Palatability and foraging cost interact to control caloric intake.

The combined effects of meal cost and food flavor on meal size were studied with a method that avoided the covariation of nutrient composition and caloric density with palatability. As rats (Rattus norvegicus) drank flavored fluids (unpalatable 0.05% sucrose octaacetate [SOA], neutral 0.05% saccharin, and palatable 2% Polycose?+?0.2% saccharin [P?+?S]), liquid diet was infused intragastrically. Relative to saccharin, rats with free access ate 10% more calories in larger meals while consuming P?+?S and initially ate fewer calories in smaller but more frequent meals while drinking SOA. Other rats lever-pressed to begin meals, which halved meal number and doubled meal size relative to the free-access group. Although foraging rats also ate larger P?+?S meals and smaller SOA meals, the changes did not affect total intake. Without the usual differential postingestive effects of foods that differ in palatability, making food more costly blunts rats' response to its flavor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unlearned appetite controls: Watersnakes (Nerodia) take smaller meals when they have the choice.

Studies of appetite in mammals emphasize that meal size is learned, but lactation and parental care constrain testing of naive individuals. Neonatal reptiles, in contrast, are self-sufficient foragers. The authors examined the effect of prey size on meal size in primivorous (at first feeding) northern watersnakes (Nerodia sipedon). When offered an excess of small prey (2%-20% of snake mass), neonates ate significantly smaller meals (M = 23.5% of snake mass) than when offered a single huge item (range = 32%-55%). The authors conclude that (a) the taking of smaller meals is not a learned effect, (b) there may be a satiety threshold for meal size rather than a target, (c) oropharyngeal stimuli may provide satiety cues, and (d) huge meals may have fitness costs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of palatability and feeding conditions on digestive functions in rats

OBJECTIVE: Information concerning various post prandial gastrointestinal functions modulated by taste stimulation is rather limited. Thus, effects of different types of palatability and feeding condition on digestive functions were studied. METHODS: Male Sprague-Dawley rats were divided into two different feeding groups, meal feeding and ad libitum. In meal feeding, the daily feeding period was shortened gradually and was restricted eventually only 3 hours. In ad libitum feeding, food was freely available for 24 hours until experiment. After each rat in both feeding groups was fed 8.29 mM saccharin or 1.28 mM quinine flavored diet as a taste stimulant for 15 minutes, changes of gastric and intestinal nitrogen and pH and pancreatic amylase activities were compared with meal feeding vs ad libitum feeding. RESULTS: In meal feeding, no difference was observed between before and after taste stimulation or between saccharin and quinine flavored diets on gastric and intestinal nitrogen contents, pH in the stomach and in the small intestine, and amylase activity. On the other hand, in ad libitum feeding, intestinal nitrogen contents tended to stagnate until 60 minutes after tasting quinine, although there was little difference between saccharin and quinine diets on gastric nitrogen contents. Gastric juice was hardly secreted before tasting (pH 6.2) and then pH in the stomach changed to become more acid following taste stimulation. Although amylase secreted in small intestine was hardly secreted before tasting, activities after tasting saccharin were increased immediately and lasted until 120 minutes. Amylase activity in rats fed the quinine diet, however, showed slower increase and faster recovery than that in rats fed the saccharin diet. CONCLUSIONS: The results confirmed that various postingestive functions after taste stimulation depend on feeding conditions and it suggests that the ad libitum feeding condition is more appropriate than meal feeding on the experiment related to gustatory response.     

Effects of neuropeptide Y on feeding microstructure: Dissociation of appetitive and consummatory actions.

The effects of intracerebroventricular application of Neuropeptide Y (NPY) on licking microstructure for sucrose, saccharin, and water solutions were evaluated. In Experiment 1, NPY increased meal size for three sucrose concentrations (0.03 M, 0.3 M, and 1.0 M) by increasing licking burst number but not size and by extending meals more than four-fold in duration with a slow, sustained rate of ingestion in late phases of the meal. Results are consistent with the interpretation that NPY suppressed inhibitory postingestive feedback. Experiment 2 supported this conclusion. NPY significantly increased the number of meals initiated for water, 0.1% saccharin, and 1.0 M sucrose solutions, but meal size was only increased for 1.0 M sucrose. Therefore, NPY also increased appetitive feeding behaviors, but its consummatory effects were limited to caloric solutions. The results are discussed with regard to their potential to explain current discrepancies in the literature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Timing of Meals.

