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Why low GI makes you feel full

Eating a low GI (glycemic index) meal will keep you feeling fuller for longer, King’s scientists have discovered in what could be the key to how the GI diet works.

Researchers from the Department of Nutrition and Dietetics in King’s College London have found that low GI (glycemic index) meals increase gut hormone production which leads to the suppression of appetite and the feeling of fullness. This is the first study to provide clues as to how a low GI meal produces satiety.

GI is a ranking assigned to carbohydrates according to their effect on the body’s blood sugar levels. A low GI meal takes longer to digest and releases sugar into the bloodstream more slowly than a high GI meal. A low GI diet is known to cause reduced appetite but the mechanisms behind this have so far remained unknown. To address this Dr Tony Leeds, Senior Lecturer in Nutrition and Dietetics, and Reza Norouzy at King’s College London looked at the effects of a single low versus high GI meal on gut hormone levels in 12 healthy volunteers.

Each participant ate an identical medium GI meal for dinner, fasted overnight, and was given either a low (46) or high (66) GI meal for breakfast. Blood samples were then taken every 30 minutes for 150 minutes, and levels of the gut hormone GLP-1 and insulin measured. GLP-1 is a hormone produced by the gut that has been shown to cause a feeling of fullness and suppression of appetite.

Volunteers who ate a low GI breakfast had 20 per cent higher blood plasma levels of GLP-1 and 38 per cent lower levels of insulin compared to those who had consumed a high GI breakfast. These results show for the first time that eating a low GI meal increases GLP-1 production and suggest a physiological mechanism as to why a low GI meal makes you feel fuller than a high GI meal.

Professor Peter Emery, Head of Department of Nutrition and Dietetics, and one of the paper’s author’s comments: “The findings of this study are an important first step in understanding how low GI foods can help to address issues of weight control and what part they should play in a balanced diet.”

Source: King’s College London Press Release 18 Mar 2009

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