Some of you may have been aware of the recent research that has linked the eating of white bread with an increased risk of cancer. The study, published in the International Journal of Cancer, found that individuals eating the most white bread (equivalent to five slices of bread a day) were almost twice as likely to develop cancer of the kidney compared to those eating the least (equivalent to about one-and-a-half slices a daily).
Research of this nature what is known as ‘epidemiological’ in nature. This means researchers are essentially looking for associations between, say, lifestyle factors and disease. However, it’s always important to remember that an association between two things does not ‘prove’ that one thing causes the other. For example, owning a car is associated with an increased risk of heart disease. We need to be wary about, though, about then concluding that cars cause heart disease. Actually, it’s probably not owning a car that is the true risk factor that explains this association – it’s more likely to be something else that usually comes with car ownership (such as the more sedentary way of life) that is really to blame.
So, when an epidemiological study like the one linking white bread to kidney cancer comes to light, the next step is usually to at least try to explain what might explain the association. Well, one thing we know about white bread is that it offers very little in the way of nutritional value. Certain nutrients, including selenium, are believed to have anti-cancer properties. White flour is basically denuded of such nutrients – it’s not really food, more fodder. So, eating a lot of white bread may simply squeeze out of the diet more nutritious foods that might have disease-protective properties.
Another potential explanation for the link between white bread and cancer is, though, that white bread does actually cause cancer. White bread releases sugar relatively briskly into the bloodstream (it is what is known as a high ‘glycaemic index’ food). This will tend to get the body secreting a lot of the hormone insulin (the chief hormone responsible lower sugar levels in the bloodstream). There is some evidence that the biochemical changes this process induces may have cancer promoting effects within the body. The following piece dissects these processes in more depth.
The study published recently in the International Journal of Cancer is not the only research which has linked foods of high glycaemic index (GI) with increased risk of cancer. For instance, a study published last year [1] found a similar link with regard to breast cancer in post-menopausal women. Other research has linked diets of higher GI with significantly increased risk of prostate cancer [2].
There are lots of reasons why eating refined grains such as white bread as a staple food is not to be advised. The evidence already links the eating of such foods with obesity and diabetes. I suspect that evidence will eventually mount up to show that it boosts our risk of cancer too.
Observer Column – 4th December 2005
Recent times have seen breast cancer making its way up the political agenda, and awareness of this condition and the coffers of breast cancer charities have been augmented through fund-raising activities such as sponsored moonlit walks and the sale of pink ribbons and wristbands. On a recent trip to the United States I discovered that the confectioner Mars is now producing special edition packs of pink M and Ms for sale, a proportion of the profits from which are to be donated to a leading breast cancer foundation. On the surface, this looks like a sweet enough way to raise money for an important and deserving medical cause.
The selling of chocolate to help fund efforts to combat breast cancer reminded me, however, of recent research linking the eating of sweet foods with this very disease. This research, published in the Annals of Oncology, involved assessing the diets of more than 5000 women for their intake of sweet foods such as biscuits, cakes, sugar and chocolate [3]. This study found that compared to women with relatively low levels of consumption of sweet foods, those with the highest intake had a 19 per cent increased risk of breast cancer. The authors of this study concluded that they had found a direct association between breast cancer risk and the consumption of sweet fare.
Some scientists believe that the link between sugary foods and increased cancer risk has something to do with the rapid speed with which such foods tend to release their sugar into the bloodstream. The consumption of such foods, termed ‘high glycaemic index’ (GI) foods, generally stimulates the secretion of substantial quantities of the chief blood-sugar lowering hormone insulin. The consumption of high GI foods also seems to affect the activity of a related compound known as insulin-like growth factor (IGF), which is believed to have cancer-promoting properties.
The activity of IGF is to some degree modulated by other related substances known as ‘IGF binding proteins’ (IGFBPs). In a study published earlier this year in the American Journal of Clinical Nutrition, the consumption of a high GI meal, compared to slower sugar-releasing food, was found to lead to changes in the levels of two types of IGFBP [4]. It has been suggested that such changes promote the activity of IGF, and in so doing raise cancer risk. Interestingly, the consumption of high GI foods has previously been linked with an enhanced risk of not just breast cancer, but other cancers too including those of the ovary, pancreas and colon. Bearing this in mind, I wonder whether the selling of confectionery to raise money for the combating of cancer is such a good idea after all.
References:
1. Silvera SA, et al. Dietary carbohydrates and breast cancer risk: a prospective study of the roles of overall glycemic index and glycemic load. Int J Cancer. 2005 114(4):653-8
2. Augustin LS, et al. Glycemic index, glycemic load and risk of prostate cancer. Int J Cancer. 2004 10;112(3):446-50
3. 3. Tavani A, et al. Consumption of sweet foods and breast cancer risk in Italy Ann Oncol. 2006 Feb;17(2):341-5. Epub 2005 Oct 25
4. Brand-Miller JC, et al. The glycemic index of foods influences postprandial insulin-like growth factor”binding protein responses in lean young subjects. Am. J. Clinical Nutrition 2005;82: 350 – 354
