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Satiation, satiety and their effects on eating behaviour

2009; Wiley; Volume: 34; Issue: 4 Linguagem: Inglês

10.1111/j.1467-3010.2009.01777.x

1471-9827

H. Gibson‐Moore,

Eating Disorders and Behaviors

This one-day conference was held in association with the publication of a new British Nutrition Foundation (BNF) Briefing Paper entitled Satiation, satiety and their effects on eating behaviour, published in the June 2009 issue of Nutrition Bulletin (Benelam 2009). Satiation and satiety are internal mechanisms in the body involved in the regulation of food intake and, in the context of the current obesity epidemic, it is important to understand how energy intake is controlled. The aim of the conference was to highlight recent research on how satiation and satiety can affect eating behaviour and how this understanding could potentially be utilised to help people control their weight. The day's programme included four sessions with nine expert speakers in the field of appetite control. The conference attracted 170 delegates including academics, students, health professionals and industry representatives. The conference was chaired by Professor John Blundell (University of Leeds). Professor Blundell opened the meeting by highlighting the timely topic of the conference with regard to the urgency required to deal with our burgeoning obesity rates. Obesity has a plethora of causes; it is influenced by our current obesogenic environment, as well as by eating behaviour. As this second factor is one that can potentially be modified, an understanding of how satiation and satiety can affect eating behaviour is extremely important in helping to tackle this public health problem. The first session, 'How the body communicates satiation and satiety to the brain', was presented by Bridget Benelam (BNF). Mrs Benelam gave a comprehensive introduction to satiation and satiety. Satiation is the process that prompts us to stop eating, and satiety is the sensation that lasts after eating, suppressing further energy intake for a period of time and possibly causing a decrease in energy intake at the next meal. As hunger is a barrier to reducing energy intake, being able to identify or modify foods to enhance satiation and satiety could aid weight loss. Mrs Benelam then gave details on how satiation and satiety are measured experimentally using visual analogue scales (VAS), which are the most common method used in research for self-reported measurements of appetite. VAS typically consist of a series of questions, used to provide information about different aspects of appetite, including hunger, fullness, satiety, desire to eat and prospective consumption (how much the subject feels they could eat). Mrs Benelam went onto explain that all food and drinks that we consume have an impact on satiation and satiety, so it is important to understand whether particular foods, drinks or ingredients can have consistently differing and meaningful effects on satiety and subsequent energy intake at a feasible level of consumption. However, these effects, together with internal sensations, are not the only influences on eating behaviour. People often eat when they are already satiated and may refrain from eating when they are hungry, so it is important to account for these external factors when considering the effect of satiation and satiation in the 'real world'. Factors that can affect eating behaviour include: the variety of foods offered, portion size, palatability, physical activity, distractions while eating and the presence of other people. Mrs Benelam concluded by pointing out that although satiety and satiation are part of a tightly regulated system controlling bodyweight, these mechanisms are not designed for our current environment, and the internal signals of satiety and satiation are overwhelmed by external cues to eat. The second presentation, given by Professor Steve Bloom (Imperial College London), focused on 'Satiety signalling systems'. Professor Bloom began by highlighting how most anti-obesity treatments (such as weight-loss drugs) are largely ineffective and that bariatric surgery is currently the only proven successful treatment for obesity, albeit with massive drawbacks and risks. Therefore alternative treatments have been investigated. Professor Bloom went on to explain the mechanisms involved in hypothalamic appetite control systems and gut hormones, and how they regulate appetite. He provided examples of studies showing how administering specific gut hormones can modify the effects of satiety and satiation. Studies using the gut hormones pancreatic peptide, polypeptide YY, glucagon-like peptide 1 and oxyntomodulin (OXM) have all shown that experimental administration of these hormones reduces food intake in humans to varying extents. In the next part of Professor Bloom's presentation, he discussed the potential for peptide hormones as effective drug treatments for obesity. Professor Bloom's research group discovered that OXM reduces appetite and has a more potent effect on weight loss than some of the other peptide hormones tested. Therefore OXM offers a potential new treatment for obesity and Professor Bloom's findings have since been commercialised. Professor Bloom concluded that direct administration of agonists and antagonists, gastrointestinal surgery or diets which modify endogenous gut hormone release all offer new therapeutic approaches to the treatment of obesity. In the second session, 'The effects of foods on satiation and satiety', Dr Alex Johnstone (Rowett Research Institute, Aberdeen) presented the effects of protein on satiation and satiety. Dr Johnstone described that protein has been found to be the most satiating macronutrient, independent of energy density, relative to carbohydrate and fat. Diets that have the effect of protein-induced satiety or the ability to 'fill you up' during an eating session (satiation) have created new interest as a dietary strategy (one such example being the Atkins Diet). These high-protein