Whole grain bread is a good dietary source of complex carbohydrates, fiber, iron, vitamin E and B vitamins. White bread (made primarily from refined wheat flour) also is a source of iron and B vitamins (thiamine, niacin, riboflavin and folic acid). It contains essentially no fiber. Whole grain bread typically (but not always) has a lower glycemic index than white bread, but both have a relatively high glycemic index compared to most non-grain based foods.
The glycemic index of a food is based on the typical increase in blood sugar occurring after the food is eaten; glycemic load takes portion size into account as well. High glycemic index/glycemic load foods have been suspected of increasing cancer incidence and this possible association has been studied extensively. However, it has been found that, generally speaking, glycemic index and glycemic load are not in and of themselves significant predictors of cancer incidence. Nevertheless, high levels of bread and pasta consumption were found to be associated with higher risk of ovarian cancer among Italian women in one study. Note that a separate web page covers the effect of consuming wheat bran on risk of breast cancer.
Pronyl-lysine, a component of bread crust, has been found to suppresses carcinogen-induced colon cancer in rats. White bread consumption has been found to be associated with lower risk of upper digestive tract (oral, pharyngeal, laryngeal, and esophageal) cancers. The B vitamins found in bread have been found to be protective against cervical cancer. The folate (folic acid) in bread is assumed to be protective against cancer since deficiency of folic acid has been shown to cause DNA damage similar to the DNA damage observed in cancer cells (however, note that high serum levels of folate can stimulate cancer cell growth).
Breast cancer-related effects of eating bread
Diets high in carbohydrates tend to eventually result in chronically elevated insulin levels, which are thought to increase breast cancer risk by stimulating insulin receptors or through insulin-like growth factor I (IGF-I)-mediated cell division. Insulin-resistance, such as that which typically occurs in obesity, increases the body's insulin response to carbohydrate consumption. Women with type 2 diabetes are known to have a higher risk of breast cancer than the general population. Nevertheless, most (but not all) studies have found no significant associations between the consumption of bread (whether white or whole wheat) or the proportion of high glycemic index foods in the diet and overall risk of breast cancer. However, more relationships with breast cancer risk have been observed in studies that analyzed study participants based on their menopausal status and body mass index (BMI).
A 2009 study of Italian women found a higher risk of breast cancer among those consuming high levels of bread and pasta. Another 2009 study of 74,942 women in the Shanghai Women's Health Study found diets with high overall carbohydrate intake and high glycemic load to be associated with increased breast cancer risk in premenopausal women. A major study of Swedish women found an inverse association between consumption of high-fiber bread and breast cancer, especially ER+ breast cancer. A study of Northern Italian women found that a high-glycemic load diet may increase the risk of breast cancer, especially for premenopausal women with BMI lower than 25. Based on these studies and others that we have reviewed, a diet comprising a great deal of bread and other high glycemic foods may increase the risk of breast cancer for both premenopausal and postmenopausal women. This risk may be heightened for normal weight women compared to overweight women, especially premenopausal women with BMI lower than 25. (Note that other studies have found that being overweight is protective against breast cancer for premenopausal women, a finding that has yet to be adequately explained.) A 2011 study found a link between increased starch intake after a diagnosis of early-stage breast cancer and a greater risk of recurrence.
Bread does not appear to contain carcinogenic compounds, per se, and its contribution to breast cancer risk is likely to be subtle and limited in the short term. What is to be avoided is a diet that revolves around eating many types of white bread on a daily or regular basis, for example croissants, baguettes, toast, bagels, sandwiches, kaiser rolls, flatbread, focaccia, pita bread, crackers, dinner rolls, hamburgers and pizza.
While there was a great deal of concern a few years ago about the cancer-causing potential of acrylamides found in French bread and toasted bread, population studies found few and limited associations between the levels of acrylmides in these foods and the risks of various cancers. However, a 2012 Danish study reported that pre-diagnostic exposure to acrylamide was associated with increased mortality among breast cancer patients with ER+ breast cancer.
Below are links to recent studies concerning this food. For a more complete list of studies, please click on bread.