Dr. Francisco Lopez-Jimenez of the Mayo Clinic in the United States told a National Obesity Forum conference that one out of every five subjects with normal Body Mass Index has excess body fat, putting them at risk of metabolic abnormalities that lead to diabetes and heart disease, the Daily Telegraph reported Monday.

Lopez-Jimenez said current reports -- that 66 percent of British adults are either overweight or obese -- understate the problem. He said the number is more likely to be at least 75 percent.

"This clearly highlights that healthcare professionals must adopt body composition monitoring at an individual level to avoid mis-classifying patients with excess body fat as non-obese," he said.