Much like the old saying goes, looks can be deceiving. Research out today shows that a substantial number of people with so-called “normal” body mass index still have health problems related to obesity. Scientists at the University of Southern California studied nationally representative data on Americans and found roughly a quarter of people with normal BMI and half of people with an overweight BMI still met the standard for obesity under a recently developed criteria. As a result, the researchers say, many of these people likely aren’t getting the optimal care they need. “Since most doctors are focused on BMI to screen for obesity-related conditions, this is a population that might not be getting enough attention for screening and treatment of obesity-related conditions,” lead study author Brian Lee, a hepatologist at USC’s Keck School of Medicine, told Gizmodo. Clinical obesity BMI is calculated using a person’s weight and height, with obesity classically defined as having a BMI of 30 and over. Lately, though, some doctors and patients have advocated for a more nuanced meaning. Since obesity is actually about having too much excess fat, they argue, simply relying on BMI can miss some skinnier people who would otherwise fit the bill. Likewise, people who are especially tall or muscular can be characterized as obese despite not having excess fat.