The digestibility of carbohydrates, and their effects on blood glucose levels, may not affect our feelings of fullness as previously thought, according to a new study by Unilever scientists.
The study, published in the European Journal of Clinical Nutrition, and supported by Unilever suggests that glycemic responses to carbohydrates of different digestibility “have minimal effects of appetite”, reporting that when products which only varied in carbohydrate digestibility were tested for their effects on appetite, very little suppressive effect was found for carbohydrates that are digested more slowly.
“Our results in a study population of mostly women suggest that slowly (relative to rapidly) digestible carbohydrates will not have meaningful effects on acute appetite control when applied in food products at the levels tested in this study,” said the researchers, led by Dr Harry Peters of Unilever Research and Development, The Netherlands.
“Differences in glycemic responses were unrelated to appetite scores following consumption of test products controlled in composition and differing only in carbohydrate digestibility rate and extent … These results cast further doubt on the notion that slowly digested carbohydrates may influence appetite through their effects on glycemic responses,” they said.
Dr Peters and his co-workers said that ‘slowly digestible’ (low GI) carbohydrates have been claimed to reduce appetite through their effects on post meal (postprandial) glucose and insulin levels – known as the glycemic response.
However they noted that previous research has shown inconsistent results. They said that other studies have observed that postprandial glycemia and appetite are not related, or that blood insulin but not glucose is associated with increased short-term appetite reduction.
Such inconsistencies between study results may be due to factors other than glycemic effects, for example subtle differences in products’ nutritional or physical properties.
“One of the criticisms of previous studies testing the effect of low glycemic index products or ‘slow carbs’ on appetite is that most studies compared products differing in ways other than just the carbohydrate composition, and thus included confounding variables affecting the interpretations regarding blood glucose and/or appetite,” said Peters and colleagues.
“One way to test this is to compare test foods differing only in the digestibility of carbohydrates, but with identical chemical makeup and physical properties, and evaluate effects on the postprandial glucose, insulin and appetite responses,” they explained.
A comparison of rapidly digestible maltodextrin to differing chain lengths of the glucose-polymer pullulan would provide a test of rapidly- to slowly- to non-digestible carbohydrates, differing only in digestibility, said the researchers.
Thirty five volunteers received drinks containing 15 grams of a test carbohydrate polymer (rapidly digestible maltodextrin, slowly but completely digestible medium-chain pullulan, and indigestible long-chain pullulan), in a randomized double-blind trial.
The Unilever researchers measured carbohydrate digestibility, in addition to volunteers’ appetite scores, glucose and insulin levels.
Despite different effects on plasma glucose levels following consumption of drinks containing the maltodextrin and medium chain pullulan, appetite responses were found to be similar.
However, the authors noted that although largely indigestible polymer (long chain pullulan) led to minimal changes in blood glucose, it did produce a significant reduction in appetite scores.
Peters and colleagues said that all of the observed differences in glycemic response and appetite were apparent in a period up to 150 minutes, thus “suggesting that it was not (or only partially) [due to] a ‘slow-carb’ effect.”
“We expected that a ‘slow carb’ such as the medium chain pullulan might have reduced appetite more than the long chain pullulan, because the energy provided by the latter in the post-meal period should be small[er],” explained the researchers.
“The effect of the long chain pullulan on appetite is therefore intriguing but unexplained, and further research could be focused on this observation,” they said.
Source: European Journal of Clinical Nutrition
Volume 65, Issue 1, Pages 47-54, doi: 10.1038/ejcn.2010.189
“Effect of carbohydrate digestibility on appetite and its relationship to postprandial blood glucose and insulin levels”
Authors: H.P.F. Peters, P. Ravestein, H.T.W.M. van der Hijden, H.M. Boers, D.J. Mela