The role of novelty and fat and sugar concentration in food selection by captive tufted capuchins (Sapajus apella)

Capuchins, like other primates, use feedback from sensory cues and digestion to make decisions about which foods to consume and which to avoid. However, little is known about how capuchins make consumption decisions when simultaneously presented with novel and familiar foods, or how food familiarity and macronutrient concentration together influence food choice, topics with potential implications for developmental and health research. In this study, we evaluated the role of familiarity, as well as fat and sugar concentration, in the food selections of captive tufted capuchins (Sapajus apella). In the first experiment, over 10 sessions, subjects were assigned to either a group that chose between one familiar and one novel food item both high in fat or sugar (high condition), or to a group that chose between one familiar and one novel food item both low in fat or sugar (low condition). In the second experiment, subjects were divided into three groups, familiarized with food over five feeding sessions, and then offered the familiarized food and a novel food that varied in fat or sugar for 10 sessions. When offered foods high in fat, capuchins showed no clear signs of neophobia, forming an initial preference for the novel food, rejecting foods less frequently, and selecting foods faster than when offered foods low in fat. These trends were generally not observed in response to foods with sugar. When presented with options that varied in macronutrient concentration, subjects showed an initial interest in the novel food irrespective of whether it was high in fat or sugar, yet formed a final preference for the higher-concentration item. Findings suggest that the concentration of fat or sugar in novel foods may be an important mediator of exploratory behavior and that capuchins rely on immediate feedback from taste and other sensory cues to make consumption decisions.     

Early weaning programs rats to have a dietary preference for fat and palatable foods in adulthood

The objective of this work was to study the effect of early weaning on alimentary preference for the macronutrients protein, carbohydrate and fat in adult rats. Male Wistar rat pups were weaned by separation from the mother at 15 (D15) or 30 (D30) days old. Body weight and food intake were measured every 30 days until pups were 150 days old. At 110 days of age, the alimentary preference was evaluated for 1 h on 3 consecutive days. At 120 days of age, the palatable diet test was conducted during 3 consecutive 24-h periods. Body weight and food intake were not altered, but early weaning in rats induced an alimentary preference to fat and hyperphagia of a palatable diet. In conclusion, early weaning, although did not modify body weight or basal food intake, promoted an increased preference for palatable and fatty foods. This demonstrates that early weaning is not capable of promoting perceptible alterations of alimentary behavior under normal laboratory conditions. However, in the presence of a stimulating factor such as a choice of nutrients or a palatable diet, a possible latent effect on dietary preferences may become apparent. Over the long term, this preference for foods with high caloric density can lead to obesity and metabolic perturbations.     

Feeding Response of Rats to No-Fat and High-Fat Cakes

The nutritional effects of high-fat diets have been extensively studied in laboratory animals, but as yet few experiments have examined the feeding response of animals to newly developed fat substitutes. The present study used commercially available no-fat (0% fat, 92% carbohydrate) and high-fat (41% fat, 54% carbohydrate) cake to determine the effects of fat substitutes on food preference and caloric intake in rats. The first experiment showed that nondeprived rats found the high-fat and no-fat cakes equally palatable and highly preferred to lab chow. Food deprived rats, however, preferred the high-fat cake to the no-fat cake, which may be related to its higher caloric density. In the second experiment, rats fed high-fat cake, in addition to chow, for 30 days consumed more calories and gained more weight than did rats fed no-fat cake and chow. The no-fat cake group, however, overate and gained more weight than chow-only controls. The hyperphagic response to the no-fat cake can be attributed to its carbohydrate content, moisture, and high palatability. Thus, removing fat from the cake reduced, but did not eliminate, its obesity-promoting effect. Obviously, low-fat foods must be consumed in moderation if used for weight control.     

Rhesus macaques (Macaca mulatta) are not neophobic toward novel food with a high sugar content

While we know that food neophobia in nonhuman primates is affected by social factors, little is known about how palatability, and specifically sugar content, might ameliorate a monkey's hesitancy to eat a novel food. It is likely that an innate preference for sweet substances would alter an animal's typical neophobic response. To test this, I presented nine male rhesus macaques with novel foods that contained a low, high, or no amount of sugar. As expected, the monkeys exhibited a neophobic response to the no-sugar novel foods but not to the high-sugar novel foods. Previous research on food neophobia may need to be reevaluated in light of the effects of sugar content on the neophobic response.     

