PALO ALTO, CA — Body mass index (BMI), calculated as weight in kilograms divided by height in meters squared, has been established as a tool to evaluate the risk of obesity-related health conditions and mortality. A BMI of 30 or higher, the standard definition of obesity, is widely adopted by health organizations such as the World Health Organization, the national Centers for Disease Control and Prevention and the National Institutes of Health.
A new study by researchers at the Palo Alto VA Medical Center indicated that the presence of additional metabolic conditions is also a strong predictor of the risk of developing further comorbidities over time.
The study’s first author, Yang (Frank) Lu, MD, became interested in metabolic risk factors as a minimally invasive surgery/advanced GI fellow at the Palo Alto, CA, VAMCl. To qualify for bariatric surgery, his patients’ BMI had to be above a certain threshold, but those thresholds were somewhat arbitrary, he said. He wanted to know how effective BMI was at predicting risk factors for metabolic disease and if focusing on BMI, might cause doctors to miss other important risk factors for metabolic disease.
“BMI has a very significant relationship with developing metabolic risk factors and that is why it’s thought that by lowering BMI, patients can reduce their risk for metabolic disease,” he told U.S. Medicine. “But we wanted to see how important other factors such as preexisting metabolic conditions were. So, for example, if someone is obese at baseline, but has no medical co-morbidities, how likely are they to develop medical co-morbidities in five years, if the only risk factor is obesity?”
To answer those questions, Lu and his colleagues turned to data from the VHA Corporate Data Warehouse. The researchers analyzed data from a random sample of veterans receiving care within VHA who had complete height, weight and comorbidities data and one more than one primary care between FY 2005-2007.1
Using BMI and the presence of four obesity-related comorbidities—Type 2 diabetes, hyperlipidemia/dyslipidemia, hypertension, or nonalcoholic fatty liver disease—the researchers divided the veterans into four cohorts: metabolically healthy lean (MHL) veterans, metabolically unhealthy lean (MUL) veterans, metabolically healthy obese (MHO) veterans and metabolic unhealthy obese (MUO) veterans. Obese was defined as having a BMI of 30 or greater. Healthy was defined as the absence of any comorbidity, and unhealthy was defined by the presence of one or more comorbidities. They then followed the veterans for development of new or additional metabolic conditions over a 5-year interval.
Of the 66,259 veterans studied, 7661 (6.9%) were classified in the MHL group, 17217 (15.5%) in MUL group, 6267 (5.7%) in MHO group and 35114 (31.7%) in MUO group at the index date, the researchers reported in JAMA Surgery. Overall, there were 27.5% with Type 2 diabetes, 48.9% with hyperlipidemia, 67.0% with hypertension and 1.2% with nonalcoholic fatty liver disease.
At the index date, individuals in the MUO group were significantly more likely to have Type 2 diabetes or hyperlipidemia compared to those in the MUL group. The MHL and MHO groups had no comorbidities at baseline. However, after 5 years, 3% of individuals in the MHL group developed diabetes, 23% developed hyperlipidemia, and 24% developed hypertension, although at rates lower than those observed in the MUL group (6%, 28%, and 34%, respectively). Similarly, after 5 years, 12% of individuals in the MHO group developed diabetes, 38% developed hyperlipidemia, and 36% developed hypertension, compared to 20%, 44% and 50%, respectively, in the MUO group. There was no significant difference in the risk of developing nonalcoholic fatty liver disease (NAFLD) between the MUO and MHO groups.
“BMI does still matter, because the higher the BMI the higher the likelihood of developing comorbidities,” Lu said. “But along with that, just having other metabolic comorbidities significantly impacts the trajectory,” he said, adding that he was surprised at how much of an impact having a comorbidity at baseline had on the development of comorbidities at 5-year follow-up.
“I think there’s increased awareness recently in national societies that we need to develop a more comprehensive risk-assessment framework beyond BMI alone that may incorporate other physiologic or genetic factors that impact metabolic health,” he added. “If we are able to make these improvements and make the risk assessment framework better, that could maybe enhance eligibility criteria for metabolic bariatric surgery and could also help us better allocate resources to more at-risk populations,” he said.
For now, Lu said the study sends a message to primary care physicians who have patients struggling with metabolic disease. “Even if a patient’s BMI doesn’t reach a certain threshold, it might be worth a referral to or discussion with a bariatrician to see what resources are available to protect against the development of further metabolic disease,” he said.
- Lu Y, Arnow K, Eisenberg D. Risk Factors for Metabolic Disease in Veterans: Beyond BMI. JAMA Surg. 2024 Nov 27. doi: 10.1001/jamasurg.2024.4518. Epub ahead of print. PMID: 39602137.
