The fat in your genes might keep you out of those jeans

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The fat in your genes might keep you out of those jeans

First study of its kind finds 11 variations in genes that play a role in body shape and obesity of South Africans

Journalist

Wits University and US researchers have identified 11 genetic variations responsible for body composition and fat distribution in South Africans.
The results have just been published in the journal Nature.
Body composition refers to the amount of fat, water and muscle mass in the body and how it is distributed. Dr Zané Lombard, principal medical scientist in the division of human genetics, said: “An important aspect of this study is that it is the first study of its kind focused on a South African population. It is important to study all populations in the world because there might be different genes influencing these traits in different populations.”
Wits professor of human genetics Michele Ramsay, who co-authored the study, said that “only 3% of genomic research is currently conducted in Africans, yet African populations make up 17% of the global population and despite their unique genetic diversity they remain vastly understudied”.This means that if medicines or preventative tests based on genetics become available later, they will exclude Africans, unless genomic research on the continent intensifies.
Lombard said there are probably more than the 11 genetic variations that play a role in body composition in the group of South Africans. “We didn’t look at all known genes in the human genome, so there are likely to be more that we didn’t detect.”
The research was done as part of Wits student Venessa Sahibdeen’s PhD.
Ramsay said the genes that played a role in body shape and obesity were the same as those influencing the body composition of Europeans, but the genetic variations in the South African population differed. There is a difference between a gene and a genetic variation. The same genes in each person determine eye colour, but gene variations will determine whether a child is born with brown or green eyes.
There are about 100 genetic variations linked to body composition that have been identified globally, said Ramsay.Lombard said that understanding the genetic factors in weight gain and obesity does not let people off the hook when it comes to eating well. “The gene effects we detected have a small effect on body composition. Having these gene variants alone won’t mean you will be fat or thin and you will still need to exercise and eat a healthy diet to maintain a healthy weight.
“We look at these gene variants as risk factors rather than deterministic. Obesity is a complex disease and, although one of these gene variants might put you at risk of having a higher (body mass index), for instance, it won’t be the only factor that determines your BMI.”
Genes play a role in weight gain but diet can change the way genes act, said Ramsay.
“Our genes do influence our metabolism and the way we break down and store fat, and in turn our behaviour can influence the way in which our genes perform,” she said. 
The participants in the study are from Soweto and are part of the larger Birth To Twenty study. Researchers from the Wits Agincourt Unit followed them from birth in 1990 until at least 2010 to help scientists understand how genetics and lifestyle influence health.Some of the participants’ mothers also took part in the study. A total of 1,926 people’s genetic material was used. They all consented to their DNA being tested.
Other measurements included BMI, waist and hip circumference, waist-to-hip ratio,  total fat mass, total lean mass and percentage fat mass. The weight of each woman’s head was removed from the study since many had weaves or hairpieces, which significantly added to their weight.
Lombard said the importance of this type of study is that  “knowing which genetic variants put you at higher risk of becoming overweight [in the future] can be used to screen for candidates who are at particular risk for obesity and to target interventions to this group before they become overweight”.She added: “Knowing which genes influence body composition could also help us understand which metabolic/biological processes could be good targets for new anti-obesity drugs.”
The study report stated: “This current study offers a significant contribution to our current understanding of the role of genetic factors to body composition in an African population.”
Said Ramsay: “We still have much more to learn about the way in which genetic differences and our behaviour determine how fat we are and how this changes during different times in our lives.”

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