Neuropeptide Y administration into the amygdala alters high fat food intake

The orexigenic effects of neuropeptide Y (NPY) are mediated through the hypothalamus, while the anxiolytic effects of NPY appear to be mediated through the amygdala. We hypothesized that intra-amygdalar administration of NPY might alter food preference without changing total food intake. Neuropeptide Y was administered into the central nucleus of the amygdala in both satiated and overnight-fasted rats, and intake and preference for a high fat diet (56%)/low carbohydrate (20%) diet or a low fat (10%)/high carbohydrate (66%) diet were measured. Intra-amygdalar NPY administration in satiated rats did not change total caloric intake, but it did produce a dose-dependent decrease in intake of and preference for high fat diet relative to low fat diet over 24 h. In overnight-fasted rats, intra-amygdalar NPY also decreased the intake and preference for a high fat diet relative to low fat diet over 24 h, without altering total caloric intake. Intra-amygdalar NPY administration did not produce conditioned taste aversions to a novel saccharin solution. These results suggest that amygdalar NPY may have a role in macronutrient selection, without altering total caloric intake.     

A trial of assessment of the interrelated action of metabolic and sensory factors in the choice of food by rats in various states of protein and calcium nutrition

The strategy of food choice by adult rats was studied after giving previously to them a balanced diet, a non-protein diet and/or a diet with calcium excess. Tests were carried out for food preference offering to the rats semi-purified diets differing in the contents of protein and calcium. Besides that, the taste of the food was changed adding to it saccharose, quinine, mint and caramel. Depending on the nutritional state of the rats significant differences were found in their preference for foods which was related to the general direction of homeostasis recovery. In protein malnutrition diets were chosen containing protein, while calcium content and taste were of secondary importance.     

Ghrelin enhances cue-induced bar pressing for high fat food

Ghrelin is an orexigenic hormone produced by the stomach that acts on growth hormone secretagogue receptors (GHSRs) both peripherally and centrally. The presence of GHSRs in the ventral tegmental area (VTA) suggests that ghrelin signaling at this level may increase the incentive value of palatable foods as well as other natural and artificial rewards. The present investigation sought to determine if ghrelin plays a role in relapse to such foods following a period of abstinence. To achieve this, thirty-six male Long Evans rats were trained to press a lever to obtain a high fat chocolate food reward on a fixed ratio schedule of 1. Following an extinction period during which lever presses were not reinforced, rats were implanted with a cannula connected to a minipump that continuously delivered ghrelin, a GHSR antagonist ([d-Lys-3]-GHRP-6), or saline in the VTA for 14 days. One week later, food reward-associated cues, food reward priming, and an overnight fast were used to induce reinstatement of the lever pressing response. Our results indicate that intra-VTA ghrelin enhances cue-induced reinstatement of responses for palatable food pellets. To the extent that the reinstatement paradigm is considered a valid model of relapse in humans, this suggests that ghrelin signaling facilitates relapse to preferred foods in response to food cues through GHSR signaling in the VTA.     

Bottle-choice tests in Sprague-Dawley rats using liquid diets that differ in oil and sucrose contents

Bottle choice tests using liquid diets were done with Sprague-Dawley (SD) rats. SD rats ingested more oil-and-sucrose-enriched milk (hi-fat) and less oil-enriched milk (hi-fat-no-carb) than sucrose-enriched (hi-carb) milk by two-bottle choice tests after they were habituated to liquid diets for 4 days. Chronic food restriction didn't increase hi-fat ingestion but hi-fat-no-carb. Rats ingested less without habituation, and overnight food deprivation increased intake. This increment was maintained after rats were free-fed. The difference in fat content of the maintenance diet had little effect on fat preference. These results showed SD rats prefer a sweet and fatty liquid diet than a sweet and lean liquid diet. Habituation and food restriction were more important than the composition of the maintenance diet to demonstrate a clear preference for the fatty liquid diet.     

Increased expression of mu opioid receptors in animals susceptible to diet-induced obesity

Stimulation of mu opioid receptors preferentially increases the intake of a high fat diet. In this paper we investigated whether there was a difference in the expression of mu opioid receptors between animals susceptible (Osborne–Mendel) or resistant (S5B/Pl) to obesity induced by eating a high fat diet. Immunohistochemical studies demonstrated that Osborne–Mendel rats eating a chow diet had an increased number of mu opioid receptors in the arcuate nucleus when compared to S5B/Pl rats. These immunohistochemical findings were supported by Real Time-PCR which demonstrated that the mRNA level of mu opioid receptors was also increased in the hypothalamus of Osborne–Mendel rats compared to S5B/Pl rats. Low doses of the mu opioid receptor agonist DAMGO [d-Ala²-N-Me-Phe⁴-Glycol⁵]-enkephalin administered to Osborne–Mendel rats caused a significant increase in the preference for a diet high in fat. The same doses of DAMGO switched the diet preference of S5B/Pl rats to high fat but did not significantly increase food intake. The combination of these findings suggests that the increased levels of hypothalamic mu opioid receptors in Osborne–Mendel rats may contribute to their preference for a diet high in fat and increase their susceptibility to becoming obese.     

