Cognitive factors in the dietary response of restrained and unrestrained eaters to manipulation of the fat content of a dish

Remembering to eat: hippocampal regulation of meal onset

A wide variety of species, including vertebrate and invertebrates, consume food in bouts (i.e., meals). Decades of research suggest that different mechanisms regulate meal initiation (when to start eating) versus meal termination (how much to eat in a meal, also known as satiety). There is a very limited understanding of the mechanisms that regulate meal onset and the duration of the postprandial intermeal interval (ppIMI). In the present review, we examine issues involved in measuring meal onset and some of the limited available evidence regarding how it is regulated. Then, we describe our recent work indicating that dorsal hippocampal neurons inhibit meal onset during the ppIMI and describe the processes that may be involved in this. We also synthesize recent evidence, including evidence from our laboratory, suggesting that overeating impairs hippocampal functioning and that impaired hippocampal functioning, in turn, contributes to the development and/or maintenance of diet-induced obesity. Finally, we identify critical questions and challenges for future research investigating neural controls of meal onset.

Consumption with large sip sizes increases food intake and leads to underestimation of the amount consumed

BACKGROUND

A number of studies have shown that bite and sip sizes influence the amount of food intake. Consuming with small sips instead of large sips means relatively more sips for the same amount of food to be consumed; people may believe that intake is higher which leads to faster satiation. This effect may be disturbed when people are distracted.

OBJECTIVE

The objective of the study is to assess the effects of sip size in a focused state and a distracted state on ad libitum intake and on the estimated amount consumed.

DESIGN

In this 3×2 cross-over design, 53 healthy subjects consumed ad libitum soup with small sips (5 g, 60 g/min), large sips (15 g, 60 g/min), and free sips (where sip size was determined by subjects themselves), in both a distracted and focused state. Sips were administered via a pump. There were no visual cues toward consumption. Subjects then estimated how much they had consumed by filling soup in soup bowls.

RESULTS

Intake in the small-sip condition was ∼30% lower than in both the large-sip and free-sip conditions (P<0.001). In addition, subjects underestimated how much they had consumed in the large-sip and free-sip conditions (P<0.03). Distraction led to a general increase in food intake (P = 0.003), independent of sip size. Distraction did not influence sip size or estimations.

CONCLUSIONS

Consumption with large sips led to higher food intake, as expected. Large sips, that were either fixed or chosen by subjects themselves led to underestimations of the amount consumed. This may be a risk factor for over-consumption. Reducing sip or bite sizes may successfully lower food intake, even in a distracted state.

'Expected satiety' changes hunger and fullness in the inter-meal interval

Previously, we have shown that foods differ markedly in the satiety that they are expected to confer (compared calorie-for-calorie). In the present study we tested the hypothesis that 'expected satiety' plays a causal role in the satiety that is experienced after a food has been consumed. Before lunch, participants (N=32) were shown the ingredients of a fruit smoothie. Half were shown a small portion of fruit and half were shown a large portion. Participants then assessed the expected satiety of the smoothie and provided appetite ratings, before, and for three hours after its consumption. As anticipated, expected satiety was significantly higher in the 'large portion' condition. Moreover, and consistent with our hypothesis, participants reported significantly less hunger and significantly greater fullness in the large-portion condition. Importantly, this effect endured throughout the test period (for three hours). Together, these findings confirm previous reports indicating that beliefs and expectations can have marked effects on satiety and they show that this effect can persist well into the inter-meal interval. Potential explanations are discussed, including the prospect that satiety is moderated by memories of expected satiety that are encoded around the time that a meal is consumed.

Impact of restraint and disinhibition on PYY plasma levels and subjective feelings of appetite

The impact of eating behaviours on circulating levels of appetite-regulating hormones remains largely unknown. The aims of this study were to assess the role of restraint and disinhibition on fasting/postprandial peptide YY (PYY) plasma levels and subjective feelings of appetite in normal-weight individuals and to determine whether the effect was energy load dependent. 33 participants (12 men) were classified as restrained/unrestrained and low/high in disinhibition based on Three Factor Eating Questionnaire-18R and Dutch Eating Behaviour Questionnaire. The impact of restraint/disinhibition on PYY plasma levels and feelings of appetite was measured, after a 500kcal and 1000kcal breakfast, using a randomised crossover design. Restraint did not impact on either fasting or postprandial PYY plasma levels, but participants with high disinhibition had a tendency towards a blunted postprandial PYY response. Moreover, restrained eaters reported lower ratings of prospective food consumption postprandially, and a tendency towards higher fullness/lower hunger. In conclusion, circulating PYY is unaffected by restrained eating behaviour, despite being associated with increased fullness and reduced hunger in the fed state. High levels of disinhibition tend to be associated with a blunted PYY response and this may contribute towards the susceptibility to overconsumption and increased risk of weight gain characteristic of this trait.

