Washington (AFP) - Americans have got fatter over the past two decades, adding girth to their bellies and even growing fractionally shorter on average, according to federal health data released Thursday.

The report gave no specific reasons for the trends, which come as no surprise as the nation battles with an ongoing obesity epidemic and a record 40 percent of Americans are considered obese.

Average weight, waist circumference, and body mass index (BMI) in adults have increased over the past 18 years, said the report by the National Center for Health Statistics.

"A significant linear increase in body weight was seen over time for both men and women," said the report, based on data from physical exams on more than 47,000 people nationwide over the age of 20.

The average American man weighs 197.9 pounds (89.8 kilograms), according to the most recent year for which data is available, 2015-2016.

That's up eight pounds from 1999-2000, when the average male body weight was 189 (86 kg).

Women have packed on the pounds too, going from an average of 164 lbs (74 kg) in 1999 to 171 lb (77 kg) in 18 years.

Men's average waist size has crept from 39 to 40 inches (99 cm to 102 cm), while women's waists grew three inches -- 36 to 39 inches (92 to 98 cm) -- in that time span.

American men today are slightly shorter: five foot 9.2 inches (175.6 cm) in 1999, and five foot 9.1 inches (175.4 cm) by 2015.

Women's average height also fell one tenth of an inch since 1999.

BMI, a key health indicator which is calculated as ratio of height and weight, showed men climbed from an average of 27.8 in 1999 to 29.1 in 2015.

Women went from a 27.8 to 28.2.

Those BMIs put both men and women squarely in the "overweight" range -- the normal range is typically 18.5-24.9.

According to the latest data from the Centers for Disease Control and Prevention, 39.8 percent of Americans are considered obese, a total of more than 93 million people.

Doctors say there are plenty of reasons to maintain a normal weight, as obesity raises the risk of heart disease, stroke, type 2 diabetes and certain types of cancer.

Obesity also packs a punch to the economy. The estimated annual medical cost in the United States is $147 billion, according to the CDC.