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

已知口腔加工行为会影响预期饱腹感、能量摄入和餐后饱腹感（1-3）。在健康的年轻人中，已经确定吃得慢会导致食物摄入量减少，相反，吃得快会导致摄入量增加(3)。对于老年人，缓慢进食可能不利于满足足够的卡路里和蛋白质需求，但对于确保舒适和安全的吞咽是必要的（4,5）。众所周知，咀嚼会影响食物的颗粒大小，颗粒越小，食物从胃中排空的速度就越快，也就更容易消化和吸收营养。唾液流量大的人需要更少的咀嚼周期和更短的口腔停留时间(7)。对于许多老年人来说，牙列问题和肌肉力量下降以及唾液流动减少会阻碍食物的摄入，需要他们咀嚼更长的时间以获得适合吞咽的丸状成分。这可能导致的后果是进食速度变慢，食物摄入量减少。某些食物已被证明能刺激唾液分泌（10），如果在饭前食用，可以使进食更容易。每个人的口腔加工过程有相当大的差异（1,6），然而，迄今为止的大多数研究都规定了一个固定的咀嚼制度，以确定咀嚼对食物摄入的影响。人们对自然咀嚼模式对食物摄入的影响以及通过食物途径操纵口腔加工的可能性知之甚少。我们假设，控制食物以促进唾液流动和帮助咀嚼将增加老年人的进食率和食物摄入量。该项目旨在：(1)评估食物的口腔加工对老年人食物摄入的影响程度(2)探索食物形式和食物呈现的操纵对口腔加工和食物摄入的影响。研究1将评估牙列、进食速度和口腔加工对老年人主观饱腹感的影响（年龄在60 - 70岁）。测量食物的大小，吞咽，食物在口中的时间，进食速度，每一口咀嚼和总活跃进食时间将包括在内。参与者将被要求在测试餐前和测试餐后每隔15分钟评估一次他们的饱腹感。使用13c -醋酸钠呼气试验评估胃排空。血糖和血浆胰岛素的测量将取自手指刺血样本。评估口腔容积、受刺激和未受刺激的唾液流量。标准的一口食物将被咀嚼到吞咽，然后被吐痰，这将被用来确定唾液被食物吸收以及唾液淀粉酶的产生。测量天然牙齿的数量/假牙的存在（11）以及测量咀嚼能力（12）。研究2将评估食物形态的差异以及对口腔加工和食物摄入的影响。在两天的测试中，将评估两种不同形式（固体和泥状）的单一食物，以确定咀嚼对老年人饱腹感和食物摄入量的影响。将使用与研究1类似的方法，并在初始试验餐后4小时提供自由餐，以评估对饱腹感的影响。研究3将评估添加有可能刺激唾液分泌的食物。这可能会使老年人更容易进食，并减少在口中确保食物足够柔软以吞咽所需的时间，从而提高进食率。

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.