Tasting fat: Cephalic phase hormonal responses and food intake in restrained and unrestrained eaters

Restrained eaters exhibit strict cognitive control over their food intake, primarily by limiting intake of high-fat foods. Earlier studies indicate a relationship between dietary restraint and cephalic phase insulin release, which is hypothesized to influence hunger and food intake. To compare cephalic phase hormonal responses to high- and low-fat stimuli and determine if the sensory experience of tasting fat alters hormonal responses and influences subsequent food intake in restrained and unrestrained eaters, normal weight women classified as unrestrained (n=11) or restrained (n=11) eaters were tested under 3 conditions: (1) fasting, (2) sham-feeding a non-fat cake, and (3) sham-feeding a high-fat cake. Following an overnight fast, arterialized venous blood was drawn prior to and for 30 min immediately following a 3-min sham feed. Plasma samples were analyzed for insulin, glucose, glucagon and pancreatic polypeptide (PP). Subjects were subsequently given a selection of high-fat and low-fat foods and allowed to select what they wished to eat. Cephalic phase PP was significantly greater following oral sensory stimulation by the high-fat food (205.4+/-83.6) compared to the fasting control (11.1+/-38.8, p=0.04). No significant differences in hormonal responses to the food stimuli were found between restrained and unrestrained eaters but the restrained eaters consumed more food after the high-fat condition (p<0.05) relative to the fasted condition and compared to the unrestrained group (p<0.05). In conclusion, the sensory experience of tasting fat increases food intake in restrained eaters and increases vagal efferent activity compared to a non-fat food in both populations.

Effects of fat content on fat hedonics: cognition or taste?

Understanding and perhaps overriding preferences for fat is important, given the relationship between higher dietary fat consumption and poorer health. We have examined the roles of potential mechanisms for differences in fat preference: actual fat content and expected fat content. The subjects were women (n=192, ages=50-69) recruited to a study of low-fat dietary change. Subjects were randomized to one of the four cells: participants received either a high- or low-fat milkshake at baseline, and half of each group was told that their milkshake was low in fat and the other half high in fat. Women who received a high-fat milkshake consumed more grams than women who received a low-fat milkshake. Women who expected low-fat shakes reported liking them more than those who expected high-fat milkshakes. These data indicate that both physiology and cognition play a role in determining consumption of high- and low-fat foods.

Does nutrition information about the energy density of meals affect food intake in normal-weight women?

This study investigated whether the energy density of foods affected energy intake when subjects were informed about the energy density of their meals. Forty normal-weight women ate breakfast, lunch, and dinner in the laboratory on three separate days. The entrée at each meal was varied in energy density to be either 1.25, 1.50, or 1.75 kcal/g (5.23, 6.28, or 7.32 kJ/g), but was held similar in macronutrient composition and palatability. On each day, the entrées at all three meals had the same energy density. All entrées were consumed ad libitum. Subjects were assigned to one of two groups. Subjects in the information group received a nutrition label with each meal, which showed the energy density of the entrée. Subjects in the no-information group did not receive any nutrition information. The results revealed that subjects in both groups had the same pattern of food intake across the three levels of energy density. Energy density significantly affected energy intake; subjects in both groups combined consumed 22% less energy in the condition of low energy density than in the condition of high energy density (p < 0.0001). These findings show that energy density can have a significant influence on energy intake, even when individuals are informed about the energy density of their meals.

