The analysis of 12 large studies found significant reductions in breast, endometrial and colorectal cancers in particular among people who consistently followed cancer-prevention lifestyle guidelines compared to those who didn't.
"What is most interesting to me is how much cancer can be reduced by our lifestyle behaviors," said lead author Lindsay N. Kohler of the University of Arizona Mel and Enid Zuckerman College of Public Health in Tucson.
We already knew that making healthy choices reduces cancer risk, but "most of us don't follow all the guidelines like we should," Kohler told Reuters Health by email.
Nearly 1.7 million new cancer diagnoses and 600,000 deaths from cancer are expected in the U.S. this year, the study team writes in Cancer Epidemiology, Biomarkers and Prevention.
Recent studies have suggested that 20 percent of U.S. cancers may be caused by unhealthy lifestyle, including physical inactivity, poor diet, excess alcohol consumption and unhealthy body weight, the authors write. That shoots up to two thirds of cancers if tobacco use is added in.
To see if a healthy lifestyle helps to stave off cancer in general, the researchers looked at studies published in the last decade that followed large number of people over time. Some studies followed up to half a million men and women.
All the studies looked at whether and how consistently people adhered to lifestyle guidelines from the American Cancer Society or World Cancer Research Fund/American Institute for Cancer Research. Both organizations emphasize making healthy diet choices, such as eating a mostly plant-based diet with little or no meat, moderate alcohol consumption, staying active and maintaining a healthy body weight.
Overall, participants in the 12 studies who followed these guidelines were 10 to 45 percent less likely to be diagnosed with any cancer and up to 61 percent less likely to die of cancer, compared to people who adhered least to the lifestyle guidelines.
The incidence of breast, endometrial and colorectal cancers were in some cases halved for those who followed guidelines, depending on the study.
"Breast, endometrial, and colorectal cancer are all considered obesity-related cancers by the American Cancer Society," Kohler said. "The guidelines specifically include 'maintaining a healthy weight' as well as other recommendations for healthy eating and being physically active."
There was no association between guideline adherence and ovarian or prostate cancer, researchers found. Links between guidelines and lung cancer incidence varied by study, which made it impossible to summarize cancer risk reductions or draw conclusions about causality, the study team writes.
The populations in these studies couldn't be directly compared, so there is no pooled estimate of cancer incidences that could be avoided if everyone followed prevention guidelines, Kohler noted.
People may feel they don't have the time to exercise or the money to eat well, she said.
"However, a few changes can make big impacts," she said. "Following even some of these guidelines will lead to healthier overall lives and in turn reduce the risk for many major diseases."