I'll start this debate with an anecdote: My grandma, who raised me, also raised my father and my uncle in 1950s New York. She was a favorite mom on the block back in those days for one very good reason — she had saved up and gotten a "soda maker" and she made her own root beer and colas at home. She kept them cool in the basement. After school, her sons and their friends would come over to their place and down a soda — a cute story she shared with me many years later.

In the way that parents do, I remember that each time she told me about her soda-making days, she would remark on how small the glass soda bottles were (that she would reuse time and again), and how huge soda bottles were now (in the early '90s). She would shake her head and say "All that soda's no good for any one person! So much sugar ..."

As with a few other topics, my grandma was on to something. As soda serving sizes have increased, so have our waistlines, and even more upsetting, the incidence of obesity in kids has gone way up — but you know this, and almost everyone agrees we have to do something to change it.

Which brings me to the proposed NYC ban by Mayor Michael Bloomberg on soda servings larger than 16 ounces — and why I disagree with Jenn Savedge's thoughtful post about why she thinks the ban is a bad idea.

I argue that serving sizes matter. Tremendously.

And so do obesity researchers. Those who study obesity have for years reported that people look for social cues about how much food to eat — a bag of chips, a candy bar, a bottle of soda — that's a serving size (though the nutrition label shows the package might contain two or three servings). Almost anyone, if given a larger glass, will drink more; if they're given a larger plate, they will fill it with more food and eat more. According to a widely cited 2004 article in the journal Obesity, people use visual cues — not satiety — to determine how much to eat.

From the study: "Participants who were unknowingly eating from self-refilling bowls ate more soup than those eating from normal soup bowls. However, despite consuming 73% more, they did not believe they had consumed more, nor did they perceive themselves as more sated than those eating from normal bowls. This was unaffected by BMI."

The study authors go on to conclude: "These findings are consistent with the notion that the amount of food on a plate or bowl increases intake because it influences consumption norms and expectations and it lessens one's reliance on self-monitoring. It seems that people use their eyes to count calories and not their stomachs. The importance of having salient, accurate visual cues can play an important role in the prevention of unintentional overeating."

That's why a common tip from nutritionists is to buy smaller plates and glasses — because you will, for the most part, eat what's in front of you, whether that's a large plate packed with 1,000 calories, or a smaller one with 800. And studies show both will satiate you. But that extra 200 calories a day, times a year's worth of eating, means the difference between normal and overweight, or between overweight and obese.

I would also point out that we have a "control group" here of sorts: You can't get giant sodas in Europe, and nobody sees that as a "nanny state" issue, but just a cultural one. Europeans generally think giant portions are wasteful and fattening. Glasses are smaller there too, as are plates and food serving sizes — it all fits together. I would argue that the people there are healthier for it. What you see around you influences how much you consume.

In her piece, Jenn — and some other bloggers who agree with her — say that this is an issue of personal choice and liberty. I think being able to protest the government's choices, practice your religion (or speak about your atheism) freely, or homeschool your kids — those are questions of liberty worth fighting for in America. Serving sizes on soda? Not so much.

To be fair, Coca Cola seems to agree with Jenn's line of thinking. This is what the company, had to say: “The people of New York City are much smarter than the New York City Health Department believes. We are transparent with our consumers. They can see exactly how many calories are in every beverage we serve. We have prominently placed calorie counts on the front of our bottles and cans and in New York City, restaurants already post the calorie content of all their offerings and portion sizes — including soft drinks. (You can read more of the statement.)

We already have laws to keep people from ruining their local environment (even if they own that property), and laws against falsely yelling "Fire!" in a public building — because the best interests of the larger group goes before individual liberty. And when it comes to a national health crisis, this minor change in serving sizes doesn't look like a question of freedom to me, it looks like a small step to get Americans to rethink what a serving of soda looks like.

So for the millions of NYC school kids who head to the deli after school and get a smaller sized soda because that's all that's available to them, I don't think they're going to feel angry or deprived. As anyone who has made a dietary change knows, after a couple of days, it will just be the new normal. And that's a real step towards the fight against obesity and the lifelong health problems that being diabetic or overweight will bring. Because no amount of education, cajoling or even rewards will change the landscape much, but giving people less of what's bad for them might.

After all, it worked for smoking. According to Reuters: "In 2003, the city banned smoking in bars and restaurants, generating howls of protest at the time from smokers and non-smokers who saw it as a case of government creeping into private lives, but the law has since become widely accepted."

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