David J. Mela

Appetite control: methodological aspects of the evaluation of foods

This report describes a set of scientific procedures used to assess the impact of foods and food ingredients on the expression of appetite (psychological and behavioural). An overarching priority has been to enable potential evaluators of health claims about foods to identify justified claims and to exclude claims that are not supported by scientific evidence for the effect cited. This priority follows precisely from the principles set down in the PASSCLAIM report. The report allows the evaluation of the strength of health claims, about the effects of foods on appetite, which can be sustained on the basis of the commonly used scientific designs and experimental procedures. The report includes different designs for assessing effects on satiation as opposed to satiety, detailed coverage of the extent to which a change in hunger can stand alone as a measure of appetite control and an extensive discussion of the statistical procedures appropriate for handling data in this field of research. Because research in this area is continually evolving, new improved methodologies may emerge over time and will need to be incorporated into the framework. One main objective of the report has been to produce guidance on good practice in carrying out appetite research, and not to set down a series of commandments that must be followed.

Eating for pleasure or just wanting to eat? Reconsidering sensory hedonic responses as a driver of obesity.

Pleasure from foods can stimulate non-homoeostatic eating, and might therefore also potentially contribute toward obesity. However, obesity is not reliably associated with heightened hedonic responses to foods. This apparent discrepancy may reflect the differentiation between liking and wanting. Supporting this, behavioural and neurophysiological data on responsiveness to food-related cues indicate that obesity may be associated with increased motivation for food consumption, without necessarily any greater explicit pleasure derived from the orosensory experience of eating. This distinction may have important implications for further research, and applications in commercial and public health approaches to modifying energy intakes.

Differences in health and taste attitudes and reported behaviour among Finnish, Dutch and British consumers: a cross-national validation of the Health and Taste Attitude Scales (HTAS).

The Health and Taste Attitude Scales (HTAS) developed by Roininen, Lähteenmäki and Tuorila in 1999 measure the importance of health and taste aspects of foods in the food choice process. These multi-item scales consist of sets of statements, ranging from strongly disagree to strongly agree, which further divide into three Health (General health interest, Light product interest and Natural product interest) and three Taste (Craving for sweet foods, Using food as a reward and Pleasure) sub-scales. Finnish (N=467), Dutch (N=477), and British (N=361) respondents completed a questionnaire which contained four components: the HTAS, a separate paper and pencil task of choosing a food for a snack; pleasantness, healthiness and frequency of consumption of eight foods; and the Restraint Eating Scale of the Dutch Eating Behaviour Questionnaire (DEBQ). The latter three components were included in order to validate various aspects of the HTAS. The factor structure of HTAS was found to be equal in all three countries. However, there were some minor differences in factor loadings among countries, e.g. the Natural product interest and Pleasure sub-scale items had lower factor loadings in the UK than in Finland and The Netherlands. Finnish respondents had the most positive attitude towards light products. Dutch and British respondents scored higher on all Taste sub-scales than their Finnish counterparts. Respondents health-related attitudes were good predictors of their healthy food choices in the snack task and self-reported consumption. Two of the Taste sub-scales (Craving for sweet foods and Using food as a reward) predicted well respondents self-reported consumption of, for example, full-fat chocolate bars. All the Health and two of the Taste sub-scales proved to be useful tools for characterizing consumer attitudes within and between countries.

Sensory assessment of fat content in fluid dairy products.

It is unclear what stimulus properties and sensory systems contribute to the discrimination of fat content in foods. Fluid dairy products containing 0.5 to 36% fat were rated on category scales for fat content, creaminess, and pleasantness under various conditions. In the first experiment, perceived fat content of the stimuli was not changed from normal conditions when visual and olfactory inputs were removed. In a second experiment, the stimuli were altered by the addition of a textural agent, such that their viscosities were all approximately equivalent. Elimination of olfactory input again had no effect on ratings of fat content. Addition of a textural agent greatly enhanced the apparent fat content of the lower fat samples, though it did not fully compensate for the perceived differences amongst the stimuli. These experiments strongly support the concept that perceptions of fat content in these products is largely attributable to textural properties, such as viscosity, sensed within the oral cavity.

