Body mass index an 'inadequate' measurement of obesity, experts say

BMI measures the ratio of a person’s height to weight to estimate body fat, but has been questioned in recent times.

Body mass index (BMI) should not be the only measurement for obesity, with more in-depth medical assessment required, global experts in the Lancet Commission have said.

People with obesity should be in two groups based on the level of threat to their lives from this condition, the commission advised in London on Thursday 

Professor Carel le Roux, Irish Society for Clinical Nutrition and Metabolism president and commission member, said this would help target health spending.

BMI measures the ratio of a person’s height to weight to estimate body fat, but has been questioned in recent times. 

Now, the commission said it could “underestimate and overestimate" body fat and gave "inadequate information about health". 

Instead, it advised “either direct measurement of body fat” or BMI, in addition to measuring “waist circumference, waist-to-hip ratio, or waist-to-height ratio” be used.

The commission argued everyone with obesity was usually discussed as a single group defined by BMI, but they have different health needs.

Instead, it advocated for assessing people with the most serious health risks under a "clinical obesity" label.

These people have “reduced organ function (such as breathlessness or heart failure) and / or have substantial trouble with movement and day-to-day activities such as bathing, dressing, eating and continence — due to excess body fat". 

A second group, under a "preclinical obesity" label, would include people facing “increased future health risk”.

They are at risk, for example, of developing type 2 diabetes, cardiovascular disease and some cancers. 

The 58 doctors, patients and other experts acknowledged the move away from BMI could lead to extra costs in healthcare.

“However, continuing with the current inaccurate diagnostic framework could lead to even greater burden and costs, both to health systems and to individuals living with obesity,” they said.

Prof Le Roux said: “We can now start a serious conversation about how we can work together and move away from the idea of weight-loss to the idea of health gain to address both clinical obesity and preclinical obesity." 

He added it was important to have an “agreed language and understanding” among patients, healthcare workers and anyone working with obesity.

An estimated 1.25 million people in Ireland — 24% of the population — live with obesity.

The commission’s paper is in the Lancet Diabetes and Endocrinology journal.