Social exploitation of intermittently available foods and the social reinstatement of food preference

To determine whether Norway rats, Rattus norvegicus, could use socially acquired information to track recurrences of an intermittently available food (experiment 1), we allowed observer rats to interact every 2-3 days with demonstrator rats fed one of two diets, then determined the amount of each diet eaten by observers. We found that observer rats showed repeated significant increases in their preferences for foods their respective demonstrators had eaten. Because social interactions repeatedly enhanced preference for a food, we reasoned that after the socially induced food preference of an animal (A1) had waned, that preference might be reinstated in A1 by interaction with a conspecific (A2) in whom A1 had previously induced a preference for the food. In experiment 2, we demonstrated such social reinstatement of a food preference. Copyright 2000 The Association for the Study of Animal Behaviour.     

Diet selection by red-backed voles<Emphasis Type="Italic">Clethrionomys gapperi</Emphasis>

Food supplementation studies often assume that animals will select artificial diets in their natural environment, and that high-protein, high-energy foods are the most appropriate supplement. These assumptions were tested in red-backed volesClethrionomys gapperi Vigors, 1830 using food-choice experiments with sunflower seeds, oats, and commercial diets in the laboratory and field. Preferred level of dietary protein was also examined using isocaloric diets that varied only in protein content (14%, 20% and 30%). Preferences exhibited in the above trials were subsequently examined relative to natural forage. Voles demonstrated a strong preference for sunflower seeds over oats, dried alfalfa, and rabbit, guinea pig, rat and cat food. Voles preferred the 14% protein diet over the 20% and 30% protein diets. Although sunflower seeds contain more than 20% protein, voles consistently preferred this food over natural forage, perhaps because of their high fat and energy content. This indicates that tradeoffs in protein content may be made to maximize energy. We suggest that red-backed voles will select sunflower seeds in their natural environment, and that their preference for low protein likely reflects their herbivorous diet. This study highlights the importance of ana priori understanding of species-specific preferences and requirements when designing food supplementation studies.     

Stress induced differential intake of various diets and water by rat: the role of the opiate system

The purpose of this study was to explore the effect of acute mild stress (12–48 hour food and water deprivation) and acute severe stress (12 hour food and water deprivation followed by 10 min swim in water at 4°) on the intake of different isocaloric dietary regimes. Each group of experimental animals was given only one particular diet. Rats subjected to mild stress showed very little preference of dietary regimes. When the food intake was measured during 3 hour period, following 48 hours of fasting, animals showed 2 to 3 fold increase in the food and water intake but no particular dietary preference. However, when rats were subjected to severe stress, there was an increase in the food intake of 154% (control diet); 174% (high-carbohydrate diet); 310% (high protein diet) and 423% (high fat diet) compared to animals subjected to mild stress. In terms of the absolute quantity of food, the animals subjected to severe stress ate more high-fat diet than any other diet; the consumption of high fat diet was 142% more than high-protein diet, 180% more than control diet and 258% more than high carbohydrate diet. Animals subjected to severe stress and given high-carbohydrate and high fat diet also showed 80% increase in the water intake. Prior administration of naloxone (1 mg/kg body weight, i.p.) reduced the stress induced increase in the intake of food and water. Naloxone inhibited the intake of high-fat diet more than any other diet. The ability of naloxone to block the increase in the intake of high-fat diet, and the reported increase in the concentration of β-endorphin in the different regions of brain of the animals subjected to the cold swim, suggest that endogenous opioid system in body is activated during stress. An activation of the endogenous opioid system leads to a preferential increase in the intake of palatable foods.     

