Chris van Tulleken

EVE SIMMONS: It's a discussion that has raged for a decade and is at the forefront of our understanding of what makes us fat. On one hand, a group of diet scientists who claim that our ever-more sedentary lifestyles are to blame for our increasing obesity epidemics. According to them, inactivity is so detrimental to health, leading to weight gain that raises the risk of everything from heart disease and diabetes to multiple cancers, which is on par with nicotine. They say,'sitting is the latest smoking'. Exercise has absolutely nothing to do with it, according to other influential and well-respected experts. It's only what we eat that matters. Public health officials would be better off focusing on improving the quality of the British diet, according to these researchers, including the app and Zoe Diet's creators. Katherine Richards (right), 48, claims she exercises almost every day and is still obese. Is she proof you really can't outrun a bad diet?