Dr Simon Cork (Anglia Ruskin University, UK) explores the causes and associated risks of obesity. Transcript: People with obesity are often seen as lacking willpower. And since it became clear that being overweight is a big COVID-19 risk factor, there've been lots of calls for everyone to lose a bit of weight. But isn't that easy? Is obesity a choice? In short, no. The picture is much more complex than we tend to think. Studies show that between 50 and 70% of our body weight is down to our genes. To put that into context, about 80 to 90% of our height is down to genetics. And we wouldn't say that someone is tall because of what they eat. It's the result of hundreds of different genes, each contributing in a small way. Some might affect how hungry you feel, for example, by tweaking the sensitivity to the hormones that make you feel full. Another might limit the reward hormones that are released when you eat, meaning you need to eat more to feel satisfied. Experiments in animals have also shown that being overweight causes physiological changes that can compound these effects. And losing weight causes brain circuits to drive behaviour and metabolic changes that actively keep weight high. So does that mean that people with obesity are stuck and there's no point in exercising or changing our diets? No, but we should think about weight in a different way. It's about health, not aesthetics. And weight management is not the same for everyone. A 5% loss of body weight might not have a huge effect on what you see in the mirror, but can have significant health benefits. For example, in women, it can reduce the risk of developing breast cancer by 12%. It can also reduce blood pressure by the same amount as some antihypertensive medications. The motivation to lose a little weight for better health outcomes might be easier to sustain than those demoralizing goals based on your trouser size. The science tells us that diet and exercise will only lead to modest weight loss for most so the government can't just rely on a message of exercising more. Complex problems need nuanced solutions, and ultimately, changing the environment we're surrounded by is just as important. Thanks for watching. Follow The Physiological Society for more videos like this.