A diet high in starchy foods such as potatoes, rice and white bread may increase the risk of pancreatic cancer in women who are overweight and sedentary, according to a new study by Dana-Farber Cancer Institute, Brigham and Women's Hospital and Harvard School of Public Health researchers.
The study suggests that excess insulin - a substance used by the body to process the sugar in foods - can promote the development of pancreatic cancer. Findings are published in the 4 September issue of the Journal of the National Cancer Institute.
Nearly 30,000 men and women in the United States are diagnosed with pancreatic cancer each year, and an equal number die from it. Pancreatic cancer typically is highly aggressive and is one of the least curable malignancies. Only four per cent of the people with pancreatic cancer are alive five years after diagnosis.
"Our findings add to the growing body of evidence that suggests that insulin may have a role in the development of pancreatic cancer," explained senior author Dr Charles Fuchs of Dana-Farber. "Further research is needed, however, to track the connection in more detail."
Earlier laboratory studies have demonstrated that insulin encourages the growth of pancreatic cancer cells. Other studies have shown that people who are obese, physically inactive or have adult-onset diabetes mellitus tend to be "insulin resistant," causing them to produce larger-than-normal amounts of insulin to compensate and putting themselves at greater risk for pancreatic cancer.
The new study explored whether women whose diets are heavy in foods that increase insulin production are likewise at elevated risk for pancreatic cancer.
"Historically, cigarette smoking had been the only proven risk factor for developing pancreatic cancer," said the study's lead author, Dominique Michaud, ScD, of the National Cancer Institute, who initiated the research while at Harvard School of Public Health.
"We're working to determine whether there are dietary or behavioural risk factors - ones that can be modified. At the same time, we hope to learn more about the basic biology of the disease."
The researchers reasoned that if insulin fuels the growth of pancreatic cancer, then foods that prompt the body to produce large amounts of insulin should be associated with a greater occurrence of the disease. Knowing that the body uses insulin to burn sugar, the researchers focused on foods that raise blood levels of glucose, a sugar that is a main energy source for cells.
Data for the study came from the Nurses' Health Study, a project at Brigham and Women's Hospital that tracks health information on female nurses across the country. The researchers reviewed the dietary records of nearly 89,000 nurses to measure their intake of sucrose (the type of sugar in sweets), fructose (the sugar in fruit juices and honey) and carbohydrates.
The researchers also calculated the amount of glucose-stimulating foods (known as the "glycemic load") every study participant consumed. Each type of food increases glucose levels by a different amount. The ability of carbohydrate-containing foods to boost glucose - and thereby insulin - levels is known as the "glycemic index." Starchy foods such as potatoes, white rice, and white or rye bread (all staples of the Western diet) have high glycemic indexes.
The researchers found that women who were significantly overweight and physically inactive (and whose levels of glucose and insulin were therefore already above normal) were more than two-and-a-half times more likely to develop pancreatic cancer if they had a high glycemic load than if they had a low glycemic load. Interestingly, a high glycemic load did not increase pancreatic cancer risk among women who were lean and physically fit.
An analysis of pancreatic cancer rates in all of the women in the study showed that women who had high glycemic loads were 53 per cent more likely to develop pancreatic cancer than were those with low loads. Women who consumed large amounts of fructose had a 57 per cent greater risk of pancreatic cancer.
The researchers noted that neither of these trends reached the level of statistical significance due to the limited number of cancer cases in each category.
Although the study involved only women, the researchers point out that is no reason to think that the findings do not apply equally to men.
"The take-home message for women who are overweight and sedentary is that a diet high in starchy foods may increase their risk of pancreatic cancer," said Fuchs. "Substituting less starchy vegetables such as broccoli for potatoes and rice and snacking on fruit are some simple steps that they can take to reduce this potentially serious health risk."