HOW’S THIS for an unlikely weapon against obesity: On 10-year-old Ezra Fellman-Blau’s first visit to the child-obesity clinic at Children’s Hospital, Dr. David Ludwig offers the boy a piece of chocolate.

It’s dark chocolate, specifically - the rich, bitter stuff - and Ludwig first explains that, unlike milk chocolate, this is a health food. Then he gives Ezra a lesson in how to eat. Smell your food. Then lick it. Then chew it slowly. Swallow. Take note of every sensation, in your mouth and in your stomach.

It’s an experiment in what Ludwig calls “mindful eating,’’ and it highlights one of the many ways our relationship with food has been distorted. “We’re taught to eat things unconsciously,’’ he says. We gobble down foods that are salty or sweet, shy away from complex flavors, label some foods that are good for us as unhealthy, and vice versa. We think that counting calories and vilifying fat will help us get thin.

When it comes to fighting childhood obesity, “I don’t think food is the problem,’’ Ludwig said. “I think food is the answer.’’

The problem, it turns, out, is much harder to address.

And the problem is growing, nationwide and close to home. Today, one-third of Massachusetts children are overweight or obese, according to a recent report from the Boston Foundation and the New England Healthcare Institute. In 2009, nearly half of the state’s public school students attended no gym classes at all.

The health implications are pressing, and so are the costs: Phil Edmundson, a Boston insurance company chief who is spearheading his own anti-obesity campaign, notes that obesity-related illnesses account for nearly a third of the increase in health care costs. At Ludwig’s clinic - known as OWL, for Optimal Weight for Life - many patients are at risk of diabetes, heart disease, and other chronic illnesses that could lead to premature death.