Food Deprivation Increases the Rat's Preference for a Fatty Flavor Over a Sweet Taste

Previous research indicates that food deprivation increasesthe rat's preference for high-fat over low-fat foods. Sincethese foods differ in their flavors and post-ingestive effects,both factors may be implicated. The present study investigatedpreferences in food deprived and non-deprived rats using non-nutritivemineral oil emulsion (MO) and saccharin solution (SAC), whichhave a fatty flavor and sweet taste, respectively. The deprivedrats consumed more MO than SAC in one- and two-bottle tests,while the non-deprived rats ingested as much SAC as MO in one-bottletests and preferred SAC in two-bottle tests. Several aspectsof the data suggest that the deprivation-related shift in preferencebetween MO and SAC was determined by changes in long-term energybalance. A follow-up conditioning experiment discarded the possibilitythat the observed preference shift was related to differentialreinforcing effects of the two substances. In conclusion, long-termfood restriction increases the preference for an oily flavorover a sweet taste via a mechanism that does not involve nutritivefeedback. It remains to be determined to what extent this alterationin flavor preference influences food selection when post-ingestivenutritive feedback can influence food choice. Chem. Senses 21:169–179, 1996.     

Avoidance of potentially harmful food cannot be socially transmitted between rats

The social transmission of food preferences(STFP) is a behavioural task of olfactory memory, in which an observer rat learns safe food odours from a demonstrator rat, and shows preference for this odour in a subsequent choice test. However, previous studies have failed to detect the transmission of information about food of potential danger and food aversion using STFP test. In this study, we tested how demonstrators' health affects the exchange of odour information and whether observers can learn danger information from an unhealthy demonstrator. As expected, the observer rat formed an odour preference after interacting with a demonstrator rat that had just eaten food containing a new odour, however, odour preference rather than aversion was also formed after interacting with a demonstrator rat injected with LiCl(used to induce gastric malaise). Furthermore, anaesthetized demonstrator rats and half-anaesthetized demonstrator rats, which showed obvious motor deficits suggesting an unhealthy state, also socially transmitted food preferences to observers. These results suggest that the social transmission of food preferences task is independent of a demonstrators' health, and that information about dangerous foods cannot be transmitted using this behavioural task.     

Olanzapine effects on body composition, food preference, glucose metabolism and insulin sensitivity in the rat

The atypical antipsychotic drug olanzapine induces weight gain and defects in glucose metabolism in patients. Using a rat model we investigated the effects of acute and long term olanzapine treatment on weight gain, food preference and glucose metabolism. Olanzapine treated rats fed a chow diet grew more slowly than vehicle controls but olanzapine treated animals fed a high fat/sugar diet grew faster than control animals on the same diet. These changes in weight were paralleled by changes in fat mass. Olanzapine also induced a strong preference for a high fat/high sugar diet. Acute exposure to olanzapine rapidly induced severe impairments of glucose tolerance and increased insulin secretion but did not impair insulin tolerance. These results indicate the defect in glucose metabolism induced by acute olanzapine treatment was most likely due to increased hepatic glucose output associated with a reduction in active GLP-1 levels and correspondingly high glucagon levels.     

Phleichrome; A New Phytotoxic Compound Produced by Cladosporium phlei

Bottle choice tests using liquid diets were done with Sprague-Dawley (SD) rats. SD rats ingested more oil-and-sucrose-enriched milk (hi-fat) and less oil-enriched milk (hi-fat-no-carb) than sucrose-enriched (hi-carb) milk by two-bottle choice tests after they were habituated to liquid diets for 4 days. Chronic food restriction didn't increase hi-fat ingestion but hi-fat-no-carb. Rats ingested less without habituation, and overnight food deprivation increased intake. This increment was maintained after rats were free-fed. The difference in fat content of the maintenance diet had little effect on fat preference. These results showed SD rats prefer a sweet and fatty liquid diet than a sweet and lean liquid diet. Habituation and food restriction were more important than the composition of the maintenance diet to demonstrate a clear preference for the fatty liquid diet.     

Dietary fat increases energy intake across the range of typical consumption in the United States

