People with low BMI aren’t more active, they are just less hungry and ‘run hotter’

To date most research on obesity has focused on studying those with a high body mass index (BMI), but a research group in China is taking a different approach. In a study published July 14 in the journal Cell Metabolism, the scientists looked at individuals with a very low BMI. Their findings reveal that these individuals are actually considerably less active than people with a BMI in the normal range, contrary to speculation that they have a metabolism that makes them naturally more active. Additionally, they eat less food than those with a normal BMI.

“We expected to find that these people are really active and to have high activity metabolic rates matched by high food intakes,” says corresponding author John Speakman, a professor at the Shenzhen Institutes of Advanced Technology in China and the University of Aberdeen in the UK. “It turns out that something rather different is going on. They had lower food intakes and lower activity, as well as surprisingly higher-than-expected resting metabolic rates linked to elevated levels of their thyroid hormones.”