The glycaemic index (GI) is a measure of the rise in blood glucose (area under the curve) caused by a particular carbohydrate food, compared to the standard food, white bread (and expressed as a ratio). High GI foods are increasingly coming under scrutiny because of their association with blood sugar and blood lipid disorders. The GI of foods can be lowered by the combination of the food with protein, fibre or fat because these foods can slow the digestion and absorption of carbohydrate. Excluding oats, muesli and whole wheat variants, ready-to-eat breakfast cereal is almost exclusively high GI refined carbohydrates, which has had most of the fibre and micronutrients removed during processing. These types of high GI breakfast foods can cause increased hunger when compared to high fibre breakfast foods, and this may be related to their effects on blood sugar.
The processing of breakfast cereals can have a strong influence on the GI of the final product. Adding a prefermentation step using a sourdough preparation and decreasing steam cooking time may be effective at lowering the GI. Normally breakfast cereals would be prepared by heating, which results in a gelatinised starch, and this causes chemical changes within the starch (it swells and take in water) that increases its availability to amylase and increases digestion speed. Reducing cooking temperature and duration decreases the geletinisation and decreases the GI. Using a prefermentation step by incorporating natural lactobacilli, results in a sourdough preparation with high concentrations of lactic and acetic acids that slow digestion. Prefermentation also increases mineral absorption via degradation of phytates through activation of phytases, which function better in the acid environment caused by lactic and acetic acids. Removing some of the added sucrose can also be beneficial.
Childhood obesity levels are rising and high intakes of refined high GI foods are increasingly being associated with the insulin resistance that may lead to weight gain. Researchers are therefore interested in the effects that lowering GI has on hunger, blood sugar and insulin levels. Researcher1 have investigated the effects of the modified processing on the GI of breakfast cereals and the subsequent plasma insulin, glucose and ghrelin levels, following consumption. Standard wheat flakes, modified wheat flakes or white bread (control) where fed to 11 healthy male volunteer. Although the GI of the modified wheat flakes was 12% lower than the standard wheat flakes, this did not reach statistical significance. However, insulin was significantly lower at 90 minutes following consumption of the modified wheat. Hunger and plasma ghrelin were also lower in the modified wheat group, but this did not reach statistical significance.
These results suggest that the processing of breakfast cereals can have a measurable effect on human physiology following consumption. Comparison of the starch granules in the modified wheat cereal showed incomplete geletinisation, which suggests that the slower cooking time and sough dough fermentation step had been effective at altering the chemical composition of the wheat. This may have contributed to the reduction in hunger seen in the modified wheat group, which was correlated with plasma ghrelin levels. The highly processed, highly refined and sucrose rich composition of most breakfast cereals has been criticised by nutritionists because it may contribute substantially to the development of insulin resistance, metabolic syndrome and obesity when consumed as part of a Western diet. Many studies have shown the positive benefits of switching to a diet high in unrefined cereals such as oats, which contain high levels of soluble fibre and micronutrients.
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