Mastication effects on glycaemia: practical implications for diet advocacy

Background and objectives: The glycemic index (GI) is a well-established dietary tool that enables people to make healthier food choices. However, glycemic variability is a persistent observation that challenges the accuracy and use of the GI. We were interested in seeing if mastication contributed to these variations. The objective of the current study was to determine the role of mastication on glycemic response (GR) and GI. Rice was used as the test food as it is the most common staple eaten in the world and has been implicated in the diabetes epidemic.

Methods: The study adopted a randomized, controlled, cross-over, non-blind design and used 15 healthy subjects (8 males and 7 females, mean (±SD) age 26±6) who returned on five separate days for three glucose and two test rice sessions. At the rice sessions, subjects chewed each mouthful 15 and 30 times. Mastication frequency was measured with real-time electromyograms recorded using bipolar surface electrodes attached to the masseter muscles. Subjective feelings of satiety were measured with visual analogue scales.

Results: Rice chewed to a lesser extent produced a total GR (155 mmol.min/L), peak GR (2.4 mmol/L) and GI (68) significantly lower than when chewed for longer (184 mmol.min/L, 2.8 mmol/L and 88 respectively). There was no effect of mastication on satiety.

Conclusions: The study shows that mastication influences GI and contributes to variations. This is the first record to show that the GI can be affected by an intrinsic human factor although it is by definition a food property independent of such variables. It also shows that rice GR can be reduced by a simple alteration in mastication. This has significant public health implications especially in rice eating societies where it contributes a large glycemic load and increases disease risk.