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High starch diets associated with increased risk of type 2 diabetes

Posted Aug 06 2010 12:51am

Last week one of my blogs focused on story regarding the spiralling costs of medication for diabetes. I suggested that one reason for this is that many diabetics are advised to eat a diet rich in starchy carbohydrate, yet these foods generally are very disruptive to blood sugar levels. Yes, that’s right – diabetics who by definition tend to run high blood sugar levels are often advised to eat plenty of foods that cause high blood sugar.

In that blog post I cited a study which showed that low carbohydrate eating allowed more than 95 per cent of type 2 diabetics to reduce or eliminate their medication. This, by the way, does mirror what I see in practice. Low-carb eating is not a sure-fire way of controlling blood sugar in every individual with diabetes, but one thing I know for sure is that by an large this is a highly effective strategy (and for quite obvious reasons too, I think).

Could low-carb eating have some value in the prevention of type 2 diabetes? In theory, yes. And here’s why:

As distinct from type 1 diabetes (in which the pancreas produces little or no insulin), many individuals with type 2 diabetes make lots of insulin, it’s just not doing its job properly. This situation is described as ‘insulin resistance’, and the more insulin one secretes over the course of one’s life, the more likely one is to become insulin resistant. Eating less blood sugar-disruptive carb could, therefore, lead to generally lower levels of insulin and less risk of insulin resistance.

Some type 2 diabetics are suffering from a degree of ‘beta-cell exhaustion’. It is the beta cells in the pancreas that make insulin. The harder these cells are worked during our lifetime the more likely they are to get exhausted. Now we have the potential of low levels of insulin. The risk here is that some people can end up secreting low levels of not-very-effective insulin.

Anyway, one doesn’t need a PhD to realise that eating a lower carb diet will generally lower insulin levels and make less demands on the pancreas. In short, common sense dictates that a carb-controlled diet should help prevent type 2 diabetes.

The best way to confirm or refute this concept would be to randomise people to a high- or low-carb diet, follow them up over time (preferably, several years) and see if the lower-carb dieters had lower risk of type 2 diabetes compared to the higher-carb eaters. I can’t find such a study in the scientific literature, and have a hunch such a study is unlikely ever to be done.

The next best thing is to look at populations (preferably large ones) and see if, over time, there is any relationship between carbohydrate intake and risk of type 2 diabetes. This is precisely what a group of researchers from the Netherlands did recently, and their findings were published on-line this week in the American Journal of Clinical Nutrition.

In this study, almost 38,000 adults were followed for an average of 10 years. The researchers looked at the relationship between not just carb intake and type 2 diabetes, but also the tendency of those carbs to disrupt blood sugar. Specifically, the researchers assessed the relationship between the glycaemic index (GI) and glycaemic load (GL). The glycaemic index is a measure of the speed an extent to which a standard weight of food releases glucose into the bloodstream. The glycaemic load takes into account the amount of carbohydrate eaten too, and therefore generally gives a better indication of the overall amount of blood sugar disruption that comes from food.

In some of their analyses the researchers took account of factors that might affect diabetes risk including age, sex, levels of physical activity and other dietary factors. In these analyses it was found that:

Higher carbohydrate was associated with a 20 per cent increased risk of type 2 diabetes

Higher dietary GI was associated with an 8 per cent increased risk of type 2 diabetes

Higher dietary GL was associated with a 27 per cent increased risk of type 2 diabetes

Higher sugar consumption was not associated with a statistically significant increase in risk of type 2 diabetes

Higher starch consumption was, however, associated with a 23 per cent increased risk of type 2 diabetes

The authors also quote other studies that have attempted to discern what, if any, dietary GI or GL has with diabetes risk. While not all studies show a link, six do (and therefore are consistent with the findings of this latest study). So, by my calculations that’s now seven studies we have linking high GI and/or GL with enhanced diabetes risk.

Now, I know there will be some that claim that the evidence is ‘inconclusive’ here, but that’s a matter of opinion. To my mind, science, and of course common sense, support the idea that if we’re keen on doing what we can to protect ourselves from type 2 diabetes, we need to be a bit careful with those carbs, and not swallow whole without thinking the conventional advice that tells us we can safely and happily have our fill of them.

References:

1. Sluijs I, et al. Carbohydrate quantity and quality and risk of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition–Netherlands (EPIC-NL) study. Am J Clin Nutr 4 August 2010 [epub ahead of print]

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