The proportion of Americans who are severely obese grew twice as fast in the five years up to 2005, as the proportion of moderately obese in the population.

The study was conducted by the RAND Corporation and will be published in the journal Public Health later this year.

Roland Sturm, author of the study and an economist at RAND, a non profit organization, said:

“The proportion of people at the high end of the weight scale continues to increase at a brisk rate despite increased public attention on the risks of obesity and the increased use of drastic weight loss strategies such as bariatric surgery.”

A severely obese person is someone whose body mass index (BMI) is 40 or more. This is about 100 pounds (46 kilos) above normal weight for an average man.

A typical severely obese man weighs 300 pounds (136 kilos) and has a height of 5 feet 10 inches (1.78 m), while a typical severely obese woman weighs 250 pounds (114 kilos) and has a height of 5 feet 4 inches (1.63 m).

The report states that since 3 per cent of Americans are already in the severely obese category, then widely accepted estimates for the impact on healthcare costs are underestimated because although they take into account the increased need for health services by the severely obese, they do not reflect the fact this is the fastest growing group.

The healthcare costs for the severely obese are considerably higher than for the moderately obese compared to people in the normal BMI range.

The average healthcare costs for a middle-aged person with a BMI over 40 is expected to be double that of someone of a similar age who is the normal BMI range. This compares with only a 25 per cent increase for those in the 30 to 35 BMI range.

The report states that from 2000 to 2005, the proportion of Americans with a BMI or 30 or more increased by 24 per cent, while the proportion of those with a BMI of 40 or more increased by 50 per cent.

The proportion of Americans whose BMI equals 50 or more went up by 75 per cent. Over the last 20 years the fastest growth has been toward the more obese end of the spectrum.

The report uses self-reported height and weight, which is thought to understate the real measures.

Bariatric surgery is a range of procedures that effectively reduce the amount of food that a patient can eat, for example by stapling the stomach to reduce its size.

The number of bariatric operations performed in the US increased from 13,000 in 1998 to over 100,000 in 2003. The figure is predicted to rise to 200,000 for 2006.

“The explosion in the use of bariatric surgery has made no noticeable dent in the trend of morbid obesity,” added Sturm.

He also said that the report challenges the misconception held by healthcare professionals that obese people comprise a fixed proportion, and remain unaffected by social and lifestyle changes in the general population.

The study suggests that clinically severe obesity is not a rare condition that only occurs in a fixed percentage of genetically vulnerable people, but is a feature of a population’s weight profile. As the overall population becomes heavier, the extremely overweight group is the one that grows the fastest.

How to Calculate Body Mass Index (BMI)

The formula for calculating BMI is:
BMI = Weight (in kilos) / Height (in metres) squared.

So a woman who weighs 154 lbs (70 kg) and is 5 ft 10 ins tall (1.79 m) has:
BMI = 70 / (1.79 x 1.79) = 21.9 which is in the Normal range.

BMI Healthy/Unhealthy Ranges

— Under 18.5 is classed as Underweight
— 18.5 to 24.9 is classed as Normal
— 25.0 to 29.9 is classed as Overweight
— 30 to 39.9 is classed as Obese
— 40 and over is classed as Severely Obese

Limitations of BMI

According to the US National Institutes of Health (NIH) healthy and unhealthy weight assessment takes into account three things:

(1) Body mass index (BMI),
(2) Waist circumference, and
(3) Risk factors for diseases and conditions associated with obesity.

BMI is not suitable as a healthy weight indicator for:

— Children and teenagers, because the BMI healthy/unhealthy ranges are based on adult heights.
— Athletes and bodybuilders because they have more muscle which distorts the results.
— Women who are pregnant (for obvious reasons!).
— Women who are breastfeeding (they need fat reserves).
— People over 65 who may also need a little more fat reserve incase they get ill.

Click here for American Obesity Association.

click here for online BMI calculator (pounds/feet or kilos/cm) from the Food Standards Agency (UK).

Written by: Catharine Paddock
Writer: Medical News Today