The actual, but not labelled, fat content of a soup preload alters short-term appetite in healthy men

The effects of the actual and labelled fat content of a soup preload on appetite at a test meal 30 min later were assessed in 16 healthy men. Each participant ate lunch on four occasions, combining two levels of fat energy (Low, 265 kJ or High, 1510 kJ) and two types of label (Low-fat or High-fat), presented as fictitious soup brand names. Preliminary work established that the Low-fat labels produced an expectation of reduced fat content and lower anticipated hedonic ratings, whereas the High-fat labels generated expectations of a high-fat content and above average hedonic ratings. These expectancies were confirmed in the main experiment, with the soups labelled as high fat rated as both more pleasant and creamy than those labelled low-fat, independent of actual fat content. However, intake at the test meal was unaffected by the preload label, but instead reflected the actual fat (hence, energy) content of the soup, with significantly lower food intake after the high-fat soup regardless of the food label. Rated hunger was lower, and fullness higher, at the start of the meal after the high-fat preloads regardless of how they were labelled, while the pattern of appetite change during the test meal was unaffected by preload. These results suggest that realistic food labels can modify the immediate experience of a consumed food, but do not alter appetite 30 min later in healthy men.

The influence of recipe modification and nutritional information on restaurant food acceptance and macronutrient intakes

OBJECTIVE

To examine the influences of nutritional information and consumer characteristics on meal quality expectations, food selection and subsequent macronutrient intakes of consumers offered a reduced-fat option in a restaurant.

DESIGN

A target, full-fat (FF) main restaurant meal option was developed in a version substantially reduced in fat and energy (RF). Restaurant patrons were randomly placed into one of four treatment groups varying in provision of menu information about the target dish, and the actual version of that dish served (if ordered). A full-fat blind (FFB) control group was given no nutritional information in the menu and was served the FF version. The other three groups were all served the modified RF version: (i) reduced-fat blind (RFB), who were given no nutritional information; (ii) reduced-fat informed (RFI), who were given nutritional information; and (iii) reduced-fat informed with details (RFID), who were given the same nutritional information plus recipe modification details. Subjects rated their expected and actual liking, the pleasantness of taste, texture and appearance of the dish, how well the dish matched their expectations, and the likelihood of purchase again. Additional measures included the other dish selections, sociodemographic and attitudinal information.

SETTING

A silver service (training) restaurant.

SUBJECTS

Members of the public (n = 279) consuming meals in the restaurant.

RESULTS

The presence of nutritional information on the menu did not significantly increase subsequent intakes of energy and fat from the rest of the meal, and did not significantly influence sensory expectations or post-meal acceptance measures (which also did not differ between the FF and RF versions). Consumer characteristics relating to fat reduction attitudes and behaviours were significantly related to the selection of different dishes.

CONCLUSIONS

Provision of RF alternatives in a restaurant can have significant positive dietary benefits. Menu nutritional information did not affect measures of meal acceptance. Further studies should identify which types of information formats might be most effective in enhancing the selection of 'healthy' options.

Modalities of the food intake-reducing effect of sibutramine in humans

Sibutramine is a serotonin and noradrenaline reuptake inhibitor exerting a weight reducing effect partly via its anorectic properties. We investigated the effects of 15 mg sibutramine on objective (intake) and subjective (sensations) parameters of eating behavior in 24 young male subjects. At 0830 h subjects took either placebo or sibutramine in a counterbalanced order, followed by a fixed amount of breakfast. Intake was covertly recorded in the laboratory until the dinner meal, and then until the next morning using diary reports. Sibutramine induced a highly significant reduction in energy (1304 kJ, p < 0.001), protein (294 kJ, p < 0.001), fat (414 kJ, p < 0.01), and carbohydrate (CHO, 594 kJ, p < 0.001) intakes compared to placebo. This reduction was further enhanced when 24-h intake was analyzed (1601 kJ, p < 0.001). The effect of sibutramine occurred mainly at lunch (637 kJ, p = 0.005). Throughout the test day the number of items consumed and the weight of food were reduced by sibutramine (1.6, p < 0.01 and 222 g, p < 0.001, respectively), whereas energy density was not changed. Meals minus dessert items were the most altered by sibutramine. A specific CHO reduction was found in the dinner meal, although the proportions of macronutrients in total daily energy intake were not changed by sibutramine. Hunger ratings began to be lower than placebo 240 min after sibutramine. These results show that a single dose of sibutramine in lean humans induces a potent reduction in intake, and that its action is modulated according to the time of occurrence and the structure of the meal.