Researchers at the Department of Nutrition and Dietetics at King’s College London found that low GI meals increased the levels of GLP-1 gut hormone production in the bloodstream, leading to the suppression of appetite and the feeling of fullness.
Presenting their research earlier this month at the annual society for endocrinology BES meeting in the UK, the scientists claim their study is the first to provide clues as to how a low GI meal produces satiety.
"Our results suggest that low GI meals lead to a feeling of fullness because of increased levels of GLP-1 in the bloodstream. This is an exciting result which provides further clues about how our appetite is regulated, and offers an insight into how a low GI diet produces satiety," said co-author of the study Dr. Reza Norouzy.
The GI measures how quickly certain foods release carbohydrates into the body, which then raise consumers' blood glucose levels. High GI foods cause blood sugar levels to rise more rapidly whereas a low GI rating, that takes longer to digest and release sugar into the bloodstream, provides consumers with the satiety, 'full' sensation.
Set against the backdrop of soaring obesity rates in Europe and beyond, foods that tackle weight management are enjoying particularly strong growth with a plethora of new product formulations focused on the glycemic index (GI) and satiety. Oats, for example, with a low GI rating and high satiety, are increasingly popular among snack producers as a nutritious ingredient.
According to market researchers Mintel, value sales of oats increased by 26 per cent between 2003 and 2005 and sales grew by 81 per cent from 2000 to 2005. Meanwhile, over the same five year period, volume sales also increased by a healthy 43 per cent with Britons consuming 50,000 tonnes of oat-based products in 2005.
The King's College study
While a low GI diet is known to cause reduced appetite, mechanisms, say the King's College London scientists, behind this have so far remained unknown.
Aiming to shed light on this area, Professor Peter Emery, head of department of nutrition and dietetics, Dr Tony Leeds, senior lecturer in nutrition and dietetics, and Dr.Reza Norouzy at King’s College London looked at the effects of a single low versus high GI meal on gut hormone levels in twelve healthy volunteers.
"We already know that the hormone glucagon-like peptide 1 (GLP-1) and a low GI meal independently lead to suppression of appetite. This study builds on these findings by providing a physiological mechanism to explain how a low GI meal makes you feel fuller than a high GI meal. GLP-1 is one of the most potent hormones for suppressing appetite," added Dr. Reza Norouzy.
Blood samples
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, say the researchers, 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 commented: "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."
The researchers said at the meeting that their small study was 'preliminary', adding they now need "to expand these findings and look at the effects of low versus high GI meals in a larger cohort of people."