Professor Fred Saad, a cancer specialist at the University of Montreal, says that exercise and weight loss increase survival rates, and that high-intensity exercise, spurred on by a trainer, is more effective than exercising alone.
His comments come as experts launch the world’s biggest trial looking at how weight loss may stop the disease coming back.
It is already known that being overweight contributes to the development of 11 types of cancer but researchers believe it also affects how some people respond to treatment and the risk of recurrence.
Evidence presented at the American Society of Clinical Oncology (ASCO) conference in Chicago yesterday shows that being overweight results in poorer outcomes, while exercise appears to show promise in helping people beat the disease.
Dr Jennifer Ligibel, assistant professor of medicine at Harvard Medical School, is launching a major trial looking at whether losing weight can cut the chance of breast cancer coming back.
Although previous observational studies have found a link, hers will be the first randomised controlled trial with a specific aim of seeing how weight loss affects cancer.
The new trial will enrol 3,200 women from the US and Canada who are overweight and obese with a body mass index of at least 27.
They will be randomly split into two groups, with the intervention arm receiving weight-loss advice to lose 10 per cent of their body weight alongside an exercise programme, for two years.
Dr Ligibel said that of 100 women, around 23 would normally be expected to have a recurrence of cancer, but this should drop to 19 in the weight-loss group.
Women on the diet will have around 1,200 to 1,500 calories per day and exercise for about 150 minutes a week for the first six months, increasing to 250 minutes where possible.
She said brisk walks would count as exercise, adding: “It’s a very accessible form of exercise. It doesn’t cost anything. You just need a pair of shoes.
“This will be the largest study that’s ever tested the impact of weight loss on cancer – any form of cancer.”
Another study is also being launched that will look at the effect of exercise on the risk of disease coming back in men with prostate cancer.
Professor Melinda Irwin, of Yale Cancer Centre, who is involved in eight studies concerning exercise and cancer, says she has found a “strong connection between exercise after diagnosis and mortality afterwards”.
Women with breast cancer who have never been active before can benefit from exercise, she believes, adding that she is “in the camp that says this association is causal and reversible”.