“[Your BMI] doesn’t tell you your percent body fat, how much muscle mass you have, what your lean body mass is, where the fat is distributed,” Dr. Eduardo Grunvald, program director at UC San Diego's Weight Management Program, says. “Two people with the exact same BMI might have very different health risks.”
There's a lot of other stuff going on inside your body
Obviously, weight plays a role in a person's health, but it's not exactly a black-and-white issue. Some people can be 50lbs overweight and still run a marathon, while others at a perfectly normal weight get winded walking up a flight of stairs. It’s best to leave an official assessment up to doctors, who can perform a series of tests to more directly gauge overall health.
“Tests that are very useful to convey [health] risks [include] blood sugar, HDL levels, and elevated triglycerides or LDL (bad cholesterol),” says Dr. Caroline Cederquist, founder of the diet delivery program BistroMD. Performing a hemoglobin A1C test is a good indicator of of how your body is using glucose, she adds, as is a fasting insulin test, both of which can show indications of pre-diabetes. Although these complications are commonly associated with lifestyle, some people are more genetically predisposed to high blood sugar or bad cholesterol, despite being a normal weight.