For many years, experts have raised a red flag: the US is becoming a fat nation. In our daily life, junk food, fat and fast food are everywhere at work, at home, at the malls, at the ballpark. The consequence: an estimated 64 percent of Americans today are either overweight or obese, according to the Centers for Disease Control and Prevention.

Poor nutrition and physical inactivity account for some 300,000 premature deaths in the U.S. each year due to diabetes, heart disease, cancer and other illnesses. Obesity costs the U.S. $117 billion a year.

So what is there to do about this huge problem? The strategy so far has been to tell people that being overweight is unhealthy and they should change their diet and exercise more. But many argue that hasn't worked terribly well. After all, despite all this advice, Americans are fatter than ever.

So now some nutrition experts and consumer groups are calling for a "war on obesity," more dramatic actions that would give clear incentives for people to stop eating so much. One proposal on the table is the creation of a fat-tax, adding a small tax on high calorie food such as sugary sodas, candies and snack food to finance programs to improve diet and activity.

But taxing junk food raises questions. What is obesity? Just an individual problem or a societal one? A question of self-discipline or of environment?