Basic BMI measurements more effective than genetics in predicting how obese you will be in future, says study
Even as genetics get increasingly popular in studying and identifying health risks in individuals, researchers now suggest that a person’s body mass index (BMI) can better predict how obese the individual will be in the future, as compared to genetic risk profiling.
Researchers from the Michigan Medicine Frankel Cardiovascular Center and the Massachusetts General Hospital Cardiovascular Research Center evaluated health data of over 2,517 young adults from across the US. They volunteered to participate in a longitudinal study 25 years ago. The assessments included polygenic risk of obesity, fitness, activity and BMI in young adults (in their 20s), up to 25 years of follow-up.
The researchers found that baseline BMI in young adulthood explained 52.3% of a person's BMI 25 years later when it was considered in combination with age, sex and history of a parent ever being very overweight. The prediction could explain up to around 80% of BMI variation after following someone's BMI over time, rather than just at baseline and 25 years later, says the research team.
Those same combinations of age, sex and parental weight history were then considered with a polygenic risk score instead of BMI. They found that a polygenic risk score could only explain 13.6% of BMI variation in midlife and 11.9% at year zero.
“If we don’t know a person’s BMI at baseline (in this case at age 18-30), then the combination of age, race, sex, parental history of overweight/obesity and polygenic risk score accounted for about 13-14% of BMI variation over 25 years. Conversely, knowing the BMI at baseline, in addition to age, race, sex and parental history of overweight/obesity accounted for greater than 50% of BMI variation over 25 years,” lead author Dr. Venkatesh Murthy, a cardiologist at the Frankel CVC, told MEA WorldWide (MEAWW).
According to the World Health Organization (WHO), nearly 2 billion adults worldwide were overweight and, of these, more than half a billion were obese in 2016.
Experts caution against widespread use of genetic risk scores
The data in CARDIA (Coronary Artery Risk Development in Young Adults) was collected between March 1985 and August 2011 to explore the development of cardiovascular diseases.
“Polygenic risk scores did not offer an accurate prediction of BMI in midlife, whereas BMI in young adulthood offered a more accurate prediction of long-term BMI trends,” says the study.
Based on the findings, published in JAMA Cardiology, the researchers say that a person's BMI measurement from 25 years ago was a better predictor of their current BMI than a polygenic risk score.
Murthy, an associate professor of internal medicine and radiology, says baseline fitness had greater predictive value than genetics when knowledge of a person’s BMI at baseline was not included.
“However once we know a person’s BMI at baseline (in their 20s), the added value of genetics, fitness or physical activity were all relatively small. If a person’s BMI history over time is known, the added value was even smaller. The main implication here is that for most adults, simply calculating a BMI using a standard scale and tape measure is probably sufficient, especially if these are tracked over time. Genetic risk scores that exist today do not add much to this,” Dr. Murthy told MEAWW.
He says, “There's been a lot of attention to the idea of using genetic information to understand your risk of obesity or being overweight, and for potential drug development to address those genetic risks. We wanted to understand how, if at all, genetic data would add to the information already routinely available in the clinic. It turns out, our standard clinical exam, including an assessment of BMI, actually has vastly more information to help guide patient care.”
The team used a modern polygenic risk score -- a composite measure of genetic risk of obesity -- to calculate the genetic risk of obesity for each person in their subset of the CARDIA study and compare it to the measurements taken during the 25 years of the study.
The polygenic risk score was also more effective at predicting future BMI in the 1,608 white individuals than the 909 black individuals, shows analysis.
According to the researchers, the data serve as a reminder that human genetics might be interesting in large population studies, but caution is needed toward incorporating them when providing clinical care and advice to patients.
However, Dr. Murthy acknowledges that clinicians are seeing more and more patients who have already purchased a genetic report from a direct-to-consumer company and want to go over it with their doctor. The researchers say it is important for clinicians to be aware of the strengths and limitations of those direct-to-consumer products.
Dr. Murthy adds the good news is that calculating your BMI, which is a useful marker for the majority of people who are not elite athletes, is significantly more affordable than purchasing a genetic test.
“Ultimately, while genetic risk may be most important in those individuals with rare inherited causes of obesity, for the majority of the population at risk for becoming obese, universal recommendations like healthy eating and remaining active are important and should be reviewed regularly with your personal physician," says senior author Dr. Ravi Shah from the Massachusetts General Hospital.