In most individuals, food intake occurs as discrete bouts or meals, and little attention has been paid to the factors that normally determine when meals will occur when food is freely available. On the basis of experiments using rats, the authors suggest that when there are no constraints on obtaining food and few competing activities, 3 levels of interacting controls normally dictate when meals will start. The first is the genetically determined circadian activity pattern on which nocturnal animals tend to initiate most meals in the dark. The second is the regularly occurring changing of the light cycle: These changes provide temporal anchors. The third relates to the size of the preceding meal, such that larger meals cause a longer delay until the onset of the next meal. Superimposed on these 3 are factors related to learning, convenience, and opportunity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned flavor preferences based on delayed caloric consequences.

In four experiments we showed that rats prefer a flavor associated with a delayed edible consequence if the delayed consequence contains calories; the greater the number of calories, the greater the preference. We obtained conditioned preferences with delayed consequences of dextrose plus quinine, 8% polycose, 8% sucrose, 10 g of high fat mash, and 14 g of lab chow. No conditioned preferences were obtained with delayed consequences of saccharin, 10 g of low fat mash, 1% polycose, or 1% sucrose. Thus, it seems that flavor preferences based on delayed caloric consequences occur only if there are appreciable calories in the consequence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Isolation and analysis of a gene bbe1 encoding the berberine bridge enzyme from the California poppy Eschscholzia californica

Rats experience anorexia and reduction or cessation in growth after being provided a zinc-deficient diet. While zinc deficient, intake levels may be reduced 50% or more compared to control rats. In the present report, diurnal food intake patterns of male Sprague-Dawley rats were measured during zinc deficiency. In Study 1, rats consuming a modified AIN-93 diet were tested during the dark phase using an automated food weighing system. In zinc-deficient animals (Zn-), the onset of the first meal of the dark phase was delayed compared to zinc-adequate rats (Zn+; 106+/-47 vs. 23+/-5 min; p<0.05) and the number of meals consumed during the dark phase was reduced in Zn- vs. Zn+ rats (3.9+/-0.5 vs 7.1+/-0.4; p<0.05). In Study 2, diurnal food intake patterns were tested using a three-choice macronutrient self-selection paradigm of carbohydrate-, protein-, and fat-containing diets made deficient or adequate in zinc (1 or 30 mg Zn/kg diet). Food intake was recorded in the early-, mid-, late-dark period (4 h each) and light period (12 h). Carbohydrate intake was 70% of total intake of both Zn+ and Zn- rats during the first 5 days, but decreased significantly to 50% in the Zn- group during the last 5 days. Fat intake increased significantly in the Zn- group during the last 5 days. This increase was the result of 4 of 15 Zn- rats increasing their intake of fat significantly. Results of this study indicate that zinc status alters dark phase and macronutrient selection patterns by delaying consumption of the initial meal of the dark phase, reducing the average meal number and by changing the dominant macronutrient preference of some Zn- rats.     

Ovariectomy and estradiol affect postingestive controls of sucrose licking

Ovariectomy (OVX) has been shown to increase, and estradiol replacement to decrease, meal size in rats. Because little is known about how estradiol influences meals, we conducted two experiments to examine the effects of OVX and beta-estradiol 3-benzoate (EB) replacement on the microstructure of licking behavior. In both experiments, patterns of licking were analyzed in adult female Sprague-Dawley rats during an 0.8 M sucrose test meal. In Experiment 1, meal microstructure was determined preOVX and 10-12 days postOVX. Rate of licking following OVX was not changed during min 1 of the meal, but was significantly faster during min 2-4 of the meal (p < 0.03). The numbers of bursts (runs of licks separated by 250-500 ms) and numbers of clusters (runs of licks separated by > 500 ms) were significantly increased during min 2-4 (p < 0.05). In Experiment 2, OVX rats received EB replacement. Rate of licking after EB replacement was not changed during min 1 of the meal, but was significantly slower during the remainder of the meal (min 2-4, min 5-7, and min 8-10). Burst size, cluster size, and interburst interval were less after EB replacement during min 5-7 of the test meal (all p < 0.05). Because both OVX and EB replacement failed to alter the rate of licking during min 1, estrogen did not appear to alter the palatability of sucrose. OVX and EB replacement did appear to affect a postingestive mechanism(s) that is engaged within 2-4 min of meal onset.     