Objective: The fat content of a diet has been shown to affect total energy intake, but controlled feeding trials have only compared very high (40% of total calories) fat diets with very low (20% of total calories) fat diets. This study was designed to measure accurately the voluntary food and energy intake over a range of typical intake for dietary fat. Methods and Procedures: Twenty‐two non‐obese subjects were studied for 4 days on each of three diets, which included core foods designed to contain 26, 34, and 40% fat, respectively of total calories and ad lib buffet foods of similar fat content. All diets were matched for determinants of energy density except dietary fat. Subjects consumed two meals/day in an inpatient unit and were provided the third meal and snack foods while on each diet. All food provided and not eaten was measured by research staff. Results: Voluntary energy intake increased significantly as dietary fat content increased (P = 0.008). On the 26% dietary fat treatment, subjects consumed 23.8% dietary fat (core and ad lib foods combined) and 2,748 ± 741 kcal/day (mean ± s.d.); at 34% dietary fat, subjects consumed 32.7% fat and 2,983 ± 886 kcal/day; and at 40% dietary fat subjects consumed 38.1% fat and 3,018 ± 963 kcal/day. Discussion: These results show that energy intake increases as dietary fat content increases across the usual range of dietary fat consumed in the United States. Even small reductions in dietary fat could help in lowering total energy intake and reducing weight gain in the population.     

Serotonin,Eating Behavior,and Fat Intake

There is an intimate relationship between nutritional intake (eating) and serotonin activity. Experimental manipulations (mainly neuropharmacological) of serotonin influence the pattern of eating behavior, subjective feelings of appetite motivation, and the response to nutritional challenges. Similarly, nutritional manipulations (food restriction, dieting, or altered nutrient supply) change the sensitivity of the serotonin network. Traditionally, serotonin has been linked to the macronutrient carbohydrate via the intermediary step of plasma amino acid ratios. However, it has also been demonstrated that 5-HT drugs will reduce energy intake and reverse body weight gain in rats exposed to weight increasing high fat diets. 5-HT drugs can also reduce food intake and block weight gain of rats on a high fat cafeteria diet. Some diet selection studies in rats indicate that the most prominent reduction of macronutrient intake is for fat. These data indicate that 5-HT activity can bring about a reduction in fat consumption. In turn, different types of dietary fat can alter brain 5-HT activity. In human studies the methodology of food choice experiments has often precluded the detection of an effect of 5-HT manipulation on fat intake. However, there is evidence that in obese and lean subjects some 5-HT drugs can readily reduce the intake of high fat foods. Data also suggest that 5-HT activation can lead to a selective avoidance of fat in the diet. These effects of 5-HT on the intake of dietary fat may involve a pre-absorptive mechanism and there is evidence that 5-HT is linked to cholecystokinin and enterostatin. These proposals have theoretical and practical implications and suggest possible strategies to intensify or advance fat-induced satiety signals.     

Great apes prefer cooked food

The cooking hypothesis proposes that a diet of cooked food was responsible for diverse morphological and behavioral changes in human evolution. However, it does not predict whether a preference for cooked food evolved before or after the control of fire. This question is important because the greater the preference shown by a raw-food-eating hominid for the properties present in cooked food, the more easily cooking should have been adopted following the control of fire. Here we use great apes to model food preferences by Paleolithic hominids. We conducted preference tests with various plant and animal foods to determine whether great apes prefer food items raw or cooked. We found that several populations of captive apes tended to prefer their food cooked, though with important exceptions. These results suggest that Paleolithic hominids would likewise have spontaneously preferred cooked food to raw, exapting a pre-existing preference for high-quality, easily chewed foods onto these cooked items. The results, therefore, challenge the hypothesis that the control of fire preceded cooking by a significant period.     

Protein appetite is increased after central leptin-induced fat depletion

Leptin reduces body fat selectively, sparing body protein. Accordingly, during chronic leptin administration, food intake is suppressed, and body weight is reduced until body fat is depleted. Body weight then stabilizes at this fat-depleted nadir, while food intake returns to normal caloric levels, presumably in defense of energy and nutritional homeostasis. This model of leptin treatment offers the opportunity to examine controls of food intake that are independent of leptin's actions, and provides a window for examining the nature of feeding controls in a "fatless" animal. Here we evaluate macronutrient selection during this fat-depleted phase of leptin treatment. Adult, male Sprague-Dawley rats were maintained on standard pelleted rodent chow and given daily lateral ventricular injections of leptin or vehicle solution until body weight reached the nadir point and food intake returned to normal levels. Injections were then continued for 8 days, during which rats self-selected their daily diet from separate sources of carbohydrate, protein, and fat. Macronutrient choice differed profoundly in leptin and control rats. Leptin rats exhibited a dramatic increase in protein intake, whereas controls exhibited a strong carbohydrate preference. Fat intake did not differ between groups at any time during the 8-day test. Despite these dramatic differences in macronutrient selection, total daily caloric intake did not differ between groups except on day 2. Thus controls of food intake related to ongoing metabolic and nutritional requirements may supersede the negative feedback signals related to body fat stores.