Substantial weight gain over years raises the risk of obesity-related cancers in men by 50 percent and in women by almost 20 percent, according to new data presented at the National Cancer Research Institute's (NCRI) Cancer Conference in Liverpool, UK.

Researchers at The University of Manchester and The Health eResearch Centre looked at how weight gain over many years might impact on the risk of developing obesity-related cancers, focusing on changes in BMI in around 300,000 Americans between the ages go 18 to 65, with an average follow up of 15 years.

The results showed that men who went from a BMI of around 22 to 27 had a 50 percent increased risk of developing obesity-related cancer compared those who stayed within a healthy weight range. In men who went from being overweight to morbidly obese, the risk jumped 53 percent.

Women who went from a BMI of 23 to around 32, had a 17 percent increased risk in comparison to women whose weight remained healthy.

"This research shows how important it is to look at weight gain over a person's lifetime - to give a clearer picture of cancer risk through life compared to assessing someone's BMI at a single point," said Dr Hannah Lennon, lead author and researcher at Manchester university.

"This study could also be really useful in public health. It could help identify people who would benefit the most from taking action to control their weight before any health problems arise - including a cancer diagnosis," she added.

Dr Karen Kennedy, Director of the NCRI, said: "This study provides a deeper understanding of the health implications caused by the obesity epidemic. It helps paint the picture of how risk could accumulate over time for different people, and could provide health professionals with a means to asses an individual's risk."

Being overweight or obese is the second biggest preventable cause of cancer in the UK after smoking and contributes to around 18,100 cases of cancer every year.

"It's important that people are informed about ways to reduce their risk of cancer. And while there are no guarantees against the disease, keeping a healthy weight can help you stack the odds in your favour and has lots of other benefits too," stressed Sir Harpal Kumar, Cancer Research UK's chief executive.

The findings are particularly pertinent given that the obesity epidemic shows no sign of abating, while recent research from CR UK revealed that the majority - 75 percent - of people in the UK are unaware that there is a link between obesity and cancer, highlighting the huge challenge for public health and NHS services.