Simple precautions can reduce carcinogens in the kitchen and on the food table, writes Mia Malan.
There is strong evidence that many cancers are caused specifically by what we eat and drink. How we prepare our food, how much of it we eat and how we eat it frequently determines the risk of developing cancer. No one knows these factors better than Carl Albrecht, head researcher at the Cancer Association of South Africa (Cansa). In the first of a two-part series, the Mail & Guardian spoke to him about 10 causes of cancer in the kitchen.
Most processed meat, including polony, sandwich meat, bacon and vienna sausages, contains a cancer-causing ingredient called sodium nitrite. Sodium nitrite helps to prevent germs from growing in the meat and also gives it a visually appealing red colour.
When you eat sodium nitrite, nitrosamines form in your body, promoting the growth of a variety of cancers, including pancreatic, colon, bladder, stomach and brain cancer.
A recent Cansa survey of major South African grocery shops could not find a single piece of processed meat that did not contain sodium nitrite. Processed meat is unfortunately also the cheapest and often the only meat that many South Africans can afford. Limit your intake of processed meat, if you can.
It is not only cigarette smoke that causes cancer—any type of smoke can. Smoke, including braai smoke, contains dangerous chemical compounds called polyaromatic hydrocarbons (PAHs). Many are carcinogens, in other words, they cause cancer, particularly one called benz(a)pyrene. It binds to your DNA and “knocks out” a watchdog gene, P53, which protects against cancer.
A study done on female restaurant cooks in Hong Kong, whose jobs entailed pan-frying meat and vegetables in relatively small kitchens, indicated that they had significantly higher rates of cancer of the upper respiratory tract, for example, nasal, oral or throat cancers. Research revealed that the cancers were caused by the fumes produced by the intensive frying. Open your kitchen windows so that smoke from cooking can escape. And get out if you find yourself in the middle of a kitchen full of smoke.
Smoked meat is also closely linked to cancer. Many years ago people smoked meat to better preserve it because they did not have freezers. If you have access to electricity and a freezer, avoid smoked meat.
Potato chips and reused oil
When potatoes are deep fried to make potato chips, a cancer-causing chemical called acrylamide is released. Acrylamide is associated with kidney, post-menopausal and endometrial cancers.
Research studies show that an ordinary bag of potato chips may contain up to 500 times more acrylamide than the top level allowed in drinking water, one microgram per litre, by the World Health Organisation. Research commissioned by Cansa revealed that chips sold in South Africa contained between one and three milligrams acrylamide per kilogram. Acrylamide is used industrially to manufacture dyes, paper and fabric, among other things.
It is not added by manufacturers; the chemical forms naturally when potatoes are heated up in oil at a high enough temperature and for long enough. Reusing oil in which potatoes have been cooked can therefore also be dangerous, because the pieces of potato that stay behind will eventually become potato chips and form acrylamide. The question is: How much acrylamide do you need to consume before it causes cancer? According to Cansa, such information is not yet available in South Africa. It is therefore best to consume potato crisps moderately—maize or rice crisps are safer.
It is not safe to heat food or liquids in plastic containers or bottles in microwave ovens. When plastic is heated, it releases potentially cancer-causing plasticisers, which are used to give plastic its desired flexibility. One of the most commonly known chemicals released is bisphenol A, which has been linked in particular to breast cancer and obesity. Bisphenol A is used to make polycarbonate and baby bottles containing it were banned by the health department last year. But the substance is still legally used in certain baby toys and plastic kitchen products.
Storing or freezing food in plastic containers is safe, because it only becomes dangerous when the plastic is heated. It is safer to heat food in ceramic or glass containers. Limited data is available about the exact temperature at which plastic becomes dangerous, but studies have shown that 55 times more bisphenol A is released from bottles filled with hot water than from those with cold water.
As a general rule, avoid heating any plastic bottle. Boil water or milk in another container and then allow it to cool before pouring it into a plastic bottle.
Dioxins are a cancer-causing substance that often end up in animal fat. They are regularly released into the atmosphere—the burning of certain types of plastic and metals produces them.
Typically, factories that release dioxins as a by-product are situated outside urban areas—where animal farms are mostly located. Dioxins descend on the grass that cows and sheep in particular eat.
