Americans are getting heavier than ever, with more than 26 percent of the population now fully obese, the U.S. government reported on Wednesday.

Despite warnings that the population must stop layering on the fat and frightening statistics that show two-thirds of Americans are overweight or obese, the weight trend continues, the U.S. Centers for Disease Control and Prevention reported.

The proportion of U.S. adults who are obese increased to 26.1 percent in 2008 compared to 25.6 percent in 2007, the CDC said in a statement.

If this trend continues we will likely see increases in healthcare costs for obesity-related diseases, said the CDC's Liping Pan, who headed the study.

Obesity is a major risk factor for many chronic diseases such as heart disease and diabetes, the CDC's Dr. William Dietz added in a statement. As obesity increases among all age groups, we are seeing chronic diseases in much younger adults compared to a few decades ago.

For example, we now see young adults who suffer from heart disease risk factors and other conditions such as type 2 diabetes that were unheard of in the past.

The agency used its Behavioral Risk Factor Surveillance System, a telephone survey of 400,000 adults, to gather its data.

At least 30 percent of adults are obese in six states -- Alabama, Mississippi, Oklahoma, South Carolina, Tennessee and West Virginia, the CDC found.

Only Colorado can claim that fewer than 20 percent of its residents are obese.

Last week the Trust for America's Health and Robert Wood Johnson Foundation released a similar report showing residents of 23 U.S. states are fatter now than they were a year ago.

Body mass index, a measure of height to weight, is used to calculate obesity. A person is considered overweight with a BMI of 25 or more and obese with a BMI of 30 or above.

BMI is equal to weight in kilograms divided by height in meters squared. Someone 6 feet 2 inches tall and weighing 240 pounds (109 kgs) would be obese and would have to get below 195 pounds (88.5 kg) to be no longer considered overweight.

The U.S. National Institutes of Health has an online BMI calculator