Effects of ovariectomy on meal pattern in the albino rat.

In a study with 24 female albino Sherman rats, it was found that after ovariectomy most Ss increased food intake while continuing to eat discrete meals. Meal size increased in ovariectomized Ss, whereas meal frequency decreased. It is suggested that ovariectomy impairs the onset of satiety during a meal but not the ability to regulate total intake through modification of intermeal interval. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Energy density of foods affects energy intake in normal-weight women

This study examined the effect of energy density, independent of fat content and palatability, on food and energy intakes. With use of a within-subjects design, normal-weight women (n = 18) were provided with meals for 2 d during each of three test sessions. During lunch, dinner, and an evening snack, subjects were given free access to a main entree varying in energy density (low, medium, or high). The manipulated main entrees were similar in palatability to their counterparts across conditions. Low-energy compulsory (consumption required) side dishes accompanied each meal. Subjects also consumed a standard, compulsory breakfast. Results showed that subjects consumed a similar amount of food (by weight) across the three conditions of energy density. Thus, significantly more energy was consumed in the condition of high energy density (7532 +/- 363 kJ, or 1800 +/- 86 kcal) than in the medium- (6356 +/- 281 kJ, or 1519 +/- 67 kcal) and low- (5756 +/- 178 kJ, or 1376 +/- 43 kcal) energy-density conditions (P < 0.0001). There were no differences in hunger or fullness before meals, after meals, or over the 2 d across conditions. The results from this study indicate that energy density affects energy intake independent of macronutrient content or palatability, suggesting that the overconsumption of high-fat foods may be due to their high energy density rather than to their fat content.     

Hunger enhances the expression of calorie- but not taste-mediated conditioned flavor preferences.

Compared ethanol-mediated flavor preferences to preferences mediated by saccharin, which is sweet but noncaloric, and sucrose, which is both sweet and caloric in 4 experiments, using 74 Long-Evans rats. Ss learned to associate grape or orange flavor conditioned stimulus/stimuli (CS) with (1) ethanol or saccharin solution or (2) either the other unconditioned stimulus/stimuli (UCS) or plain tap water. They were then given 2-bottle choice tests between the flavor CSs apart from the UCSs. Flavors associated with 5% ethanol were preferred over saccharin-paired and water-paired flavors by sated Ss, and food deprivation during the choice test enhanced this preference. Flavors associated with 8% sucrose were preferred over water-paired flavors, and this preference was also enhanced by food deprivation. Flavors associated with 0.028% or 0.25% saccharin were preferred over flavors paired with water. In all cases, calorie-mediated preferences, at their highest levels, were stronger than taste-mediated preferences. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased liking for a solution is not necessary for the attenuation of neophobia in rats.

Recent evidence suggests that liking and wanting of food rewards can be experimentally dissociated (e.g., Berridge, 1996); this dissociation extends to attenuated neophobia in the present study. Rats tend to eat less of a novel food than a familiar food, a phenomenon called neophobia. The present experiments evaluated whether attenuation of neophobia by prior exposure reflects enhanced liking of the flavor using the Taste Reactivity (TR) test. In Experiment 1, rats given five 10-s TR trials with water or various concentrations of saccharin solution (0.1%, 0.2%, 0.5%) did not show a change in the number of hedonic reactions displayed across trials. However, in a subsequent consumption test from a bottle containing 0.25% saccharin solution, rats with no prior saccharin exposure (group water) consumed less than rats with prior saccharin exposure; that is they displayed neophobia. In Experiment 2, whether rats received five 10-s TR trials with water or 0.5% saccharin solution, they did not display a difference in hedonic reactions to 0.25% saccharin solution in two 5-min TR test trials. These results suggest that the attenuation of neophobia is evidenced as an increase in the tendency to approach a bottle containing the flavored solution (wanting), but not as an enhanced liking of that solution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bed rails: a barrier to independence?

