Since mid-1970s, the prevalence of overweight and obesity has increased sharply for the US and this thing is clearly shown by the latest report on obesity rates of the US Centers for Disease Control and Prevention released on Thursday.

The report was based on a telephone survey of 350,000 adults who were interviewed on their height and weight, two measures important for calculating a person’s body mass index.

A BMI above 30 is classed as clinically obese, a BMI between 25 and 30 is classed as overweight, while a BMI between 20 and 25 is classed as normal, healthy weight.

According to the report, the number of adults who say they are obese jumped 2 percent between 2005 and 2007, from 23.9 percent in 2005 to 25.6 percent in 2007, that excepting people who are overweight. More exactly, 1 is 4 Americans is obese, the CDC found, which is of high concern for us health officials.

“The epidemic of adult obesity continues to rise in the United States, indicating that we need to step up our efforts at the national, state, and local levels. We need to encourage people to eat more fruits and vegetables, engage in more physical activity, and reduce the consumption of high-calorie foods and sugar-sweetened beverages in order to maintain a healthy weight,” Dr. William Diets, director of CDC’s Division of Nutrition, Physical Activity, and Obesity said in a news release.

According to the report, the percentage of obese people varies by state and region. In the South, 27 percent of residents were obese, the highest rate of all regions. In the Midwest, the number was 25.3 percent; in the Northeast, 23.3 percent; and in the West, 22.1 percent.

Kentucky, Virginia, South Carolina, Louisiana and West Virginia were the only states where obesity was less prevalent in 2007 than in 2005. Colorado had the lowest prevalence of obesity, at 18.7 percent, rising from 17.4 in 2005.

At the opposite side were Mississippi, Alabama and Tennessee, which led the nation when it comes to obesity, with more than 30 percent of obese people. Mississippi has had the highest obesity rate since 2004.

Dietz blamed the traditional southern diet, which is high in fat food and fried food, for the high rate if people who are obese in these states. Also, the majority of people in South are either black or living in rural areas, two groups that tend to have higher obesity rates.

Poverty in the South could be another factor for the high obesity rates. The cheapest foods tend to be heavy in calories and stores with more expensive food but healthier are not often found in poor neighborhoods.

Other factor influencing the obesity rates were educational levels. For example, for men, obesity prevalence was lowest among college graduates (22.1 percent) and highest among those with some college (29.6 percent) and high school diploma (29.1 percent). For women, obesity prevalence was lowest among college graduates (17.9 percent) and highest among those with less than a high school diploma (32.6 percent).

The CDC said the data they have on obesity could be irrelevant because the survey based on what respondents said about their height and weight. It is known that men commonly overstate their height and women often lowball their weight.

“The heavier you are, the more you underestimate your weight, probably because you don't weigh yourself as often,” Dietz said.

The findings are the more worrisome as one of the national health objectives for the year 2010 is to reduce the prevalence of obesity to less than 15 percent. Current data show that the situation is worsening rather than improving.

The findings raise concern because of the implications of obesity for Americans’ health. Being overweight or obese has been linked to serious health conditions such as high blood pressure, osteoarthritis, type 2 diabetes, high levels of cholesterol or triglyceride, coronary heart disease, stroke, sleep apnea and respiratory problems or even some cancers (endometrial, breast and colon).

The findings were published in the July 18 issue of the CDC’s Morbidity and Mortality Weekly Report.