The insulin index is a measure of the plasma levels of insulin in response to a particular food. These values are created by comparison to the rise in plasma insulin in response to an equal quantity of standard food, which is often white bread (ascribed an insulin index of 100). The insulin load is a measure of the plasma insulin level based on the insulin index, but it takes into account the amount of food ingested. Fibre, dietary protein, high water content and small serving size can all reduce the insulin load of foods with a high insulin index because they reduce the speed of glucose absorption to the blood. The insulin index and insulin load are therefore useful biomarkers for clinical trials and epidemiological research interested in finding associations between insulin response and disease, and are generally considered more useful that glycaemic index and glycaemic load.
It has been established that frequent consumption of foods with a high insulin index, that elicit a high insulin load, are associated with the development of obesity and diabetes, potentially through the formation of insulin resistance in skeletal muscle. Insulin resistance and hyperinsulinaemia have been hypothesised to increase the risk of pancreatic cancer because high plasma levels of insulin, glucose and C-peptide are associated with an increased risk of the disease. However, research investigating the association between insulin load and insulin index has not shown that the postprandial insulin response is able to increase the risk of cancer in normal weight, healthy individuals1. But this same research did show that in individuals with a pre-existing state of insulin resistance, who were overweight and sedentary, may have an increase in the risk of developing pancreatic cancer if exposed to a diet with a high insulin load.
These results agree with previous studies that have investigated the association between glycaemic index, glycaemic load and pancreatic cancer. Meta-analysis of these studies showed a pancreatic cancer relative risks of 1.01 and 0.99 for glycaemic index and glycaemic load, respectively. Therefore it is likely that an insulinogenic diet is not implicated in the development of pancreatic cancer, despite the association with plasma C-peptide, glucose and insulin. Insulin resistance is associated with an increase in breast cancer risk, and it is likely that pre-existing insulin resistance increases risk of pancreatic cancer in the presence of a high insulin load diet. This is supported by data showing a positive association between pancreatic cancer and fasting insulin levels. In addition, drugs such as metformin that are able to reduce insulin resistance without affecting insulin secretion, can inhibit the development of pancreatic cancer in animal models.
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