Insulin again implicated in breast cancer

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We have, for a long time, been wary that certain dietary habits are linked to and perhaps predispose people to cancer. The usual whipping boy here is ‘red meat’ – which is often said to be a potential trigger factor in, say, colon cancer. This belief will tend to add the comfort and security some people will get from eschewing red meat and other ‘fatty foods’ in favour of a diet rich in carbohydrate, including ‘complex carbohydrates’ like bread, potatoes, rice, pasta and breakfast cereals.

However, in recent years there has been some talk about the potential role supposedly healthy starch carbs have in cancer. These foods, particularly when eaten in quantity, can lead to high and sustained levels of glucose in the bloodstream, which in turn can lead to surges in the secretion of the hormone insulin. Insulin lowers blood sugar (which is good) by facilitating its transfer out of the bloodstream into the body’s cells. But it does other thing too, including stimulate the proliferation of cells, which enhances the risk of uncontrolled, rogue cell division that is the basis for cancer.

Previous research, has linked the consumption of the most blood sugar disruptive carbohydrates (high glycaemic index carbohydrates) with an increased risk of breast cancer.

Also, other worked has found that women suffering from ‘metabolic syndrome’ are at heightened risk of breast cancer after the menopause [1]. The potential relevance of this is that one of the common features of metabolic syndrome is ‘insulin resistance’ – a state where the body does not respond normally to insulin, which itself is thought to be the result of chronically elevated levels of insulin.

The same group of researchers responsible for the work on breast cancer and metabolic syndrome has recently published a study which has focused in on the potential link between insulin resistance and post-menopausal breast cancer risk [2]. What they found was that insulin resistance was more common in women with breast cancer than in those without (as expected).

Insulin resistance was assessed in these women using a standard test known as ‘HOMA-IR’ (homeostatic model assessment – insulin resistance) which calculates insulin resistance based on fasting levels of both glucose and insulin. One of the interesting things about this study is that it found that in the majority of women with insulin resistance, blood sugar levels were normal. Essentially, what this means is that the evidence for insulin resistance came from elevated levels of insulin (in the absence of elevated levels of blood glucose).

This does not mean, however, that the blood sugar levels in these women are truly normal. There are people, for example, who have normal fasting levels of glucose who find their blood sugar levels can rise very high when they consume carbohydrate in even quite-limited amounts.

The authors of the study suggest that assessment for insulin resistance might prove a useful tool in assessing breast cancer risk. In the meantime, women wishing to reduce their risk of metabolic syndrome and insulin resistance may do well to be wary about the blood sugar- and insulin-disruptive effects of starchy foods which some would have us believe are healthy and essential. Essential they are not, and increasing evidence shows them not to be particularly healthy, either.


1. Capasso I, et al. Metabolic syndrome affects breast cancer risk in postmenopausal women: National Cancer Institute of Naples experience. Cancer Biology & Therapy 2010;10(12):1240 DOI:10.4161/cbt.10.12.13473

2. Capasso I, et al. Homeostasis model assessment to detect insulin resistance and identify patients at high risk of breast cancer development: national cancer institute of Naples experience. Journal of Experimental & Clinical Cancer Research 2013;32(1):14 DOI:10.1186/1756-9966-32-14

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