The influence of meal frequency on change of body weight and protein status, measured by level of amino acid oxidation (decarboxylation) in the postabsorptive state, was studied at a fixed daily protein intake. Growing rats (250g) were fed through gastric canula a feeding solution based on Nutrison Standard supplying 1.6g protein and 266kJ ME daily. This amount was given in either 2 large meals at the beginning and the end, or in 6 smaller meals, or by continuous infusion during entire dark period (10 hrs). After 3 weeks of feeding the mean growth rate of the rats fed continuously was nearly 20% higher than rats fed the same amount in 2 meals. The rats fed 6 meals a day had a growth rate rather similar to the rats fed continuously. The percentile recovery of label as 14CO2 in the breath after an intraperitoneal injection of [1-14C]leucine (4 hrs after last meal) was significantly higher (p.05) for the animals fed continuously (27% sd 2.6) compared to the rats fed 2 meals (21.9% sd 4.0). The value for 6 meal group was intermediate (24.5 sd 1.8). The results indicate that the metabolic utilization of a fixed daily amount of protein is clearly influenced by the way of supply. With respect to the change of body weight and protein status, animals have more benefit of the same amount of protein if the supply is more equable. It is suggested that the difference is caused by metabolic restriction for an adequate utilisation of large meals. Therefore large meals are supposed to cause a waste of amino acids in the postprandial phase. As a consequence amino acid amount that will be stored in the body to be available in the postabsorptive phase will be less.     

Vigabatrin-induced lesions in the rat brain demonstrated by quantitative magnetic resonance imaging

Previous research has indicated that individual foods or beverages are ingested independently and do not produce adjustments to the intake of other constituents in the diet (de Castro, 1993; Wilson, 1991). In order to eliminate time of day as a potential contaminant, the present study investigated the accommodation of foods and beverages into the amount ingested at large evening meals only. Adults (n = 601) were paid to maintain detailed diaries of the timings, quantities and preparation techniques of everything they ingested for seven consecutive days. With the exceptions of soup, beef and chicken, 12 out of 15 types of drinks or foods were found to add to the total calories ingested in evening meals without displacing calories ingested in other forms, while ingestion of non-caloric diet sodas was not associated with differences in intake. The fat and protein, but not carbohydrate, contents of the items correlated with a measure of the satiating properties of the particular food or beverage, namely the correlation between the amount ingested of the particular type and the amounts of other nutrients ingested in the meal. The results confirm that intake at a meal is quite elastic and can be significantly influenced by the presence or absence of particular components of the meal and their constituents.     

Schedule-induced polydipsia: An artifact.

Conducted 6 experiments with 4 female rats in which they were allowed access to Noyes pellets for 1 hr/day with water freely available at all times. The food was presented either ad lib or in a lever-pressing situation on various interval schedules of reinforcement. The size of the individual reinforcements ("bites") was varied between experiments. Schedule-induced polydipsia was obtained when the S's meal consisted of a large number of very small bites. When the meal consisted of a smaller number of larger bites, polydipsia did not occur. The experiments collectively indicate that the amount of water consumed while eating is a function of the number of bites taken and independent of bite size or total food consumption. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of simultaneous oral–intragastric ingestion on meal patterns and satiety in humans.

Simultaneous oral–intragastric ingestion of a liquid diet was compared with oral ingestion for 15–21 days in 4 18–21 yr old males of normal weight. All the Ss ate significantly more during simultaneous compared with oral lunches and dinners. Ss reduced the size and frequency of breakfasts and snacks, which were always ingested orally, however, and did not gain weight. In a 2nd experiment, the same 4 Ss ate significantly more at lunch when the rate of ingestion was 200 cm–3/min compared with 100 cm–3/min regardless of route. They also ate significantly more during simultaneous meals compared with oral or intragastric meals ingested at the same rate. Thus, rate of ingestion and oral stimulation are important determinants of meal size in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of meal patterns of the rat.