low-carbohydrate diets aim to reduce hunger and promote fullness, but issues regarding their safety and efficacy have been raised. Dr Johnstone provided results of studies investigating diets with different levels of protein on satiation and satiety. Short-term studies that replicated typical durations of weight loss found that increasing the percentage of energy from protein does appear effective at promoting weight loss by reducing ad libitum intake and controlling hunger. There has been recent interest in manipulating sources of protein in the diet and assessing their impact on hunger and appetite, such as supplementing a normal-protein weight-loss diet with amino acids and meat protein vs. soya protein diets. However, it is still not clear how much protein is required to maximise protein-induced satiety, or whether there is a relationship with the energy density of the diet. Dr Johnstone concluded that weight-loss studies have typically investigated high-protein diets with up to 30% of energy intake as protein together with restricted total energy intake. Dr Johnstone's final note in her presentation emphasised that our obesogenic environment makes weight gain easy and losing weight difficult and development of preventative dietary strategies to control appetite and improve health is important to assist weight control. Therefore understanding the effect of high-protein diets, meals and food products on eating behaviour remains a future challenge. The next presentation, given by Professor Rob Welch (University of Ulster), was entitled 'The effect of fibre, fibre components and other non-nutrients on satiety'. Professor Welch explained that compositional and structural factors of food affect the level of impact on satiety. Compositional factors include macronutrient balance, and the relative amounts of fibre, and other non-nutrients such as gas and water. Structural factors include gross morphology, the integrity of cellular structure in plant foods, whether the foods are solid or liquid, and the type and stability of food colloidal structures (emulsion, gels, solids or foams). Dietary fibre is the least well characterised of the major food components and fibres range from the cell walls of fruit, vegetable and cereal foods to the gum isolates that are used to stabilise a range of foods. Professor Welch gave examples of studies from early seminal work with fruits that showed both the structure imparted by fibre, and the fibre itself, can exert significant effects on satiety. More recently, this work has been extended to vegetables and to mixed meals. Dietary fibre is diverse and although the major fibre component is indigestible carbohydrate, other components range from water-soluble oligosaccharides to polysaccharides which may be insoluble in water, or which may dissolve to yield highly viscous solutions. Professor Welch showed increasing evidence that fibre components, such as fructo-oligosaccharides, can exert a number of physiological effects which can impact on satiety, decrease energy intake and decrease body mass. Professor Welch went on to describe how early studies have indicated that water, the major component of many foods on a weight basis, and air (or other gas), the major component of many foods on a volume basis, both contribute to satiety in liquid food systems. This work has since been continued with investigations into increasing volumes of solid foods with water and air, for example, foams and mousses, and into dissolved gas in carbonated beverages, and measuring their impact on satiety. Professor Welch concluded his presentation by highlighting that there is increasing evidence that the non-nutrients fibre, water and gas may be important determinants of the level of satiety influenced by different food and beverages. Dr Barbara Rolls (Pennsylvania State University) gave the last presentation in this session focusing on 'The effect of energy density on satiation and satiety'. Dr Rolls pointed out that research investigating eating behaviour focusing on macronutrient composition of foods is incomplete and could be misleading if the energy density of the diet is not considered. The topic of energy density followed on well from Professor Welch's presentation, with the concept that lowering the energy density of a food by increasing its volume, for example, with water or gas, without changing the macronutrient content, can enhance satiety and reduce subsequent energy intake at a meal. Dr Rolls provided examples of studies showing how energy density can affect satiety. These included how cognitive and visual cues relating to the volume of food and the volume of a food infused intragastrically affect satiety. However, more studies are needed to determine critical variables involved such as portion size or volume, energy content and energy density, type of food (solid, liquid and viscosity) and different macronutrient contribution. Dr Rolls also showed evidence that ad libitum intake is influenced by energy density when the proportions of macronutrients are constant. This can be explained as people tend to eat a consistent weight of food, so when the energy density of the available foods is reduced, energy intake is reduced. Dr Rolls presented findings from studies that showed the effects of energy density on satiety in adults of different weight status, sex and behavioural characteristics, as well as in 3- to 5-year-olds. The mechanisms causing the response to variations in energy density are not yet fully understood and data from controlled studies lasting more than several days are limited. Even so, long-term clinical trials indicate that the effects of energy density can be persistent. A number of clinical trials have shown that reducing the energy density of the diet by the addition of water-rich foods such as fruits and vegetables was associated with significant weight loss even when the subjects were not on restricted energy diets. Dr Rolls concluded that lowering dietary energy density can provide effective strategies for the prevention and