Back in October, I wrote about some recently-published research which linked the eating of a high carbohydrate (actually, high glycaemic index and load diets) with an increased risk of breast cancer.
One way that fast sugar-releasing foods may promote cancerous growth is through the activity of a compound known as insulin-like growth factor (IGF), which is believed to have cancer-causing potential. The activity of IGF is modulated by other related substances known as ‘IGF binding proteins’ (IGFBPs). In one study, 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 [1]. It has been suggested that such changes promote the activity of IGF, and in so doing raise cancer risk.
Eating a high GI/GL diet will also, generally speaking, lead to an increase in insulin levels in the body. As insulin levels rise, so generally does the level of a substance called C-reactive protein (CRP) in the body. This substance has been linked with an increased risk of cardiovascular disease [2,3].
This week, though, the results of a study were presented which has linked higher CRP levels with worse outcomes for women with breast cancer. The study in question, was presented at the American Association for Cancer Research’s Sixth International Conference on Frontiers in Cancer Prevention in Philadelphia, USA, and I do not access to the actual study. However, it has been reported that it found that women with the highest C-peptide levels at the time they are diagnosed with breast cancer had almost twice the risk of death compared to women with lower C-peptide levels.
Perhaps because of the link between insulin and CRP, the results of this study have been reported by Reuters as: Women with breast cancer and elevated insulin levels face a significantly higher risk of death than their counterparts with lower insulin levels, research suggests.�
But what really caught my eye in the Reuters report on this study was a comment made by the study’s lead author, Professor Melinda Irwin, from Yale University’s School of Public Health, Connecticut, USA. It is claimed that she has urged breast cancer survivors to talk to their doctor about how to lower their insulin levels. Nothing too contentious here, I reckon. But she then, apparently, followed this up by saying “Breast cancer patients should take proven steps to lower their blood insulin levels, including exercise and eating a diet rich in fruits and vegetables and low in fat.” [emphasis mine]
My advice for anyone wanting to moderate insulin levels would be to watch their consumption of, not fat, but carbohydrate. After all, it’s carbohydrate that is the primary driver of insulin secretion in the body (not fat). There is even some evidence to support this commonsense approach to insulin moderation. In a study in which individuals were randomised to eat one of three diets of varying composition, those eating the diet with the lowest carb content (and actually the most fat) saw the greatest reduction in fasting insulin levels [4].
Professor Irwin’s apparent view on how best to control insulin levels may possibly be the result of some misquoting or, more likely, selective quoting. However, it might also just have been borne out of a kind of ‘nutritional correctness’ that seems to engulf this field quite commonly: ‘We’re talking about diet and health so we’d better mention fat’.
But forget about this for a moment, because more important that the effect of foods on insulin levels but the apparent effects of food on health. There is some evidence that fat intake (not even saturated fat) has no link with breast cancer risk [5]. On the other hand, as I reported in October, eating a high GI/GL diet is associated with an increased risk of breast cancer [6].
References:
1. 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
2. Ridker PM, et al. C-reactive protein and risk of cardiovascular disease: Evidence and clinical application [review]. Current Atherosclerosis Rep 2003; 5:341 -349
3. Ridker PM. High-sensitivity C-reactive protein: Potential adjunct for global risk assessment in the primary prevention of cardiovascular disease. Circulation 2001;103:1813 -1818
4. Noakes M, et al. Comparison of isocaloric very low carbohydrate/high saturated fat and high carbohydrate/low saturated fat diets on body composition and cardiovascular risk. Nutr Metab 2006;3;7.
5. Kim EHJ, et al. Dietary fat and risk of postmenopausal breast cancer in a 20-year follow-up. American Journal of Epidemiology. 2006;164:990-997
6. 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
Dr Briffa, As you can see I agree with practically all your ideas. However I must ague with your idea that fat intake has no relevance for breat cancer. I will read the evidence, but I am on a bit of a campaign to warn people about the dangers of processed veg oil (except olive) as this enters the cell membrane and affects how it works. Hormonal messages must be affecte by this.
I would like to know more because I think hydrogenated fats and processed veg oils are cancer causing.
Hilda and Sue
Let me be clear: the evidence suggests that overall fat intake has little bearing on breast cancer risk. However, it is certainly my belief that for the best health (including for cancer and other chronic disease risk reduction) there are certain fats that should be avoided, namely omega-6 fats (in excess), partially hydrogenated and industrially-produced ‘trans’ fats.
I should perhaps have been more specific about this in the piece.
Totally agree.