The animals consume the dioxins with the grass and the chemicals are then stored in their body fat. When we consume such animal fat, the dioxins end up in our own body fat where they can stay for weeks on end. The longer they stay there, the higher the chance they will cause damage; minute amounts can be carcinogenic.
Few dioxin tests have been done on local meat and it is best to limit your intake of animal fat, including those fatty pieces on biltong.
Mouldy peanut butter
Peanuts and peanut butter in grocery shops are safe. But, if you make your own peanut butter, as many people in the former Transkei do, you have to make sure that the peanuts do not get mouldy. Mouldy peanuts are a source of a food contaminant known as aflatoxins. Aflatoxins are produced by fungi that grow on certain crops, such as peanuts, and are closely linked to liver cancer.
About a decade ago an aid organisation provided many people living in the former Transkei with free hand mills so that they could grow and mill their own peanuts and make a living from it. Unfortunately, many of the peanuts became mouldy, exposing people to large amounts of aflatoxins.
It remains to be seen what the effect has been: according to Cansa, there could be a liver cancer epidemic in the region in future as people who ingested mouldy peanuts as children grow into adults.
Some South African provinces, such as Gauteng, have excellent quality drinking water. However, that of Potchefstroom in North West, for example, is problematic because gold mining has caused large amounts of uranium to leak into the Mooi River. According to Cansa, Potchefstroom’s drinking water is taken directly from the river.
When underground metals such as iron are exposed to oxygen or water, they release acids similar to those found in car batteries, which help to leach heavy metals out of the ore. Exposure to uranium is linked to lung and bone cancer.
The government’s safety standard for uranium in water is 70 micrograms per litre. But the World Health Organisation’s standard is much more stringent, 15 micrograms per litre, whereas countries such as Germany allow only two micrograms per litre of water for the production of baby food.
According to Albrecht, the local municipality claims Potchefstroom’s drinking water is safe because tests have shown that only one microgram per litre flows through the river on weekdays. But, he said, the municipality did not measure the uranium content of water over weekends, which was when mines often cleaned out their shafts and released significantly higher amounts of uranium into the water.
Cansa takes the situation so seriously that it plans to conduct studies on the teeth of residents of Potchefstroom to determine the level of uranium to which they have been exposed.
It is therefore recommended that people living in the town buy bottled water or install water filters at home. Note that boiling water in a kettle does not make it uranium-free because uranium sticks to kettles’ elements.
“It doesn’t help to drink clean water but then use unfiltered tap water to make coffee and tea or to cook with,” Albrecht said. “You need to use uranium-free water throughout.”
According to Cansa, South Africa has one of the highest colon cancer rates in the world and “braaied red meat is the chief culprit”. A Cansa document titled “Life is Beautiful” states that people who consume “more than 70g of braaied meat a week are at a significant risk of developing colon cancer”.
Braaied red meat, states the document, contains amino acids and iron that produce chemicals and change DNA when exposed to high temperatures, which may lead to cancer. As explained earlier, all smoke also contains PAHs, which cause cancer. PAHs are inhaled by the people next to the fire and also ingested because they stick to the meat as it is exposed to the open flames. If you eat pap (mealie meal) with your braaied meat, you can lower your chances of getting colon cancer, because pap releases anti-carcinogens in the colon that help to fight it. Try not to braai more than once a week.
About 10% of all cancers in men are linked to excessive alcohol intake, in other words, more than two standard drinks a day. In women 3% of cancers are associated with too much alcohol.
Studies show that alcohol disrupts the hormones glucagon and insulin, which regulate blood glucose levels. It also releases reproductive and growth hormones, which cause dysfunction. Excessive alcohol intake can cause cancer of the mouth, pharynx, liver, colon and oesophagus. In women, high intake is specifically linked to breast cancer.
Obesity causes about 15% of cancers, including colon, kidney, breast, endometrium (the lining of the uterus) and prostate cancer. Sugar does not directly cause cancer, but it is calorie-dense and can lead to obesity, which is linked to cancer.
Limit your intake of foods that have an energy content of more than 950kJ per 100g—it is almost always indicated on the food container.
Mia Malan works for the Discovery Health Journalism Centre at Rhodes University. Next week the focus is on foods that can reduce the risk of developing cancer.