Americans have access to the same food in every state. You will find the same soda in Tennessee as you will in Oregon. Fast-food franchises serve the same hamburgers in Arizona and in New Hampshire. Arkansas residents can buy the same packaged foods as residents of Ohio. Everyone, in every state, gets to decide what food to buy. Yet obesity rates vary widely across the country. With only a fifth of its residents officially fat, Colorado is the leanest state, while Mississippians, a third of whom are obese, are the fattest.

These differences are puzzling to those convinced that obesity is simply the result of eating too much, or the wrong things. Do people in Mississippi really have the biggest appetites? State-by-state obesity trends make more sense when you look at the other side of the obesity equation: physical activity. Simply put, residents of states with high obesity rates tend to move less.

On a recent visit to Colorado, Kansas’ Wichita Eagle food editor Joe Stumpe noticed that Colorado had all the usual fast-food eateries. So why is the state leaner than Kansas (which ranks 19th fattest in the nation)? “[T]he answer,” Stumpe says, “does appear to involve walking, running, skiing, boating, biking and a host of other physical activities. Colorado residents just seem to be more active than people in a lot of other states.”

This observation was echoed by co-founder of the National Weight Control Registry, James Hill. He suggests that people’s failure to get trimmer can be attributed in large part to our narrow, food-only approach. “We focus too much on diet and not enough on physical activity,” he says.

Both Stumpe and Hill’s hunches are backed by the facts. Of the top 10 most-obese states, government surveys show nine of them are also the most sedentary. The residents of the most obese state — Mississippi — report the lowest rates of leisure-time physical activity in the country.

Are fast-food outlets too numerous? Census statistics indicate that none of the top 10 obese states have the most fast-food restaurants per person. And seven out of those ten “fat” states rank in the 15 lowest concentration of fast food. In fact, the heaviest state — Mississippi — is third lowest in the country. Colorado — the leanest state — is among the ten states that have the highest concentration of fast-food restaurants.

This reality is mirrored by scholarly studies. A 2007 study published in the International Journal of Obesity concludes, “The obesity epidemic is often speculatively blamed on fast food, when the actual evidence shows very little, if any, association of fast food with weight gain.” There is an unambiguous relationship between physical inactivity and obesity in the United States. At the same time, there is no clear relationship between obesity and access to fast-food restaurants.

The self-appointed food police in society don’t like those facts.

Because controlling food prices or availability is easier than controlling people’s physical activity, these activists push for new laws that range from warning labels to new taxes on anything caloric.

The ultimate goal of food activists is the prohibition of high-calorie foods. As one activist put it, “there is no difference between Ronald McDonald and Joe Camel.” Statistics tell us that the nutritional content of our meals is virtually unchanged from a half-century ago, but fewer of us are burning off the calories we ingest. If there’s a lesson to learn from Colorado, it’s this: Have a soft drink with lunch, or a beer with your dinner — but don’t forget to go for a walk. If they can do it in Denver, so can you.