High glycaemic index and glycaemic load foods associated with increased risk of breast cancer

It’s a basic nutritional belief of mine that eating healthily means, at least in part, not eating too much in the way of foods that disrupt blood sugar and insulin levels. Gluts of insulin are known to have the capacity to cause fat accumulation in the body, and likely increase the risk of chronic conditions including type 2 diabetes and cardiovascular disease. Last week, my experience with a patient triggered a blog post in which I lamented the fact that this sort of core nutritional information does not seem to have been embraced by the dietetic fraternity. Read the comments that follow this post, and it is clear that some (though not all) dieticians seem none to keen on engaging in an intelligent debate about this dietary approach, and are more inclined to launch personal attacks regarding my character and motivations.

Now, while eating a low GI/GL diet may not fit particularly well with the conventional low-fat paradigm, and is certainly something that some food manufacturers would prefer you knew nothing about, there is nonetheless mounting and considerable evidence that adopting this way of eating can have very broad benefits for health.

By way of example, I’m going to focus today on a study which is published in this month’s edition of the American Journal of Clinical Nutrition. In this study, Italian researchers examined the relationship between the GI and GL of the diet and breast cancer risk in about 9000 women [1]. High GI/GL foods are believed to have the capacity to stimulate cancer growth through a variety of mechanisms, including the alteration in the levels of a substance called insulin-like growth factor 1 (IGF1) and effects on the activity of sex hormones in the body.

In this study, women with the diets of highest GI, compared to the lowest, were found to be at a 57 per cent increased risk of breast cancer. The association with Gl was even greater: those consuming the highest GL diets were at more than 2½ times the risk of breast cancer compared to women consuming the lowest GL diets.

Further analysis, however revealed that these associations were confined to premenopausal women. In these, risk of breast cancer in those consuming the highest GL diets were almost 4 times more likely to suffer from breast cancer compared to low GL diet consumers. Another finding of this study was that women of ‘healthy’ weight (as defined by a body mass index of less than 25) eating a high GL diet were found to be at increased risk of breast cancer, while heavier women were not. In women with BMIs of less than 25, a high GL diet was associated with an almost 6 times increased risk of breast cancer.

So-called epidemiological studies of this nature cannot be used as ‘proof’ that high GI and/or GL diets cause breast cancer. One reason for this, is that eating a high GI/GL diet might be associated with other thing (e.g. increased smoking, greater use of the contraceptive pill) that are, in fact, responsible for the increased risk. In this study, though, these and other so-called ‘confounding factors’ were accounted for, which strengthens the apparent relationship between GI/GL and breast cancer risk.

For more on the relationship between high GI/Gl foods and cancer risk, see my blog post of 23rd October 2006 and its accompanying article.


1. Sieri S, et al. Dietary glycemic index, glycemic load, and the risk of breast cancer in an Italian prospective cohort study Am J Clin Nutr 2007 86: 1160-1166.

2 Responses to High glycaemic index and glycaemic load foods associated with increased risk of breast cancer

  1. helen 14 October 2007 at 10:15 pm #

    Considering according to website information back in ….
    “In 1924, Warburg claimed that cancer, malignant growth, and tumor growth are caused by the fact that tumor cells mainly generate energy (as e.g. adenosine triphosphate / ATP) by non-oxidative breakdown of glucose (a process called glycolysis). This is in contrast to “healthy” cells which mainly generate energy from oxidative breakdown of pyruvate. Pyruvate is an end-product of glycolysis, and is oxidized within the mitochondria. Hence and according to Warburg, cancer should be interpreted as a mitochondrial dysfunction.

    “Cancer, above all other diseases, has countless secondary causes. Almost anything can cause cancer. But, even for cancer, there is only one prime cause. The prime cause of cancer is the replacement of the respiration of oxygen (oxidation of sugar) in normal body cells by fermentation of sugar” — Dr. Otto Warburg Lecture delivered to Nobel Laureates on June 30, 1966 at Lindau, Lake Constance, Germany.

    According to Dr. Warburg, cancer languishes with oxygen and thrives with sugar.”

    Warburg is not the only doctor or scientist to show how sugar is the main culprit in the formation & growth of cancer at the celluar level see Dr Rath’s research amongst many others. The only people that do not want this to be true are those that head up the industries responsible for manufacture & growth of sugar & sugar producing food stuffs & of course some of those involved in the billion dollar cancer industry!

  2. Carol Homer 17 October 2007 at 4:22 pm #

    Just to put another view that I heard on Radio 4’s Women’s Hour today (I expect you could ‘listen again’ if you have the facilit) that oestrogen (can never spell this) in cow’s milk is taken up by those of us that drink, use it on cereals etc and might be one factor in the formation of cancer cells. I suspect that anyone involved in the production of milk might want to refute this. I remain open-minded!!!!

    I do know that as a hyperthyroidic adult and having had asthma since 2, I feel better (cannot be measured) if I exclude milk, flour and sugar from my diet, but I do love chocolate!!!!!

    Carol Homer

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