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Diet and lifestyle

The same genes determine fitness and fatness

Being fit is healthy and being fat is not. No news there. Nevertheless, science shows that genes, and sometimes even the same genes, can predict both fitness and fatness. New Danish research suggests that our percentage of body fat – and not our muscle mass – mostly determines whether we can become fit

Christmas in Denmark can be a happy time, but like the snow we fall for Christmas food and sweets. Then, in January, people diet and go running. A perennial discussion point, also in science, is whether fitness or belly fat is more important for long-term health. Now Danish researchers have shown that they are the same thing in part – at least genetically.

“We already knew that being predisposed to obesity is associated with 12 specific areas of our genes and that being fit is also linked to our genes. What is new about our study is that we are the first to show a direct genetic link between body fat percentage and fitness. So if you are genetically predisposed to obesity, you are probably also predisposed to being less fit,” explains Theresia M. Schnurr, the lead author of the study and a PhD student at the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen.

Fat is the deciding factor

The researchers thoroughly analysed the height, weight and body fat percentage of the 230 members of 55 families in Denmark. The researchers measured the maximal oxygen uptake of all family members to determine their physical fitness. Lastly, all the data were examined to determine whether genes, body fat percentage and physical fitness were correlated.

“We found very significant genetic factors linked to both the propensity to become obese and general physical fitness. The results suggested that genetics can explain at least half the population’s variation in body mass index, body fat percentage and physical condition, with environmental or other factors accounting for the other half.”

Nevertheless, the researchers were surprised that the participants’ body mass index, physical fitness and genes were not associated.

“We had assumed that the muscle mass of the participants would be associated with their physical fitness, but it was not. In contrast, their body fat percentage, physical fitness and genes were very clearly correlated.”

Personalizing future treatments

How fitness and fatness interact in the human body is not yet known with certainty. However, the Danish researchers have theories on how fatty tissue can influence physical fitness.

“We had seen how highly trained athletes such as cyclist Jan Ullrich had problems keeping their weight low and thereby staying fit. Shedding the extra weight immediately enabled him to cycle faster. Our theory is that fatty tissue expresses several substances and factors that affect the body’s physiology by directly influencing the uptake of oxygen,” explains associate professor Tuomas Oskari Kilpeläinen.

Although the researchers still have far to go to prove their theory, the new study is an important step. Even though much time will pass before this knowledge can be applied, The resarchers sees huge potential.

“If we can find out how fitness and fatness are genetically linked, we can also screen to determine which people are predisposed to being obese and thereby help them early. Each person’s individual genetic profile will presumably also be able to determine the ideal combination of diet and physical activity to ensure a good, healthy and long life."

Genetic correlation between body fat percentage and cardiorespiratory fitness suggests common genetic etiology” was published in PLoS One. In 2010, the Novo Nordisk Foundation awarded a grant of DKK 885 million to the University of Copenhagen to establish the Novo Nordisk Foundation Center for Basic Metabolic Research. Theresia Maria Schnurr is employed there as a PhD student and Tuomas Oskari Kilpeläinen as associate professor.

Theresia Maria Schnurr
PhD Student
Section for Metabolic Genetics Universitetsparken 1, 1st floor, DIKU, 2100 Copenhagen Ø, DIKU
Tuomas Oskari Kilpeläinen
Associate Professor
Tuomas Kilpeläinen earned his PhD at the University of Kuopio, Finland, and from 2009 to 2011 he was a post-doctoral fellow at the MRC Epidemiology Unit, University of Cambridge. In 2012 he became an assistant professor, and in 2016 an associate professor, at the Section of Metabolic Genetics of the Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen. Since 2015, he is also an adjunct assistant professor at the Icahn School of Medicine at Mount Sinai, New York. Tuomas’s main research interest is the identification of genetic variants contributing to the risk of obesity and type 2 diabetes and the study of how lifestyle modifies the genetic effects. Thereby he has coordinated or been actively involved in the work of a number of consortia of genome-wide association studies, and a major part of his work has focused on the identification of gene x lifestyle interactions in large-scale meta-analyses of genetic studies.