Eating rate, oral processing, gastric emptying and appetite in older adults: Investigations of food intake and food form

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BackgroundOral processing behaviours are known to impact on expected fullness, energy intake and post-meal satiety (1-3). In healthy young adults, it is established that slower eating results in a lower food intake and conversely eating quickly results in higher intakes (3). For older adults, slower eating may be detrimental to meeting adequate calorie and protein needs but necessary to ensure comfortable and safe swallowing (4,5). Mastication is known to impact on the particle size of the food (7), the smaller the particle size, the faster it will be to emptying from the stomach (8), making it also easier to digest and absorb the nutrients. People with greater salivary flow rates have been shown to require fewer chewing cycles and less time in the mouth (7). Dentition problems and reduced muscle strength, alongside reduced salivary flow, can hinder food intake for many older people (9) requiring them to chew for a longer period of time in order to achieve a bolus composition suitable for swallowing. The likely consequences of this, are slower eating rates and reduced food intake. Certain foods have been shown to stimulate salivary production (10) and could make eating easier if consumed prior to a meal. There is considerable variation in the oral processing of individuals (1,6), however the majority of research to date has prescribed a fixed chewing regime to ascertain the impact of chewing on food intake. Considerably less is known about the impact of natural chewing patterns on food intake and the potential to manipulate oral processing through food approaches. We hypothesise that manipulating foods to enhance saliva flow and aid mastication will increase eating rate and food intake in older adults.The project aims to:(1) Assess the extent of oral processing of food on food intake in older adults (2) Explore the impact of manipulation of food form and food presentation on oral processing and food intake.Study 1 will evaluate the effect of dentition, eating rate and oral processing on subjective satiety in older adults (aged >70 years of age). Measurement of bitesize, swallowing, time of food in the mouth, eating rate, chews per bite and total active eating time will be included. Participants will be asked to rate their satiety prior to, and at 15-minute intervals after, a test meal. Gastric emptying will be assessed using the 13C-sodium acetate breath test. Measurements of blood glucose and plasma insulin will be taken from fingerprick blood samples. Oral volume capacity, stimulated and unstimulated salivary flow rates will be assessed. A standardised mouthful of food will be chewed to the point of swallowing and then expectorated, this will be used to ascertain saliva uptake into food as well as salivary amylase production. Measurement of numbers of natural teeth / presence of dentures will be undertaken (11) as well as a measure of masticatory ability (12).Study 2 will evaluate difference in food form and the impact on oral processing and food intake. Across two test days a single food presented in two different forms (solid and puree) will be assessed to ascertain the impact of mastication on satiety and food intake in older adults. Similar methods to Study 1 will be used, as well as an ad libitum meal provided 4 hours after the initial test meal to assess the impact on satiety.Study 3 will evaluate the addition of foods that have the potential to stimulate saliva production. This may make eating easier for older adults and decrease the time required in the mouth to ensure sufficient softness of food for swallowing, hence increasing eating rate.