“Frying meat on a gas hob may increase your risk of cancer,” according to the Daily Mail.
This news story is based on research that attempted to estimate the concentrations of potentially harmful chemicals that professional chefs are exposed to from the fumes of cooking steak.
This research looked at the gases produced by frying and not how breathing these fumes affected health or cancer risk. While the researchers found that certain harmful chemicals were produced, these were well within the established limits of safe environmental exposure. Although the chemicals found in these fumes may be carcinogenic in high concentrations, this study alone does not provide sufficient evidence to prove that fumes from cooking steak increase the risk of cancer in humans.
Where did the story come from?
This study was carried out by Dr Ann Kristin Sjaastad and colleagues at the Norwegian University of Science and Technology. The study was funded by the Norwegian Foundation for Health and Rehabilitation and published in the peer-reviewed journal Occupational and Environmental Medicine.
Although The Daily Telegraph and the Daily Mail stated that the amounts of the chemicals produced during cooking were within safety limits, this fact was not adequately emphasised in their reports and their coverage tended to sensationalise the story. This research looked at the chemical composition of cooking fumes. It did not look at the health consequences of exposure to the chemicals produced by cooking, as could be assumed from reading the media reports.
What kind of research was this?
This was a laboratory study looking at the chemicals found in the fumes from cooking steak. The researchers wanted to see if the fumes contained any harmful chemicals and what concentrations of these chemicals a cook would be likely to inhale.
The researchers say that previous research has shown that some chemicals found in cooking fumes can have effects on cells in culture, suggesting that they may be carcinogenic. The chemicals that they were particularly interested in were polycyclic aromatic hydrocarbons (PAH), which have been found in the fumes from different types of cooking oil.
The researchers explain that the International Agency for Research on Cancer (IARC) has recently classified the fumes from high-temperature frying as ‘probably’ cancer-causing to humans. They also highlight the results of a 1986 study that reported an increased risk of respiratory tract cancer in cooks and bakers. The researchers say that although there is “limited evidence” from studies in humans that emissions from high-temperature frying are carcinogenic, animal experiments have provided “sufficient evidence” to suggest that there is a link.
What did the research involve?
The researchers cooked 400g beefsteaks in either margarine or soya bean oil. The margarine used contained soya bean oil, rapeseed oil, coconut oil, palm oil and vitamins A and D. The first steak was cooked for 15 minutes, and after a 25-minute break the next steak was fried. The researchers repeated the process five times. Steaks were either cooked on a gas or electric hob.
The kitchen had an area of 19 square metres and was fitted with an extractor hood. Air samples were taken by drawing air into a sampling tube with a fixed flow rate that was attached to the shoulder of the person frying the steak. This experimental process was designed to mimic the exposure a chef would regularly experience in a restaurant kitchen, and not the type of exposure experienced in a home kitchen.
What were the basic results?
The researchers could only detect one type of PAH, a chemical called naphthalene. Naphthalene is commonly known as the primary ingredient of traditional mothballs. The concentrations of naphthalene in cooking fumes were 0.15 to 0.27 millionths of a gram per square metre. The researchers reported that the environmental exposure limit for PAHs in Norway is 40 millionths of a gram per square metre.
The researchers found that there were also various types of other chemicals called alkanals and alkanels in the fumes. These varied in concentration depending on whether the beef was cooked on an electric or a gas stove, with a greater amount generally found in the cooking fumes of steak cooked on a gas stove. They did not report if the two stoves cooked the meat at different temperatures. They also found that cooking on a gas stove produced a greater number of ultrafine particles in the air than cooking on an electric stove.
How did the researchers interpret the results?
The researchers concluded that the measured levels of total particles and PAHs that were likely to have been breathed in by the cooks were well below the occupational exposure limits set in Norway. They say that there are no defined limits for alkanals and alkanels.
This research looked at the chemical composition of cooking fumes produced when cooking steaks. The researchers set up their laboratory so that they could mimic the environment and length of exposure that a professional chef would regularly experience in a restaurant kitchen, and not a household setting. As such it should be regarded as preliminary laboratory research, which will need to be judged in the context of other studies looking directly at how these fumes affect health.
Although this study showed that some potentially dangerous chemicals were generated, these were well within the safe limits of exposure. Other chemicals produced have no established safe level. This will need to be examined through additional research.
The differences that the researchers observed in the chemicals produced when cooking on a gas compared to an electric stove are likely to be due to the different temperatures at which the steak was cooked. A limitation of the study was that these temperatures were not measured.
This study did not directly measure the health effects of cooking fumes, and overall it does not provide evidence that exposure to the fumes from cooking steak is bad for your health.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Daily Telegraph, 18 February 2010
Daily Mail, 18 February 2010
Links to the science
Occupational and Environmental Medicine; Published online February 17 2010