The battle of the bulge is being fought by the preschool set.

According to a striking new study, nearly one in five 4-year-olds is obese. More than half a million U.S. children are dangerously overweight before they enter kindergarten, increasing their likelihood of becoming obese adults.

Children that young have little or no control over their diets and activities, so it is up to adults to make the necessary lifestyle changes to help them maintain healthy weights.

Why worry about baby fat? Because research confirms the health and economic consequences caused by obesity. Since 1980, as the average weight of Americans has increased, so have the rates of high blood pressure, cholesterol, diabetes, heart disease and other related health issues. Obesity costs America tens of billions annually through increased health care costs and loss of productivity.

And the problem is showing up earlier. Thirty years ago, 5 to 7 percent of school-aged kids were obese. By 2003, it was up to nearly 18 percent, and rates of childhood Type II diabetes were growing.

Now waistlines are widening even among children who are barely out of diapers. A study released this week by Ohio State and Temple university scholars analyzed 8,550 preschoolers born in 2001. The survey found that about 20 percent were obese, and there were disturbing disparities by race. American Indian children had the highest obesity rates at 31 percent, followed by 22 percent of Hispanics, 21 percent of African-Americans, 16 percent of whites and 13 percent of Asians.

The figures show a direct tie to poverty. Lower-income communities tend to have less access to healthy, affordable foods, so families tend to consume cheaper, high-calorie items. Poverty-related stress and depression can also increase sedentary lifestyles. In high-crime communities, parents may limit outdoor play to keep children safe. And many schools under pressure to improve achievement have cut back on physical education.

Obesity rates in some populations merit special attention, but the overall percentages are equally disturbing. As kids get heavier, some experts predict that this could be the first generation of Americans who will be sicker and die younger than their parents.

Solving the problem involves a simple, well-known formula: Exercise and eat less and healthier.

To that end, the federal 2008 Food Conservation and Energy Act is providing grants to help schools offer healthy snacks. And under Minnesota’s $47 million Statewide Health Improvement Program (SHIP), state community health boards and tribal governments are receiving funds to reduce the burdens of preventable causes of illness and death — including obesity. SHIP grants will, for example, support increased availability of nutritious foods in low-income neighborhoods and encourage more options for walking, biking and other physical activity.

Better for government, communities and families to invest in reducing youth obesity now — starting with preschoolers — than to pay billions later.