treatment of obesity which have been illustrated in weight-loss books written by Rolls. However, there is a need for more studies to investigate the mechanisms behind the effect of lowering the energy density of the diet and to find ways to best apply these findings. This is especially important if the food industry is to effectively apply them to novel food products aimed at aiding weight loss. The third session, 'External factors that can influence satiation and satiety', began with a presentation from Professor Martin Yeomans (University of Surrey) which was titled 'The effect of palatability on satiety'. He introduced the topic by explaining that over-consumption of palatable food has been suggested as a contributing factor to the current worldwide increase in obesity rates. The implication of this is that the short-term stimulation of appetite through sensory properties of foods can override satiety and lead to overeating. Professor Yeomans presented some early work demonstrating that the manipulation of a food's palatability can affect food intake. The intake of food increased during consumption of palatable foods compared with bland or strong-flavoured food. The theoretical account behind these findings is known as 'hedonic hunger', exploring the idea that palatability effects are independent of need state. Also, that intake of palatable food items evolved as a way of maximising the use of scarce resources, thus suggesting that palatability is largely unaffected by satiety. This contrasts with a more traditional view that liking for food is a reflection of physiological need and palatability is reduced by satiety accordingly. This is known as the 'homeostatic view' and is thought to control the broader homeostatic response of the meal size consumed. Professor Yeomans followed by comparing these two theoretical positions by reviewing the evidence examining the interaction between manipulations of satiety and palatability. He illustrated that, intriguingly, evidence can be found both for reduced liking in response to reductions in appetite and conversely weaker responses to satiety cues when faced with the opportunity to consume more palatable foods. Professor Yeomans concluded from these findings that liking for foods is enhanced when the body is deprived but is not reliably reduced when sated, suggesting that the appetite system favours over-consumption when palatable foods are available. In the final part of his talk, Professor Yeomans discussed how associations between flavour and nutrients can enhance liking and in turn drive intake rather than promoting learned control of meal size. For example, high energy density food tends to be high in fat and sugar and therefore should promote increased liking; liking then enhances intake and leads to both passive and active over-consumption. The next speaker in this session was Dr Jeff Brunstrom (University of Bristol) whose talk was entitled 'The role of learning in expectations about satiation and satiety'. His research has found that humans have clear expectations about the satiety and satiation that is likely to be experienced after consuming particular foods. These expectations are extremely important because they are highly related to the amount of food (i.e. energy) that is put on the plate and, ultimately, the amount an individual consumes. Therefore to understand energy intake, the cognitive activity associated with decisions about portion size before a meal begins needs to be considered. Dr Brunstrom went on to demonstrate how, recently, techniques have been developed that allow the quantification and comparison of 'expected satiation' and 'expected satiety' across a range of foods. 'Expected satiety' is the extent to which foods are expected to stave off hunger, and 'expected satiation' is the extent to which foods are expected to deliver fullness, and both judgements are compared on a calorie-for-calorie basis. These methods have begun to allow an understanding of the basis on which these judgements are made. Findings show that rather than being governed by perceived physical size, expectations appear to be learned and refined over time. As a result, changes in expected satiety and satiation can be monitored as assessors become familiar with a novel food. Dr Brunstrom also provided evidence exploring the relative importance of expectations in decisions about portion size. Results suggest that the amount of energy that we serve on our plate is largely determined by expected satiation and that food palatability may be less important. Recent research also reveals that, calorie-for-calorie, foods differ considerably in their expected satiety and satiation which could prove very useful in weight management because foods that have high expected satiety and satiation will tend to be selected in smaller portions to reduce total energy content. To complete his presentation, Dr Brunstrom summarised the following outcomes regarding the role of learning in expectations about satiation and satiety: energy intake is often determined before a meal begins; expected satiety and satiation determines the amount of energy that we put on our plate and expected satiety and satiation is learned over time. In the last session, 'How can we use satiation and satiety to help weight control?', the penultimate speaker of the day was Dr James Stubbs (Slimming World) who talked about 'Practical measures to enhance satiety and control weight'. Dr Stubbs reiterated that the secular trend of increased obesity prevalence is worsening and the health consequences to society will be a major burden to governments, health professionals, the food industry and the public for a long time to come. To tackle this problem, despite the current interest in genetics and obese phenotypes, current obesity research has so far failed to deliver any serious practical solutions that can be implemented as public health policy. Dr Stubbs stressed that the abundance of ideas and mechanisms for how to control weight are impractical unless they can be communicated in a