Whatever Washington does this year to reduce medical spending seems likely to be swamped by the nation's rising weight. Obesity lurks behind the top chronic illnesses - heart disease, diabetes, stroke, and colon, breast and prostate cancers, among many others - whose treatments routinely cost hundreds of thousands of dollars.

One of every three Americans, and one of every four Californians, is obese and rates are rising at an alarming pace, particularly among children, experts say.

"Rising obesity rates are increasing health care expenditures per person in a way that is going to be very difficult to finance," said Jay Bhattacharya, a doctor and health economist at Stanford University's Center for Primary Care and Outcomes Research.

"Unless there is some vast improvement in the efficiency of the health care system - and I mean vast - we're going to be spending a lot more just because a lot more people will have diabetes" and other obesity-related diseases, he said.

Obesity is all but impossible to treat. Prevention is the only cure. Yet while health care legislation in Congress would increase spending on prevention of chronic disease, it does little to tackle the underlying obesity epidemic directly. Most of the bills are silent on what many health experts contend would be one of the most effective weapons: a tax on soda.

Junk-food taxes are part of a push to adapt the successful fight against tobacco to the more complex obesity epidemic. Food, unlike tobacco, is necessary to life, and cheap food has all but eliminated hunger among the poor; yet there are many striking parallels between unhealthy eating and smoking.

State a leader in fight

California is proving a bellwether in the campaign against obesity, introducing novel prevention strategies under a remarkable collaboration between nonprofits and Gov. Arnold Schwarzenegger, a body-building Republican who launched his political career pushing fitness.

Legislation that took effect in the state July 1 has put calorie labeling on chain-restaurant menus, while nonprofits, led by the California Endowment, a health foundation, are conducting groundbreaking experiments that range from farmers' markets at Oakland schools to public park upgrades in the Salinas Valley town of Greenfield. California was the first to set nutrition standards for food sold in schools; now half the states do.

Still, such moves are up against a barrage of junk-food marketing, sedentary lifestyles, and federal farm and transportation policies that make processed fats and sugars cheaper than fresh food.

"We know exactly what to do about the obesity epidemic," said Harold Goldstein, executive director of the California Center for Public Health Advocacy in Davis. "Every successful public health movement, whether it was sanitation or air pollution or drunk driving or tobacco, has shown that people can only be healthy if there are policies in place that support them in making healthy choices."

Recipe for obesity

Imagine a vast national experiment to encourage weight gain, Goldstein said. "We put fast food on every corner, we put junk food in schools, we got rid of P.E., we put candy and soda at the checkout stand of every retail outlet you can think of .... The results are in. It worked."

San Francisco Mayor Gavin Newsom's plans to establish public vegetable plots and eliminate junk food from city property sounds preciously Left Coast but may be the vanguard of an ambitious national movement that aims to redesign cities and the way people eat.

Two Northern California cities - Arcata (Humboldt County) and Orinda - limit fast-food chains, while Los Angeles limited them in the South Central district after finding that 30 percent of children in those neighborhoods were obese.

Republicans on the House Energy and Commerce Committee mocked proposed jungle gyms and bike trails in health reform legislation, yet studies show such efforts help.

"It doesn't sound crazy if you start looking at the causes of the problem," said Kelly Brownell, an obesity researcher at Yale University's Rudd Center for Food Policy and Obesity. "In poor neighborhoods there is low access to healthy foods, high access to calorie-dense, nutrient-poor foods, and when healthy foods are available, they're more expensive."

The same holds for physical activity, where crime, poor facilities and parents working multiple jobs limit opportunities for safe play. "You put all this together," Brownell said, "and you have a picture that is maximizing calorie intake and minimizing calorie output, and there's your recipe for obesity."

Epidemic hit quickly

Life expectancy in the nation, rising since the Civil War to nearly 78 years now, could be halted or even rolled back as a result of Americans' weight gain and the chronic diseases that accompany it, many experts believe.

The obesity epidemic took hold over just one generation, a stunningly short period in the history of public health, said Marion Standish, program director for the California Endowment. Efforts to change individual behaviors have failed miserably; researchers now are focused on changing the environment that has fostered weight gain to prevent obesity in the first place.

"Policymakers who ignore or ridicule prevention do so at their own peril," Standish said. "Cost data just released by the Centers for Disease Control show there is no doubt the health care system is going to bear the brunt of this challenge."

E-mail Carolyn Lochhead at clochhead@sfchronicle.com.

This article appeared on page A - 1 of the San Francisco Chronicle