Rethinking how we measure healthy body weight
Research finds using body mass index (BMI) alone may miss serious health problems
Thousands of middle-aged Canadians thought to have normal levels of body fat may be carrying extra weight in areas that significantly increase their risk of serious health problems and even death, according to a new study by University of Calgary researchers.
Recent evidence suggests that high amounts of fat in the body, and inflammation resulting from fat, may be at the root of many chronic diseases. However, Canada and most other developed countries commonly use weight in relation to height, a measure called body mass index (BMI), to classify individuals as normal weight, overweight or obese. This total-body approach does not measure specific locations, such as the waist, where a large percentage of an individual’s body fat may collect. As a result, some individuals with a normal BMI can have as much fat as those with an elevated BMI.
“Our study found that middle-aged individuals between the ages of 40 and 69 who were classified as having normal BMI actually had a greater than 50 per cent chance of being reclassified as overweight or obese when body fat accumulated in specific locations of the body was measured,” said Behnam Sharif, PhD, one of the study’s authors and an Alberta Bone and Joint Health Institute (ABJHI) postdoctoral fellow at UCalgary. “These individuals may be at risk for obesity-linked health problems, such as arthritis, cancer, diabetes and heart disease, but would not be identified as such based on their BMI classification.”
“We may be missing opportunities to intervene with health strategies, such as diet and exercise, to avert health problems, some of which are life-threatening, in a large segment of Canada’s population,” said Deborah Marshall, PhD, professor in the departments of Community Health Sciences and Medicine at the Cumming School of Medicine, and ABJHI’s director of research.
The problem may affect almost one-third of middle-aged Canadians. Women were most at risk of a missed diagnosis of being overweight or obese when their BMI was measured. The findings are published in the Canadian Journal of Public Health.
The researchers found studies showing middle-aged individuals have a two-fold increase in the rate of death from heart disease and other cardiovascular events, compared with other age groups.
“The reason for this increased risk for chronic diseases may be a correlation between increased body fat, location-specific body fat, inflammation related to body fat, and elevated levels of metabolic risk factors such as high blood sugar and hypertension,” said Kelsey Collins, PhD candidate in the Biomedical Engineering (BME) Graduate Program and lead author. “We do not currently measure body fat or lean body mass directly in patients. Collecting these data is critical to increasing our understanding of the triggers of chronic disease and to determining who may be at risk.”
“Our findings highlight the need for developing and implementing new triaging strategies that accurately measure body composition in middle-aged non-obese individuals and can be used in primary care settings to identify those who may benefit most from prevention,” added Marshall.
The study used information collected by Statistics Canada in its Canadian Health Measures Survey from 2007 to 2011. The study was funded by a grant from Alberta Innovates (Osteoarthritis Team grant).
From left Deborah Marshall – PhD, Behnam Sharif – PhD
Kelsey Collins – PhD candidate
Behnam Sharif, PhD, is trainee of the Cumming School of Medicine’s McCaig Institute for Bone and Joint Health. Deborah Marshall, PhD, is a member of the McCaig Institute for Bone and Joint Health and the O’Brien Institute for Public Health. Kelsey Collins is a McCaig Institute Trainee and a member of the Faculty of Kinesiology’s Human Performance Laboratory, University of Calgary.
Other members of the research team were Dr. Claudia Sanmartin, Statistics Canada; Drs. Walter Herzog, Raylene Reimer, and Rick Chin, University of Calgary.