Portion Size & Energy Intake: A key nutritional concept we must now understand to address obesity

肥胖的增加是由能量摄入的增加引起的，其中一个关键的环境因素可能是食物的份量。在过去的三十年里，各种各样的食物的份量都有所增加。这是一个令人担忧的问题，因为实验数据显示，人们会清理自己的盘子，吃下他们端来的大部分食物。到目前为止，我们有非常令人信服的敏锐的实验室数据表明，食物的份量很可能是能量摄入的关键驱动因素；我们在一顿饭中得到的能量或食物中提供的能量的数量会影响我们消耗的能量。正因为如此，减少份量的目标可能是解决肥胖的关键方法，最近委托的公共卫生报告支持这一观点。然而，我们目前缺乏一个理论模型，能够1)解释为什么份量对能量摄入量产生如此强烈的影响，2)确定我们可以做出的份量减少的幅度，以促进可靠的长期能量摄入量的减少。这是一个主要的绊脚石，因为在我们确信利用份量有助于解决肥胖问题之前，我们需要了解为什么份量会影响能量摄入，以及如何重新制定份量。最近的研究表明，减少食物份量是非常重要的，因为如果不是这样，任何减少的能量都可能被后来的补餐所抵消。本研究的目的是开发和测试一个理论模型来解释份量对能量摄入量的影响，然后应用这一知识来测试我们如何减少份量以促进可靠和持续的能量摄入减少。我们的理论模型建立在一个既定的框架上，并基于这样一个前提，即当提供一份食物时，个体对这一部分的大小进行了简单的感知分类，要么是正常的，要么是不正常的。如果一份食物被归类为“正常”，消费者很可能会吃掉所提供的大部分食物。尽管这种知觉分类在认知上是有效的，但相对较大的份量范围似乎是正常的。我们预测，在这个“正常范围”内，食物份量的任何增加或减少都会对能量摄入产生显著影响。因此，我们提出的模型试图解释为什么分量大小会对各种食物的摄入量产生如此强烈的影响，因为消费者仍然认为他们吃了一顿正常大小的饭。这笔研究经费将对我们提出的理论进行实证检验，并检验减少份量对能量平衡的影响。在此过程中，这项工作汇集了食欲、健康心理学、视觉感知和公共卫生领域的专家，以了解食物的份量和能量摄入量。关键的是，我们的理论模型表明，可能存在一些边界条件，这些边界条件决定了减少份量何时将不再对能量摄入产生可靠的影响。通过测试这些边界条件，我们将处于一个独特的位置来检查促进能量摄入持续减少所需的份量减少的大小。在这样做的过程中，我们将产生关于我们如何为公众健康利益重新制定分量大小的重要知识。到三年计划结束时，我们将测试为什么份量影响能量摄入量的理论解释，并应用这一知识来测试是否有可能使用份量原则来促进能量摄入量的持续减少。这些新颖的见解将与食品业和公共卫生倡议直接相关，这些倡议旨在减少份量，以帮助解决普遍存在的肥胖问题。

Rises in obesity have been caused by increases in energy intake and a key environmental factor which may responsible for this is portion size. Over the last thirty years portion sizes for a wide variety of foods have increased. This is a cause for concern because experimental data shows that people 'clear their plate' and eat most of the food they are served. To date, we have very convincing acute laboratory data showing that portion size is likely to be a key driver of energy intake; the amount of energy we are served at a meal or provided in a food portion influences how much energy we consume. Because of this, targeting reductions to portion size could be a key approach to tackling obesity and recently commissioned public health reports support this view. However, we currently lack a theoretical model which is able to 1) explain why portion size exerts such a strong effect on energy intake and, 2) identify the magnitude of reductions to portion size we can make to promote reliable long-term reductions to energy intake. This is a major stumbling block because before we can be confident that exploiting portion size will help to tackle obesity, we need to understand why portion size influences energy intake and how to reformulate portion sizes. Recent research has shown that it is critical that reductions made to portion size are informed by a theoretical model, because if not, it is likely that any energy reductions made could be cancelled out by later compensatory eating. The aim of the present research is to develop and test a theoretical model to explain the effect that portion size has on energy intake, before applying this knowledge to test how we can reduce portion sizes to promote reliable and sustained reductions to energy intake. Our theoretical model builds on an established framework and is based on the premise that when presented with a food portion, individuals make a simple perceptual categorisation of the portion being either 'normal' or abnormal in size. If a portion is categorised as being 'normal' a consumer would be likely to eat the majority of the food provided. Although this kind of perceptual categorisation is cognitively efficient, a relatively wide range of portion sizes appear 'normal'. We predict that this causes any increases or decreases to portion sizes which sit inside this 'normal range' to have marked effects on energy intake. Thus, our proposed model attempts to explain why portion size can exert such a strong effect on intake for a variety of foods, with consumers still believing they have eaten a 'normal' sized meal. This research grant will empirically test our proposed theory and examine the effect of reducing portion size on energy balance. In doing so, this work brings together experts in the fields of appetite, health psychology, visual perception and public health, in order to understand portion size and energy intake. Critically, our theoretical model suggests that there are likely to be boundary conditions which determine when a decrease to portion size will cease to have a reliable effect on energy intake. By testing these boundary conditions we will be in a unique position to examine the size of portion size reductions required to promote a sustained decrease in energy intake. In doing so we will generate important knowledge about how we can go about reformulating portion sizes for public health benefit. By the end of the three year programme we will have tested a theoretical account of why portion size influences energy intake and applied this knowledge to test whether it is possible to use portion size principles to promote sustained reductions to energy intake. These novel insights will have direct relevance to the food industry and public health initiatives which aim to make reductions to portion size in order to help tackle the widespread obesity problem.