PureInsight | November 12, 2006
Recently, research has come to light that links eating 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 daily).
Research of this nature is epidemiological. This means researchers are
essentially looking for associations between lifestyle factors and
disease. However, it's always important to remember that an association
between two things does not prove that one causes
the other. For example, owning a car is associated with an increased
risk of heart disease. We need to be wary about concluding that cars
cause heart disease. 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.
The next step is to try to explain what might cause the association.
Well, one thing we know about white bread is that it offers very little
nutritional value - it's not really food, merely fodder.
Eating a lot of white bread may simply squeeze out of the diet more
nutritious foods that might have cancer-protective properties.
Another potential explanation for the link between white bread and cancer is that white bread does actually cause
cancer. White bread is known as a high glycemic index (GI) food because
it releases sugar relatively briskly into the bloodstream. This will
cause the body to secrete a lot of insulin, the chief hormone
responsible for lowering blood sugar levels. There is some evidence
that the biochemical changes during the process may have
cancer-promoting effects.
High GI foods not only stimulate the secretion of just insulin but can
also raise levels of a related compound known as insulin-like growth
factor (IGF). This substance is believed to have the capacity to
initiate cancerous change in the cells. Also, the activity of IGF is to
some degree modulated by other related substances known as IGF binding
proteins (IGFBPs). In a study published 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. It has been suggested that such changes promote
the activity of IGF, and in so doing raise cancer risk.
Support for a link between the eating of high GI foods and cancer has come from several studies.
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 show that it boosts our risk of cancer too. Other
relatively high GI foods to avoid include wholegrain bread (its GI is
actually as high as white bread), potatoes, and white rice. Slower
sugar-releasing foods to base the diet on include meat, fish, green
vegetables, beans, lentils, and nuts.
References:
1. Brand-Miller, J.C., et al. The glycemic index of
foods influences postprandial insulin-like growth factor-binding
protein responses in lean young subjects. American Journal of Clinical
Nutrition 2005; 82: 350-354
2. Tavani, A., et al. Consumption of sweet foods and
breast cancer risk in Italy Annals of Oncology. 2006 Feb.; 17(2): 341-5
3. Silvera, S.A., et al. Dietary carbohydrates and
breast cancer risk: a prospective study of the roles of overall
glycemic index and glycemic load. International Journal of Cancer. 2005
114(4): 653-8
4. Augustin, L.S., et al. Glycemic index, glycemic
load, and risk of prostate cancer. International Journal of Cancer.
2004 10; 112(3): 446-50
Dr John Briffa is a London-based
physician, author, and health writer with a special interest in
nutrition and natural medicine. Practical advice about health and
well-being can be found at www.drbriffa.com.
