Researchers estimate that 59% of endometrial cancer cases about 29 500 every year in the United States could be prevented if women exercised at least 30 minutes a day and avoided excess body fat.
The report was published on 10 September by the American Institute for Cancer Research (AICR) and World Cancer Research Fund International.
"Body fat can produce hormones that promote cancer development," said Alice Bender, nutrition communications manager for AICR. "We also know that body fat is linked to chronic inflammation, which produces an environment that encourages cancer development."
The study also uncovered some diet choices that can raise or lower a woman's risk of endometrial cancer, which is cancer of the lining of the uterus.
Drinking one cup of coffee a day can reduce a woman's risk of endometrial cancer by 7%, whether it is caffeinated or decaf, the research suggested.
On the other hand, eating lots of high-glycemic-index foods, such as sugary items and processed grains, increases cancer risk. The risk goes up 15% for every 50 units of glycaemic "load", the study found.
All these factors influence hormones such as oestrogen and insulin that are believed to be at the root of endometrial cancer, the report concluded.
Endometrial cancer is the most common cancer of the female reproductive system. About 49 600 new cases of endometrial cancer occur each year in the United States, more than ovarian cancer and cervical cancer combined, according to the AICR.
Most cases of endometrial cancer are diagnosed in women over age 60. There is no reliable screening system to detect the disease.
The new review is part of an ongoing WCRF/AICR project, in which the two groups are collaborating to update their recommendations for cancer prevention based on the most up-to-date scientific evidence. Previous reports have updated recommendations for pancreatic, breast and colorectal cancers.
The panel's findings are "very consistent with our research with respect to obesity and physical activity," said Mia Gaudet, director of genetic epidemiology for the American Cancer Society.
"Endometrial cancer has one of the strongest associations with obesity of all the cancers we know that are associated with obesity," Gaudet said.
Hormonal changes associated with obesity promote endometrial cancer, said review panel member Dr Elisa Bandera, an associate professor of epidemiology at Rutgers Cancer Institute of New Jersey.
"Endometrial cancer is a disease mostly caused by excessive and prolonged stimulation of the endometrium – the lining of the uterus – by oestrogens, unopposed by the hormone progesterone," Bandera said. "Obesity is associated with increased oestrogen production by the adipose [fat] tissue in postmenopausal women, and is associated with increased insulin and insulin resistance as well as chronic inflammation. All of these factors affect the cells in the endometrium."
At the same time, physical exercise has protective benefits that extend beyond maintaining a healthy weight.
"Regular physical activity has been shown to decrease oestrogen and insulin levels," Bandera said. Exercise also strengthens the immune system and helps maintain a healthy digestive system.
Coffee likely reduces cancer risk because it contains powerful antioxidants like chlorogenic acid. These antioxidants can prevent DNA damage, improve insulin sensitivity and inhibit glucose absorption in the intestine, all of which could reduce risk, Bandera and the other experts on the panel concluded.
But by spiking blood sugar levels, high-glycaemic foods contribute to cancer risk. They flood the bloodstream with glucose and insulin, AICR's Bender said.
"Again, it's creating this environment that can lead to cancer development," she said. "Metabolic havoc, is what I like to say."
However, Bender cautioned against taking the evidence surrounding high-glycaemic foods too far, noting that some very unhealthy foods have a low glycaemic load.
"You can't just say I'm going to choose foods that are low in glycaemic load and that will be a healthy diet. Pure butter isn't something that we would recommend people eat all the time," she said. "We recommend a healthy, well-balanced diet with plenty of fruits and vegetables."
To learn more about endometrial cancer, visit the American Cancer Society.