Does low-energy sweetener consumption affect energy intake and body weight? A systematic review, including meta- analyses, of the evidence from human and animal studies

By reducing energy density, low-energy sweeteners (LES) might be expected to reduce energy intake (EI) and body weight (BW). To assess the totality of the evidence testing the null hypothesis that LES exposure (versus sugars or unsweetened alternatives) has no effect on EI or BW, we conducted a systematic review of relevant studies in animals and humans consuming LES with ad libitum access to food energy. In 62 of 90 animal studies exposure to LES did not affect or decreased BW. Of 28 reporting increased BW, 19 compared LES with glucose exposure using a specific ‘learning’ paradigm. Twelve prospective cohort studies in humans reported inconsistent associations between LES use and body mass index (−0.002u2009kgu2009m−2 per year, 95% confidence interval (CI) −0.009 to 0.005). Meta-analysis of short-term randomized controlled trials (129 comparisons) showed reduced total EI for LES versus sugar-sweetened food or beverage consumption before an ad libitum meal (−94u2009kcal, 95% CI −122 to −66), with no difference versus water (−2u2009kcal, 95% CI −30 to 26). This was consistent with EI results from sustained intervention randomized controlled trials (10 comparisons). Meta-analysis of sustained intervention randomized controlled trials (4 weeks to 40 months) showed that consumption of LES versus sugar led to relatively reduced BW (nine comparisons; −1.35u2009kg, 95% CI –2.28 to −0.42), and a similar relative reduction in BW versus water (three comparisons; −1.24u2009kg, 95% CI –2.22 to −0.26). Most animal studies did not mimic LES consumption by humans, and reverse causation may influence the results of prospective cohort studies. The preponderance of evidence from all human randomized controlled trials indicates that LES do not increase EI or BW, whether compared with caloric or non-caloric (for example, water) control conditions. Overall, the balance of evidence indicates that use of LES in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water.

Short- and long-term effects of changes in pleasantness on food intake.

This study concerns the effects of pleasantness on ad libitum food intake, liking and appetite over 5 successive days. Pleasantness was manipulated by varying the salt level in bread. Thirty-five students consumed ad libitum sandwiches for lunch, made with bread individually perceived as low, medium or high in pleasantness, in a balanced cross-over design. Pleasantness and desire-to-eat the sandwich were rated at first bite, after the consumption of each sandwich and at the end of the lunch. Fullness was rated just before and at several intervals after lunch. On the first day, the students ate less of the least pleasant bread than of the medium and most pleasant bread. On the fifth day, however, consumption of all breads was similar. For the least pleasant bread, energy intake at lunch, desire-to-eat and fullness, all increased over days, whereas these variables remained constant for the medium and most pleasant bread. Mean pleasantness ratings for all breads remained unaltered across the days. We conclude that, with repeated exposure, the desire-to-eat, fullness and intake of a less preferred food can increase over time. Thus, the relationship between pleasantness and food intake changes over this period.

Sensory Assessment of Fat Content: Effect of Emulsion and Subject Characteristics

This work examines some of the fundamental stimulus properties contributing to the perception and discrimination of fat content in foods. In an initial experiment, oil-in-water (O/W) emulsions were prepared with 0, 5, 10, ..., 40, 45, and 50% sunflower oil (SUN) and homogenized at pressures of 100 and 300 bar. These were rated for fat content and smoothness on 9-point category scales. There were significant effects of fat concentration and processing pressure. Higher pressures, associated with a decreased fat particle size/number ratio, generated a slightly enhanced perception of fat content. In a second experiment, O/W emulsions were prepared with 0, 12, 24, 36, and 48% fat at 100 and 300 bar, from two oils differing in fat saturation: SUN and Hycoa 5 (HY5, a highly saturated commercial cocoa butter substitute). The results indicate significant main and interactive effects of fat type and concentration, but no significant effect of processing pressure were seen in this experiment. HY5 emulsions had a substantially greater measured viscosity and were judged higher in fat content than those prepared from SUN, particularly at higher fat levels. Analyses indicate a significant independent contribution of fat concentration to perceived fat content, beyond increased viscosity. There were no consistent main or interactive effects of subject age or body composition on judgments of fat content.

