From doughnuts to French fries, eating deep fried food at least once a week is linked to a raised risk for prostate cancer, according to a new US study. The researchers did not investigate why the link exists, but suggest it could be because deep frying releases potentially cancer-causing compounds in the cooking oil or fat.

The researchers, from the Public Health Sciences Division of the Fred Hutchinson Cancer Research Center in Seattle, write about their findings in the 17 January online issue of The Prostate.

Previous studies have already shown links between prostate cancer and foods heated to high temperatures, such as grilled meats, but the authors believe theirs is the first to examine potential links with deep-fried foods.

Corresponding author Janet L. Stanford, co-director of the Hutchinson Center’s Program in Prostate Cancer Research, says in a statement released this week:

“The link between prostate cancer and select deep-fried foods appeared to be limited to the highest level of consumption – defined in our study as more than once a week – which suggests that regular consumption of deep-fried foods confers particular risk for developing prostate cancer.”

There is already evidence that eating deep-fried foods is linked to other cancers, namely breast, lung, pancreatic, head and neck, and esophageal cancers.

For their study, Stanford and colleagues examined data on 1,549 men diagnosed with prostate cancer and 1,492 age-matched healthy men living in the Seattle area.

The men, who were Caucasian and African-American, were aged between 35 and 74 years, and had taken part in two population-based case-control studies where they had filled in dietary questionnaires that included questions about how often they ate certain deep-fried foods.

The researchers found that men who ate French fries, fried chicken, fried fish and/or doughnuts at least once a week had a raised risk for prostate cancer of between 30 and 37%.

They also found men who ate these foods as often as this had a slightly higher risk of the more aggressive form of the disease.

Even when other factors that might affect the risk were taken into account, such as age, family history of prostate cancer, race, body mass index, and PSA screening history, the links stayed the same.

While she and her colleagues did not look at what might be behind the link, and their study did not prove that it’s the eating of deep-fried food that leads to higher risk for prostate cancer, Stanford suggests it might have something to do with what happens to the food when it is deep-fried.

At temperatures high enough for deep frying, potentially carcinogenic compounds can start to form in the food.

These toxic compounds, which increase as the oil is re-used and re-heated, include acrylamide, heterocyclic amines, polycyclic aromatic hydrocarbons, aldehyde and acrolein.

Acrylamide is found in carbohydrate-rich foods such as French fries; heterocyclic amines and polycyclic aromatic hydrocarbons form in meat when it reaches high temperatures; aldehyde is an organic compound found in perfume; and acrolein is a chemical present in herbicides.

Deep-fried foods are also known to contain among the highest levels of advanced glycation endproducts (AGEs), a group of compounds linked to chronic inflammation and oxidative stress, conditions that are associated with cancer.

A chicken breast that is deep-fried for about 20 minutes will have about 9 times more AGEs than one that is boiled for an hour, say the researchers.

The authors suggest the link between prostate cancer and deep-fried food could be an indication of a link between the disease and fast food consumption, since in the US most deep-fried food is eaten outside the home.

Funds from the National Cancer Institute and Fred Hutchinson Cancer Research Center paid for the research.

A study published in the American Chemical Society’s Journal of Agricultural and Food Chemistry in 2012 describes how the process for preparing French fries for fast food outlets can influence the formation of acrylamide, and suggests ways levels of the compound can be reduced.

Written by Catharine Paddock PhD