Traditionally, obesity has been thought of as a simple energy imbalance, whereby calorie intake becomes too great when compared to the amount of energy expended on metabolic processes and physical activity. However, within the last decade, a picture is emerging that suggests that obesity is far more complex than previously thought, and its aetiology involves many factors not previously considered important. In particular, feeding habits such as television watching, video game playing and social eating are showing that factors such as advertising, distraction and peer involvement have significant effects on the development of obesity. In addition, factors that can affect gut hormone release can also have effects on subsequent feeding behaviour. Chewing is one such behaviour that has been investigated by researchers and found to be associated with subsequent energy intake and the level of obesity seen in subjects.
Researchers1 investigating the effects of chewing fed a group of Chinese subjects their usual breakfast that consisted of 68% carbohydrate, 21% fat and 11% protein in an ad libitum manner. The weight of food was then measured and the chewing activity was recorded with a digital camera. In a follow up study, subjects were fed a standard meal containing 60% carbohydrate, 22% fat and 18% protein in the evening, and then the following morning were requested to eat 10g portions of food with either 40 or 15 chews per portion in an ad libitum manner. The subjects then had their satiety feeling rated and the amount of food eaten recorded. The results showed that obese and non-obese subjects had similar bite sizes (≈10g), but the number of chews per gram of food was significantly less for obese subjects. The consequence of this was that the obese individuals had a significantly higher ingestion rate when compared to non-obese individuals.
Using a greater number of chews and reducing consumption rate caused the subjects to ingest 11.9% less energy. However, there was no significant effect on ratings of hunger or insulin concentrations between treatments. Plasma ghrelin was significantly lower, and plasma glucagon-like peptide-1 (GLP-1) and cholecystokinin significantly higher, after 40 chews compared with 15 chews. This suggests that increased chewing was associated with a hormonal profile amongst the gut hormones that favoured a reduced energy intake. The cephalic response to food ingestion is known to be a powerful modulator of hormonal response to food ingestion, and it is likely that increased chewing, through olfactory and taste stimulation, is able to enhance the cephalic response to food. For example, chewing gum for 15 minutes is effective at reducing appetite. Other studies have found that reduced eating speed is able to increase levels of the satiety hormones GLP-1 and peptide YY.
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