By Thomas S. May
BUDAPEST, HUNGARY -- April 26, 2007 -- A study presented here at the 15th European Congress on Obesity (ECO) may explain why a meal with a low glycaemic index (GI) typically results in greater feeling of fullness than a similar meal with a high GI.
"Low GI foods have been linked to decreased appetite," said lead author Rebecca Reynolds, PhD candidate, School of Molecular and Microbial Biosciences, University of Sydney, New South Wales, Australia. "They also have been shown by several studies to help with weight loss," she went on to say.
The senior researcher for this study was Jennie Brand-Miller, PhD, professor, molecular and microbial biosciences, faculty of medicine, University of Sydney, Sydney, Australia.
The glycaemic index is a scale that ranks carbohydrate-rich foods by how much they raise blood glucose levels.
Therefore, Reynolds and colleagues sought to quantitatively determine the effect of glycaemic index on satiety by measuring gut peptides. They hypothesised that low GI meals would increase production of the satiety peptide cholecystokinin (CCK) and decrease the production of grehlin, a hormone associated with hunger.
To test their hypothesis, the investigators had 12 young, healthy males with a mean age of 23.2 years consume a high and low GI diet in random order at least one week apart. Each diet consisted of four meals, and they were matched for energy and all macronutrients (i.e., fat, carbohydrates, and protein). The only difference between the two diets was in carbohydrate quality (i.e., high or low GI).
Subjects were observed for 10 hours each day, during which time blood samples were drawn every 30 or 60 minutes, and the samples were analysed for CCK and grehlin, as well as glucose and insulin.
The researchers found that the high GI diet resulted in significantly higher day glucose and insulin AUCs (high GI glucose 356 mmol.10h/L vs low GI glucose 221 mmol.10h/L, P =.027, and high GI insulin 63,629 pmol.10h/L vs low GI insulin 25,151 pmol.10h/L, P =.001, respectively).
Cholecystokinin increased postprandially, as expected, with a larger day AUC on the low GI diet (high GI 284 pmol.10h/L vs low GI 472 mmol.10h/L), but the differences did not reach statistical significance (P =.224). However, there was a statistically significant difference in cholecystokinin secretion 3 hours after consuming the high compared with low GI meals (P =.0498).
"These results suggest that an increased blood concentration of the satiety peptide cholecystokinin may contribute to greater feelings of fullness after low GI meals," Reynolds said. "Hence our data may provide quantitative evidence for the bulk of research supporting the use of low GI diets for weight loss in obesity," she added.
[Presentation title: Effect of the Glycemic Index of Carbohydrates on Day-Long (10 H) Profiles of Gut Hormones. Abstract HT2.PO]
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