You probably have that one friend who is tall and skinny. You know, the one that eats whatever he wants, doesn’t exercise, and drinks like he’s going to prison. But the funny thing is, he never puts on weight, his body mass index (BMI) is fine, and he is in relatively good shape. Conversely, you have another friend who is short and fat, but is always mindful of what he eats, exercises regularly, and only drinks sparingly. That guy never seems to be able to shed pounds, no matter how hard he tries. So, what gives? According to a new study, genetics may be the difference between these two people.

University of Queensland researchers found genetics may play a role in height and body mass differences between people who are from northern European countries and those from other European countries. Queensland Brain Institute researcher Dr. Matthew Robinson stated these findings could explain why people from northern European countries are usually taller and leaner than those from other European countries.

The study took into account the height and BMI of 9,416 people from 14 European countries and used data from genome-wide association studies, which test for common genetic variants in a large group of people to determine if any are associated with a specific trait. Robinson said genetic differences between certain countries could explain differences in height, but body mass index (BMI) was determined mostly by environmental factors, like diet. “[D]ifferences in diet, for example, are more important than genetics in creating differences in BMI among nations," Robinson said.

Though BMI may not be the most accurate representation of a person’s true healthy weight, Robinson found the gene that led to a person having a lower BMI was strongly associated with the genes that resulted in greater height. "Our findings give a genetic basis to the stereotype of Scandinavians as being tall and lean," Robinson said in a press release.

Professor Peter Visscher, who assisted with the research, said that the genetic differences were probably a result of natural selection based on height and BMI. "The research suggests that tall nations are genetically more likely to be slim," he said.

Twenty-four percent of the genetic differences in height and 8 percent of genetic differences in BMI could be blamed on the region people lived in, Robinson said. In turn, these genetic differences could also affect the population’s chances of developing certain diseases, such as dementia, diabetes, and heart disease. However, further research will be necessary before that can be determined.

Source: Robinson, M, Visscher, P, et al. Population genetic differentiation of height and body mass index across Europe. Nature Genetics. 2015.