Potential benefits of satiety to the consumer: scientific considerations.

Foods and dietary patterns that enhance satiety may provide benefit to consumers. The aim of the present review was to describe, consider and evaluate research on potential benefits of enhanced satiety. The proposal that enhanced satiety could only benefit consumers by a direct effect on food intake should be rejected. Instead, it is proposed that there is a variety of routes through which enhanced satiety could (indirectly) benefit dietary control or weight-management goals. The review highlights specific potential benefits of satiety, including: providing appetite control strategies for consumers generally and for those who are highly responsive to food cues; offering pleasure and satisfaction associated with low-energy/healthier versions of foods without feeling deprived; reducing dysphoric mood associated with hunger especially during energy restriction; and improved compliance with healthy eating or weight-management efforts. There is convincing evidence of short-term satiety benefits, but only probable evidence for longer-term benefits to hunger management, possible evidence of benefits to mood and cognition, inadequate evidence that satiety enhancement can promote weight loss, and no evidence on which consumers would benefit most from satiety enhancement. The appetite-reducing effects of specific foods or diets will be much more subtle than those of pharmaceutical compounds in managing hunger; nevertheless, the experience of pharmacology in producing weight loss via effects on appetite suggests that there is potential benefit of satiety enhancement from foods incorporated into the diet to the consumer.

Effects of learned flavour cues on short-term regulation of food intake in a realistic setting

The present study examined the effects of repeated midmorning consumption of novel-flavoured low- and high-energy yoghurt drinks on subsequent energy intake at lunch in 69 adults under actual use conditions. Subjects consumed 200 ml of low- and high-energy yoghurt drinks (67 and 273 kcal/200 ml, respectively), with 20 exposures to each drink on alternate days. Analyses focused on the development of compensation for the differences in energy content of the beverages, due to learned satiety. Results revealed incomplete energy compensation for the beverages, both at first exposure and also after 20 exposures. Relative to the no-yoghurt condition, energy intake compensation (+/-S.E.M.) averaged 39+/-36% for the low-energy yoghurt and 17+/-9% for the high-energy version, with no evidence of any change in compensation with repeated exposures. When the flavours of the yoghurt drinks were covertly switched after 20 exposures, subjects increased their energy intake after the high-energy yoghurt drink containing the flavour that was previously coupled with the low-energy yoghurt drink. Vice versa, however, when subjects switched to the low-energy yoghurt drink containing the high-energy flavour, subjects ignored the flavour cue and ate the same lunch size regardless of the energy in the yoghurt drink. We conclude that adults do not readily acquire accurate conditioned adjustments for the energy content in food after repeated experience with the food in free-living natural-eating conditions.

Relationships of consumer characteristics and food deprivation to food purchasing behavior.

A large part of domestic food intake may be determined by retail food purchase behavior, and it is commonly believed that this may be significantly influenced by the shoppers state of food deprivation. In the present study, 198 subjects recruited just prior to shopping at a large supermarket completed questionnaires eliciting information on demographic and situational variables, along with measures of time since last eating (TSLE), hunger, and dietary restraint. Upon leaving the store, subjects provided investigators with itemized receipts, having first identified all unintended purchases. There were no consistent main effects of TSLE, self-reported hunger, dietary restraint scores, or relative body weight on the number or cost of total, intended, and unintended food and nonfood purchases. However, there were significant interactions of weight status and measures of food deprivation upon measures of food purchasing. Although normal-weight subjects tended to increase their food purchases with food deprivation, the number and cost of food items fell markedly with extended food deprivation among overweight subjects. These effects were largely specific to food (i.e., generally not observed for nonfood purchases), but showed no consistent associations with unintended purchases or with particular foods or food groups. Higher dietary restraint and relative body weight were associated with lower reported hunger ratings, but not differences in mean TSLE, or other subject characteristics. These results run directly counter to common beliefs and recommendations for weight control and dieting, but support earlier work indicating that the food purchasing behaviors of normal-weight and overweight individuals are differently affected by food deprivation.