Obesity poses a major threat to public health. Between 1975 and 2016, the number of obese people, defined as those with a body mass (BMI) greater than 30 has tripled.Children are becoming more obese in the UK. Nearly a third of all children are either overweight or have obesity. Obesity can lead to many health problems, including diabetes, heart disease, and cancer.Recent research has shown that obesity can increase the likelihood of severe illness following COVID-19 infection.There are many factors that can lead to obesity. We now know one: genetics. Are scientists able to find a 'obesity genetic' or are the genetics more complex?Five experts in genetics and nutrition asked us to ask "Is there an "obesity" gene?" Here's what they had to say.What are our genetics for obesity?Researchers scan a lot of people's DNA in order to identify genes or variants of genes that are associated with obesity.Cornelie Nienaber-Rousseau is a nutrition expert from North-West University, South Africa. She says that large-scale genome-wide association (GWAS), studies have found multiple loci and genes associated with body mass index. Rarely, however, obesity can be caused by a specific syndrome that is due to a mutation of one gene.The function of genes that are associated with obesity or body mass index can vary. These genes are controlled by Dr Ivor Ebenezer (a University of Portsmouth expert in neuroscience), who says they "control the hormones and neurotransmitters and neuromodulators and enzymes involved with the regulation of energy intake and energy homeostasis."What genes are linked to obesity?It doesn't make sense, evolutionary speaking, that obesity is a result of genes passed down from one generation to the next.Dr Ebenezer says that when we look back at history to the time our hunter-gatherer ancestors roamed this earth, we see that early man ate mainly root vegetables (which contain high amounts of carbohydrate) while hunting animals for their proteins and fats. They were often hungry for a long time, sometimes for several days or even weeks. Those who survived were able store body fat in times of abundance to give energy during times when it was difficult. The majority of us inherit genes from our ancestors which predispose to accumulating body fat.These genes were vital for survival in times of food shortage, but they are now harmful to those who have easy access and don't need physical exertion.What are other factors that contribute to obesity?Genetics can play a role in obesity, but it's not the only factor. Dr Richard Edwards, a UNSW Sydney geneticist, says that obesity is a complex trait controlled by many genetic and environmental factors. It is easy to see the differences in obesity rates between modern and older generations. However, our genes have not changed much in this time.Our environment plays a significant role in obesity. Dr Ebenezer states that "obesity is caused by an increase in food intake and decreases in energy expenditure." Surprisingly, however, the environment can also influence our genes.Dr Edwards explains that the "biggest genetic factor" is not what genes you have but how they are expressed and controlled.Dr Ebenezer explained that epigenetic changes can be caused by environmental factors such as maternal starvation and high sugar foods. This can lead to obesity in the offspring.Other factors that can influence obesity are not well known. Dr Ebenezer explains that "recently, it was discovered that the gut microbiome plays a significant role in controlling hunger and satiety through modulating hormones and neurotransmitters."The bottom line: Genetics isn't the only factor that causes obesity. There are many factors.This article is based on five expert answers to the question: Is there a obesity gene?This expert response was published by Metafact.io, an independent fact-checking platform. Subscribe to their weekly newsletter.
