Refined carbohydrates cause Western disease because they are stripped of their fibre and micronutrients during processing. In particular, fructose is particularly damaging when removed from the whole fruit and consumed as fruit juice or its crystalline form in processed foods. Refined carbohydrate diets are therefore diets with low fibre to starch ratios and it is this that is the driver for insulin resistance, the probable cause of metabolic syndrome. The benefits of fibre in the diet have been demonstrated in numerous clinical trials, data which is supported by inverse associations between Western diseases and fibre intake. The benefits of fibre are likely multifactoral, but centre on the ability of the fibre to lower the glycaemic effects of food and thus control the rate of delivery of sugars to the liver for processing. This is an important concept to understand, because high rates of carbohydrate delivery to the liver results in hepatic overload and this increases flux through the de novo lipogenesis pathway. It is the resulting lipids that are deposited in tissues that are the probably cause of insulin resistance.
Gum fibres from legumes have been reported to be particularly beneficial at reducing the glycaemic effect of food. This likely relates to their ability to dramatically increase the viscosity of the chyme in the gut, thereby slowing its digestive progress. Comparisons of gums have been made in vitro1, with viscosities being reported to be inversely related to the concentration of the gum and the shear rate (the rate of deformation of the fluid in a tube), although the relevance of these measurements to the human gut is questionable. Results from this study showed that guar gum had a higher viscosity in solution when compared to locust bean gum, and was over twice as viscous as xanthan gum. Combining gums significantly increased their viscosities, with a xanthan / locust bean gum mixture being over 4 times as viscous as guar gum, the best performing isolated gum. Acidification (to simulate entry to the stomach) and re-neutralisation (to simulate entry to the small intestine) caused changes in the viscosity of the gums, however, there was no clear pattern in these changes,
When the gums were tested in human subjects, only the xanthan / locust bean gum combination significantly slowed gastric emptying compared to a control. Glucose tolerance was significantly improved by addition of 2.5 grams of xanthan, xanthan / locust bean, xanthan / Meyprodin or guar gum when compared to a glucose drink, with lower blood glucose curves being altered differently in each gum. Guar and the xanthan / locust bean gum were considered equally effective at lowering the blood glucose levels, but locust bean gum alone had no effect. All gums reduced the area under the glucose profile, but only xanthan gum showed statistical significance. All the gums tested in the human volunteers reduced the insulin responses to glucose but guar and the xanthan / locust bean gums had the greatest effects. Therefore the in vitro prediction of the glycaemic effects are not straight forward, because although the xanthan / locust bean gum had a significantly higher viscosity in vitro, it was not significantly better at reducing plasma insulin or glucose compared to other gums.
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