way that people will appreciate and can apply to everyday living. Dr Stubbs continued by explaining the evidence behind possible practical solutions to successful weight loss. He introduced the concept of energy gaps, which are the energy deficits required in the diet associated with control of weight. The first energy gap identified is that of a reduction in energy intake by approximately 100 kcal/day, which has been suggested to protect 90% of the population from weight gain. There are two further energy gaps; the second is the energy deficit required for overweight people to lose the government recommendations of 0.5–1 kg/week, which totals approximately 250–500 kcal/day. The third energy gap is the energy deficit that people need to maintain weight once bodyweight has been lost. Although the value of this energy gap is less clear, studies indicate that people need to sustain a 300–600-kcal/day energy deficit, relative to when they were obese, to maintain weight loss. These energy gaps demonstrate why it is relatively easy to prevent weight gain, slightly harder to lose weight and difficult to maintain weight loss. Dietary approaches based on satiety have been effective at dealing with the first two energy gaps but have not been all together successful in overcoming the third energy gap. As a result, many people who lose weight regain it. Therefore weight-loss strategies need to concentrate on the maintenance of long-term weight loss through lifelong modification of diet and lifestyle. Dr Stubbs followed by recognising that we are now in a position to integrate several aspects of diet composition and their effect on satiety with the aim to optimise practical weight loss and weight-management strategies. This is because individual dietary approaches, for example, high-protein or fat reduction diets, have been largely limited in long-term efficacy. Dr Stubbs revealed that by encouraging people to eat more of the least energy dense foods and less of the higher energy dense foods, they can eat more and lose more weight. However, in practical terms, dietary modifications need to be considered in the context of other behaviours, and lifestyle changes that increase physical activity are crucial for weight-loss maintenance. Evidence suggests that the greater number of weight control behaviours employed by the individual, the greater the weight loss achieved. In Dr Stubbs' conclusion, he emphasised that to develop effective practical measures for weight control, we need to focus on personalised behavioural solutions to maintain a healthy bodyweight for that individual. Rather than match people to treatments, we need to provide a range of approaches to enable people to choose the solutions that best suit their individual lifestyle needs. Furthermore, we need to continually support them in achieving sustained lifestyle change with an infrastructure of psychological and group support. The final speaker of the day was Dr Jason Halford (University of Liverpool). He concentrated on 'Opportunities for industry – satiety enhancing products and health claims'. Dr Halford explained how mechanisms involved in satiety and satiation have provided the food industry with numerous potential targets for manufacturing products aimed at weight control. These include some of the biopsychological processes that proceed, sustain, terminate and inhibit further consumption. Of particular interest are the nutrient-stimulated signals that stimulate hunger or satiety indirectly through changes in gastric motility and directly through signals relayed to the central nervous system. Dr Halford provided examples of the wide range of weight-control products that are available around the world, many of which claim to act on appetite. However, the evidence behind the efficacy of some of these products is limited and not all make realistic claims to the consumer. As a result, increasing scrutiny from various regulatory authorities ensures that advertised health claims must be supported by robust evidence. This process was implemented in 2008 under European Union regulation on nutrition and health claims made on food. In recent years, a number of novel satiety enhancing ingredients have been formulated and are available to food manufacturers. These include novel fats and fibres, but it is unclear from studies whether these ingredients produce unique effects on appetite distinct from closely related nutrients. In addition, such ingredients are used in different dose regimes and food matrices and it is uncertain if satiety enhancing effects persist in these differing product formulations. Dr Halford then disclosed results of studies that combined protein and fibre, which have created another opportunity for developing products to aid appetite control. These products have produced changes in appetite and energy intake in experimental situations. However, whether effects on appetite can be sustained over time is unclear and whether these products can produce long-term weight management benefits to consumers remains to be shown. To conclude, Dr Halford pointed out some limitations to these novel products, which included the problematic task of establishing their efficacy in free-living situations, outside laboratory conditions, where appetites may be more readily stimulated and control overwhelmed. Furthermore, consumer acceptability remains a major obstacle to weight-control product development. The chairman, Professor Blundell, closed the conference by thanking the speakers for presenting their interesting research on this timely subject, which should prove to be immensely useful in helping to develop future strategies to combat the current obesity pandemic. The BNF has produced a number of useful resources promoting the key messages identified by the Briefing Paper, including top tips, a podcast, recipes and a 'Feed yourself fuller' chart which displays the differing energy density foods (see http://www.nutrition.org.uk). The Briefing Paper was published in the June 2009 issue of Nutrition Bulletin (Benelam 2009).