Two experiments, one with 6 18-60 day old female Wistar rats and the other with 12 Wistar and Long-Evans rats, examined the development of adult rat meal patterns. Although diurnal differences in food intake were present as early as 18 days after birth, with significantly more food being consumed in the dark, these differences were much smaller than those seen in adults. Nocturnal feeding gradually increased, reaching adult levels at around 6 wks of age. In general, little or no direct correlation was observed between meal size and postmeal interval length until rats were 4-5 wks old. Thereafter, correlations of +.40 or higher were usually observed. On the other hand, correlations averaging around zero were observed between meal size and premeal interval at all ages studied. Results are discussed in terms of their implications for proposed physiological mechanisms determining meal onset. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of thermic effect of food on satiety

OBJECTIVES: To evaluate energy expenditure after three isoenergetic meals of different nutrient composition and to establish the relationship between the thermic effect of food (TEF), subsequent energy intake from a test meal and satiety sensations related to consumption. DESIGN: The study employed a repeated measures design. Ten subjects received, in a randomized order, three meals of 2331+/-36 kJ (557+/-9 kcal). About 68% of energy from protein in the high protein meal (HP), 69% from carbohydrate in the high carbohydrate meal (HC) and 70% from fat in the high fat meal (HF). SETTING: The experiments were performed at the University of Milan. Subjects: Ten normal body-weight healthy women. METHODS: Energy expenditure was measured by indirect calorimetric measurements, using an open-circuit ventilated-hood system; intake was assessed 7h later by weighing the food consumed from a test meal and satiety sensations were rated by means of a satiety rating questionnaire. RESULTS: TEF was 261+/-59, 92+/-67 and 97+/-71 kJ over 7 h after the HP, HC and HF meals, respectively. The HP meal was the most thermogenic (P < 0.001) and it determined the highest sensation of fullness (P=0.002). There were no differences in the sensations and thermic effect between fat and carbohydrate meals. A significant relationship linked TEF to fullness sensation (r=0.41, P=0.025). Energy intake from the test meal was comparable after HP, HC and HF meals. CONCLUSIONS: Our results suggest that TEF contributes to the satiating power of foods.     

The ability of the rat to metabolize myristoyl-methionine: an acylamino acid with potentially useful antibacterial properties

Two experiments with Sprague Dawley rats tested their ability to hydrolyse myristoyl-methionine (M-M) into myristic acid and L-methionine (M). In the first experiment, lasting for 3 days. male rats were orally administered [9,10-3H]myristoyl-L-[35S]methionine. The recovery of radioactivity was approximately 90% for both isotopes; 19% of the administered 3H was recovered in the urine and 16% in the faeces, while the recovered 35S activity was 13 and 12%, respectively. The balance of the radioactivity was found among the tissues, organs and blood. In the second experiment, male and female rats received soybean-based diets which were supplemented with either 0.305% M-M or 0.2% M (both diets contained equal amounts of M) for periods up to 4 weeks. The growth rate of the rats receiving the 0.305% M-M diets was slightly slower than that for the rats on the 0.2% M diet, but the difference was not statistically significant (P > 0.05). The M-M rats had a transitory decrease in feed consumption, suggesting that palatability may have contributed to the growth difference and that a somewhat greater amount of M-M was necessary for the rat to attain the same growth rate as that produced by 0.2% M. When the amount of dietary M-M was increased to 3.05% M-M, a greater reduction in feed consumption and body weight gain was observed. This latter diet was an initial attempt to study the potential toxicity of M-M. None of the haematological, clinical chemistry or organ weight data suggested that M-M was overtly toxic per se, but longer-term feeding studies are needed to evaluate the potential toxicity of M-M more fully.     

Abdominal vagotomy disrupts food-related drinking in the rat.

In 2 experiments with a total of 41 Sprague-Dawley albino rats, Ss with complete subdiaphragmatic bilateral transection of the abdominal vagus (Vgx-C) showed disordered food-related drinking when drinking water in temporal association with a meal of dry food after 5-hr food deprivation and when drinking water in association with a liquid meal after 24-hr food deprivation. The Vgx-C Ss drank after significantly longer latencies and drank significantly less water in 1 hr than did sham-vagotomized (Sham) Ss after eating the same size meal (solid or liquid). Ss with incomplete vagal transection (Vgx-I) ate and drank like Shams. Water intake of Sham and Vgx-I Ss correlated positively with the meal size of solid food, but the water intake of Vgx-C Ss did not. The failure of Vgx-C Ss to drink water normally when food was ingested was not due to failure of a food stimulus to reach the intestine, because Vgx-C and Sham Ss emptied equivalent volumes of liquid food from the stomach into the intestine within 10 min of food entering the stomach. Results indicate that the abdominal vagus is an important neurological substrate for food-related drinking in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)