Low GI diet outperforms high fibre one in diabetics

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Diabetes is condition characterised by higher-than-normal levels of sugar in the bloodstream. It’s a problem caused by either not enough insulin and/or insulin not doing its job. Either way, the result is generally raised levels of sugar. One effect of this is a greater tendency to combine with protein in tissues (called ‘glycation’) which can damage them and predispose to problems such as eye disease and blindness, nerve damage and kidney damage.

Because diabetes is essentially a condition where the body has difficulty moderating sugar levels in the body, it makes sense for diabetics to avoid eating much in the way of foods that tend to be disruptive for blood sugar levels. This thinking has led to at least some popularity for low glycaemic index (GI) diets among diabetics.

In a study published today, a low GI diet was tried in half a group of 210 type 2 diabetics over a 6-month period. Individuals had levels of HbA1c (also known as glycosylated haemoglobin) measuring at the start and finish of the study. HbA1c levels give a guide to the general level of blood sugar control over the preceding 3 months. Over the course of the study, HbA1c levels dropped significantly. HbA1c levels are measured as a percentage, where healthy percentages are generally less than 5 per cent. Diabetics tend to have higher levels. Overall, HbA1c levels dropped 0.5 per cent.

Another blood parameter monitored in this study was levels of high-density lipoprotein (HDL) cholesterol. This is the forming of cholesterol associated with a reduced risk of cardiovascular disease. On average, in individuals eating a low GI diet, HDL levels went up by a statistically significant amount: 1.7 mg/dL (0.04 mmol/L).

While half of the 210 people in this study were assigned to eat a low GI diet, the other half were assigned to eat a diet rich in cereal fibre. Testing such a diet makes good sense, because diabetics are often recommended to eat a diet rich in cereal (starch), with the some time proviso that should be wholegrain in form and therefore rich in fibre. The problem with this sort of diet, as I see it, is that with a diet rich in cereal fibre the diet may also be rich in cereal, and some cereal products are actually quite disruptive for blood sugar levels, particularly when eaten in quantity.

As it happens, individuals on the fibre-rich diet didn’t fair as well as those onf the low GI diet: HbA1c levels dropped by only 0.18 per cent, and HDL levels actually dropped by 0.2 mg/dL, though this was not statistically significant. What this study shows is that a low GI diet outperforms a diet rich in cereal fibre in type 2 diabetics. And it’s another example of why we need to be wary regarding the conventional dietary advice given to diabetics.


Jenkins DJA, et al. Effect of a Low”Glycemic Index or a High”Cereal Fiber Diet on Type 2 Diabetes: A Randomized Trial JAMA. 2008;300(23):2742-2753.

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