A new weight assessment method could help in the global fight against obesity, writes Theresa Judge
A new method to assess a person's weight, providing an alternative to the commonly-used Body Mass Index (BMI), has been unveiled in Britain.
The Body Volume Index (BVI) uses a 3D imaging scanner and has the potential to be more informative than BMI because it could show where on the body fat is stored. It is known that fat stored around the stomach area is associated with cardiovascular disease and diabetes.
BMI, which is a ratio of weight to height, has been the standard measure used in studies over recent decades that have consistently found a link between obesity and a range of conditions including cardiovascular disease, stroke, diabetes, osteoarthritis and cancer.
A BMI of more than 25 is associated with a slightly increased risk of these conditions, while a BMI of more than 30 puts a person at an even greater risk. The main shortcomings of BMI as a measure is that it does not distinguish between muscle and fat and it does not tell us anything about how fat is distributed on the body, says Margot Brennan of the Irish Nutrition and Dietetics Institute.
She points out, for example, that an athlete such as rugby player Brian O'Driscoll would have a very high BMI because of the amount of muscle on his body and because muscle is heavier than fat.
Dr Donal O'Shea, a consultant who specialises in obesity, says there is "a clear recognition that where the fat is on the body is very important".
Being able to assess this would give more realistic and more relevant information, he says.
While it is known that the distribution of fat is relevant to the risk of cardiovascular disease and diabetes, we do not know if this is significant for the risk of cancer or osteoarthritis, he says.
"BMI is under pressure as a key measure of weight, but it isn't yet clear what can replace it," says O'Shea, who runs an obesity clinic in Loughlinstown hospital, Dublin and who also works in St Vincent's hospital in Dublin. He points out that all the information we have relating weight to excess risk of various illnesses is based on BMI, so it would be difficult to interpret findings based on a body volume index.
While a measurement based on body volume is likely to be useful for assessing cardivascular risk, it is not known how useful it would be for assessing risk of cancer or osteoarthritis and more studies would be needed to determine this, he says.
He believes that waist circumferance is a measure that should be used routinely in clinical practice rather than relying solely on BMI. Waist measures of more than 35 inches for a woman and 40 inches for a man are regarded as dangerous.
O'Shea also points out that there are currently scanning devices that can show fat distribution, for example, a scan designed to measure bone density, but it is not generally used for this purpose.
The obesity unit in Loughlinstown hospital is also currently participating in an international study taking single-site CT scans of people's abdomens to assess how fat in this area can affect health.
Although there are criticisms of BMI, Brennan points out that it also has advantages because it is easy to calculate and does not require any expensive equipment.
It can also be used on a wide range of groups such as the elderly in nursing homes, and for people who may be underweight because of eating disorders, she says.
When used in conjunction with waist circumferance it gives a very good indication of whether a person's weight is at dangerous levels.
Nutritionist Paula Mee believes the body volume index could prove more useful to motivate people who are trying to lose weight. "It's hard for people when they go up on the scales and see they've only lost two pounds, but if you could show them that there was a change in body composition with more muscle and less of the harmful fat, that would be great," she says.
Fat that is stored around the middle is more harmful than fat in other areas such as the thighs and buttocks.
However, "it is the first to shift when you start to exercise," says Mee.
She says it is critical that ways are found to help people understand how fat damages organs and fears that with an increasing number of people being overweight there may be some complacency.
"We need to do more to motivate people to lose weight," says Mee.
"Because more than half the population is overweight now, people may almost feel safe in numbers and not realise the dangers," she explains.