines continued to swell, with two-thirds of adults and one-third of children now overweight or obese - a major factor in the country's health-care crisis, as obesity triggers expensive chronic illnesses, including diabetes and heart disease.
By the early 2000s, policymakers began focusing their energies on a new target - soft drinks.
High in calories and with no nutritional value, soft drinks are a huge source of added sugar in the diet. Study after study shows that people who drink the most non-diet soft drinks are at the highest risk for obesity.
But in the face of intense lobbying from drink makers, efforts to tax and regulate soft drinks have foundered.
This past week, New York Mayor Michael Bloomberg - amidst a multi-front war on obesity - tried a new tactic. He proposed limiting sugary drinks sold by restaurants, cinemas, street vendors and stadiums in his city to 500ml.
Grocery stores would be exempted.
"We know that portion size influences consumption. We know that portion sizes have risen dramatically. And we know that sugary drinks have this uniquely strong connection with weight gain," Stuff.co.nz quoted Thomas Farley, New York's health commissioner, as saying.
The move intensified the debate over how far government should go to steer individual behaviour in the name of health and immediately drew scorn from the US 75 billion-dollar-per-year (NZ 99.4 billion-dollar-per-year) soft drink industry.
"Here they go again," Chris Gindlesperger, spokesman for the American Beverage Association, an industry group, said.
"The New York City health department has an unhealthy obsession with attacking soft drinks. It's over the top. It's overreach. The city is not going to address the obesity problem by attacking soda, because soda is not driving the obesity rate," he said.
A group funded by restaurants began running ads in New York branding Bloomberg - shown in a housedress and scarf - as "the nanny".
"You only thought you lived in the land of the free," read the newspaper ad bought by the Centre for Consumer Freedom, which sourcewatch.org says represents the restaurant, alcohol, tobacco and other industries.
Fast-food giant McDonald's also weighed in with a tweet to Bloomberg on Friday, "We trust our customers to make the choices that are best for them."
But public-health advocates contend that letting everyone make their own choices has led the country to 192 billion dollars (NZ 255 billion dollars) per year in medical bills for obesity-related care. That's a tab everyone ends up paying via Medicare, Medicaid and soaring rates for private health insurance.
"There is nobody on face of the planet who needs a soda, let alone a 1000ml soda," Robert Lustig, a pediatric-obesity researcher at the University of California at San Francisco who is a vocal proponent of restrictions on sugary drinks, said.
Advocates of soda regulation point to a long list of government mandates - vaccines to prevent childhood diseases, seat-belt laws and automobile-air-bag rules, and high taxes and age restrictions on cigarettes and alcohol - that they say have improved public health and saved lives.
What sets New York's proposal apart is that it addresses a new aspect of the obesity problem - portion size.
"If New York City's initiative succeeds, it really opens up a new front," Michael Jacobson, executive director for Center for Science in the Public Interest, an advocacy group, said.
"I'm sure it will encourage other cities and states to seek similar measures to reduce portion sizes," he said.
The approach also offers a model for getting around the kind of political warfare that has impeded soda taxes, Farley said.
The battle over soft drinks raged in 2009, after President Barack Obama floated the idea of a national soda tax to reduce consumption and pay for his proposed health-care reforms. As top academics championed the idea, states and cities rolled out proposed taxes.
Experts disagree about whether the Bloomberg plan will cut into the city's obesity problem.
"There's not a lot of evidence it will work," Cornell University professor Brian Wansink, who studies food behaviours, said.
"Because the people who drink it really like it, they're going to figure out a way around it," he said.
But a slew of research shows larger cups and bottles leads to more soda drinking.
"What's put in front of you, big or small, feels satisfying to people," Farley said.
Barry Popkin, a prominent public-health researcher at the University of North Carolina, agreed, calling the proposal "gutsy".
"Controlling sugary beverage portions . . . is critical for reducing weight gain and risk of diabetes in the United States," Popkin said.
Brownell challenged the industry groups accusing Bloomberg of cutting into Americans' freedom to choose,
"It's not a nanny state to encourage people not to buy a 64-ounce soda at KFC," Brownell added.