In this study, researchers estimated that the more weight gained, the higher the risk of cancer. Obesity is the biggest cause of cancer in the UK, after smoking. And with 2 in 3 UK adults either overweight or obese. But while it sounds logical that losing weight would reduce the risk. Most of this evidence comes from studies that have used body mass index (BMI) as a measure of body fat.

When studying people, separating those who lose weight intentionally from those who lose it because they're already ill can be tough. On top of that, losing weight and keeping it off is hard. But this hasn't stopped researchers from hunting for answers. And the good news is, research so far tells us that weight loss is beneficial when it comes to reducing cancer risk.

And the results suggest that the longer someone is overweight, the higher their risk. Based on this, losing weight (and keeping it off) means you stop accumulating more risk, and reduce your risk compared to what it would be if you gained more weight. So losing weight does help, both with cancer risk and your general health.

Weight loss through surgery

One of the most effective, although extreme, ways for people who are very overweight to lose weight is bariatric surgery. This covers a range of surgical techniques, such as stomach stapling or surgically bypassing large parts of the gut.

Because people lose a lot of weight after surgery, and keep most of it off, it's more likely researchers will find an effect on cancer risk if it's there. Results from studies post-surgery are mixed, but overall they suggest that people who undergo bariatric surgery do have a reduced risk of cancer compared to those who don't.

The strongest evidence so far is for women, but evidence is growing in men too. A study that combined the results of 6 others found a staggering 45% reduction in cancer risk among formerly obese people who had bariatric surgery. But when they split the results by gender, this finding only remained in women.

If you are overweight, you can reduce your risk by avoiding gaining more weight. And overall, all the research carried out so far suggests that an increased risk can start to fall with weight loss. But the fact remains that losing weight and keeping it off can be incredibly hard. So this must be supported by public health measures that make healthy choices easy for everyone, both to prevent weight gain.

Never gaining extra weight in the first place is still best for reducing cancer risk. But we know that's not possible for everyone and it doesn't help people who have already gained weight. So having evidence that weight loss could help is good news.