Cancer Research UK : Diet and cancer - acrylamide, artificial sweeteners, green tea, soy, tomatoes and vitamin supplements

Diet and cancer - acrylamide, artificial sweeteners, green tea, soy, tomatoes and vitamin supplements

Acrylamide, found in French fries, is unlikely to increase the risk of cancer.

Acrylamide

In 2002, a Swedish study reported that many foods contain high levels of a chemical called acrylamide. International public concern followed since acrylamide is known to cause cancer by damaging DNA. This substance is produced when starchy foods are heated to high temperatures, and is found in foods such as chips, crisps and some bread.

However, several recent studies in people found that the levels of acrylamide in food are far too low to cause cancer. Many studies found that acrylamide has no impact on the risk of several different cancers. Even food industry workers, who are exposed to twice as much acrylamide as other people, do not have higher rates of cancer. Many scientists now believe that the public scare about acrylamide was based on faulty data.

Artificial sweeteners

Artificial sweeteners are used in a wide variety of foods and drinks. Almost everyone in developed countries consumes them, whether they know it or not. Because of this, any potential cancer risks would be very far-reaching. But overall, studies on artificial sweeteners have found that they do not increase the risk of cancer.

Saccharin is one of the best studied of the artificial sweeteners. Some studies in the 80s found that it could cause bladder cancer in rats. Because of this, the Canadian government banned saccharin, and the American government warned that it could cause cancer. We now know that these effects were specific to rats and not relevant to humans. Bladder cancer risks are the same even in diabetics, who use sweeteners more frequently, and in people who lived through WWII, when saccharin use was high.

Aspartame, another type of sweetener, was also the subject of a cancer scare. This was because of an article linking it to rising brain cancer rates. This article had very little scientific basis and many later studies showed that aspartame, like saccharin, was safe for humans.

More recently, a large study found that aspartame could cause some cancers in rats. The European Food Safety Authority (EFSA) reviewed this study and found that it was significantly flawed. The EFSA’s detailed report sets out the facts clearly and concludes that aspartame does not increase the risk of cancer below the daily recommended level. Even people who consume a lot of sweetened foods take in well below this amount.

Research suggests that established sweeteners like saccharin and aspartame are safe for people. But more research needs to be done on the possible effects of recently introduced, new-generation sweeteners.

Green tea

Some studies have found that green tea could reduce the risk of many cancers including cancers of the breast, prostate, mouth, foodpipe, stomach and bowel. The most promising studies were done in Asian countries. Studies in Western countries have mostly found no effect on cancer risk. These differences may be because Asians drink large amounts of green tea while people in Western countries drink mainly black tea.

Green tea contains high levels of a group of chemicals called catechins. Because of the way it is prepared, green tea contains 3-10 times more catechins than black tea. Laboratory studies on cells have shown that catechins could block the growth of cancers. They prevent DNA damage by mopping up free radicals, blocking the growth of tumour cells and stopping the activation of cancer-causing chemicals.

We still need more evidence from large-scale studies and clinical trials to prove that green tea could help to prevent some cancers.

Soy

The soybean is a staple part of East Asian diets. Some studies have linked eating soy products, such as tofu, soymilk or miso, to reduced risks of breast, prostate and bowel cancer. Some studies have found that Asian people who eat more soy have lower risks of these cancers compared to Western people. But the differences in cancer risk between these groups may be due to other factors.

Soy contains a group of chemicals called isoflavones. In our bodies, these act like mild versions of the hormone oestrogen. Many human cancers, such as breast cancer, are linked to high levels of this hormone. So some scientists believe that by taking the place of our own oestrogen, soy isoflavones can reduce the risk of hormonal cancers. Others are concerned that for the same reasons, isoflavones could actually increase the risk of some cancers.

Clinical trials are needed to say for sure if soy reduces or increases the risk of cancer.

Tomatoes

Tomatoes may reduce the risk of prostate cancer but we don't know for sure.

Tomatoes contain a chemical called lycopene. This is found in all forms of tomatoes and tomato products including fresh, tinned, paste, juice and ketchup. Lycopene is a powerful antioxidant and mops up free radicals that could damage DNA.

It is unclear if lycopene could actually reduce the risk of prostate cancer. A large study of 47,000 men found that eating 2-4 weekly servings of tomatoes reduced prostate cancer risk by a quarter. But the results of other studies disagree, and there are questions still to answer. We are still unclear on what dose of lycopene would be needed to reduce cancer risk. Recently, the US FDA said that there was 'no credible evidence' that lycopene could reduce the risk of prostate cancer or other types.

Eating lots of tomatoes will help you get your recommended five portions of fruit and vegetables a day. They are also an excellent source of vitamins A, C and E.

Vitamin and mineral supplements

Vitamin supplements do not substitute for a healthy diet.

Vitamin supplements do not have the same benefits as getting naturally-occurring vitamins in your food. It is thought that in fruit and vegetables, vitamins and nutrients interact with other chemicals to produce positive effects. On their own, they could be much less beneficial. Several clinical trials have looked at the effects of vitamin supplements on cancer risk. Some of these have found that very high doses could actually increase the risk of cancer.

The best way to get your full range of vitamins and minerals is to eat a healthy, balanced diet, with a variety of fruit and vegetables. Supplements do not substitute for a healthy diet, although some people may be advised to take them at certain times in their lives. For example, doctors may advise women who are planning to have a baby to take a daily 400-microgram supplement of folic acid. And dark-skinned or elderly people may need to take vitamin D supplements since they need more sun exposure than other people to make enough vitamin D.