Health Corner: How exactly does obesity cause cancer?/Story: The Weather Girls

Health Corner: How exactly does obesity cause cancer? Three leading theories ‘Love handles’, ‘muffin top’, ‘beer belly’, ‘extra padding’, ‘cuddly bits’, ‘winter insulation’… We all have names for the squishy bits we keep meaning to lose – but apart from not fitting into our favourite jeans, carrying too much weight isn’t actually doing any harm, is it? Unfortunately, it is. And we’ve written several posts about the link between being overweight or obese and several types of cancer (here’s the most recent). But despite efforts to raise the profile of the link, public awareness remains stubbornly low – only around one in 10 people name being overweight as a factor when asked what things they think affect a person’s chance of developing cancer. This is an urgent problem: the world is slowly drifting into an obesity crisis, with the condition already linked to nearly 500,000 cancer cases worldwide every year. According to recent reports, public health experts predict that – shockingly – in the US obesity will soon overtake tobacco as the leading preventable cause of cancer – and the UK might one day follow suit. So it’s clear that those spare pounds aren’t a mere overflow car park for excess doughnuts. But that raises a crucial question: how exactly does fat increase our risk of cancer? While there are several plausible explanations, it’s an answer that researchers are still working hard to figure out. But first… just what is fat? Fat isn’t just padding: it’s like another organ Fat (also known as adipose tissue) has two main roles in the body. Primarily it exists to store calories in the form of chemicals called lipids, which – when food was scarce would serve as a back-up energy store to keep us going. But nowadays many people consume more calories than they use up, leading to more of us becoming overweight or obese. But the fat in your body also has a secondary function – it’s essentially a huge gland, sending out a constant stream of biological information and instructions that affect the rest of your body. This helps control processes like growth, metabolism and reproductive cycles. But because of their ability to turn biological processes on and off, the signals produced by fat have a darker side when it comes to cancer. This is especially true when people become overweight or obese – the point at which excess fat has a negative impact on health. Here are the three leading theories about how excess fat might lead to cancer, and the scientific evidence behind each one. the long and short of it There’s not a shadow of doubt that obesity is linked to cancer, but unravelling the biological reasons why is proving complicated. Being obese affects lots of different aspects of our physiology – hormones, growth signals, and inflammation. It also affects different people in different ways; for example, not everyone who is obese will have abnormal metabolism or chronic inflammation. To make matters more complicated still, oestrogen, insulin, and inflammation are a convoluted tapestry of interwoven threads. None of them in isolation directly causes cancer, but in obesity they knit together to form a lethal fabric – dampening the delicate systems that balance our bodies with disastrous consequences. And while it’s not simple to understand how the threads weave into the overall picture, researchers know that there’s potentially an opportunity to treat, or even prevent, cancer by developing drugs that override signals made by fat cells. For example, both metformin (a diabetes drug that affects insulin levels) and aspirin (which dampens down inflammation) are under investigation as possible anti-cancer drugs. We’ve focussed on cancer here, but of course that’s only part of the story. Obesity is a leading cause of death from other serious diseases too – diabetes, heart disease and stroke to name a few. So we urgently need to tackle the obesity crisis head on. And you’ll be hearing more about how over the coming months. As more people become overweight or obese (many without even realising it), the number of people dying from related diseases is rocketing. It’s not something we can afford to ignore. Emma https://scienceblog.cancerresearchuk.org/2015/11/25/how-exactly-does-obesity-cause-cancer/ Story: The Weather Girls. By Aki