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The contribution of taste to the food choices of foraging rats was examined. Rats in a laboratory foraging paradigm searched for sequential opportunities to eat at two feeders containing chow-based food pellets that were plain or flavored with saccharin or citric acid. Pellets cost the same number of bar presses at both feeders. Saccharin adulteration had no effect on intake parameters. Citric-acid-flavored pellets were eaten more slowly and in smaller meals. If there was no alternative food, daily intake was slightly reduced. When the alternative food was plain, fewer meals and fewer pellets were taken of the citric-acid-flavored than plain pellets. When we gradually increased the price of the plain pellets at one feeder, while the price at the alternative feeder (which contained either plain or citric-acid-flavored pellets) remained low, the rate of eating (profitability) decreased at the higher-price feeder, and the rats shifted their intake toward the less-costly, more profitable pellets. We compared the relationship between the relative eating rate at each feeder and the relative meal size (or daily intake) at each feeder when the low-priced food was plain and when it was flavored with citric acid, and found no differences. This indicates that taste may influence choice via its effect on rate of intake.

The avid consumption of pure carbohydrate solutions, which often results in a distortion of nutrient balance, is generally presumed to be driven by their taste. In the first of two experiments, we examined the effect of consumption cost on rats' intake of three concentrations of sucrose solution (8%, 16%, and 32%) when a nutritionally complete chow was concurrently freely available. In the second experiment, we examined the intake of 24% sucrose solution and chow as the consumption costs of both were varied. Increasing the cost of sucrose resulted in a reduction in the percent calories taken from sucrose; the steepness of the decline in intake with price was inversely related to the sucrose concentration and to the cost of chow. Chow calories were substituted for relatively expensive sucrose calories. An increase in the cost of chow resulted in a reduction in the percent of calories taken from chow and a protein-poor diet. The cost of sucrose did not affect the slope of the chow intake curve, presumably because, despite its sweet taste, sucrose was not a substitute for the protein, fat, and micronutrients in chow. Total caloric intake was conserved in all cases.Thus, the avid consumption of sucrose solution is curtailed when it is costly; but the degree of change in intake with cost depends on the cost of an alternative food. These results suggest that diet selection involves a comparison not only of the taste and post-ingestive consequences of available foods, but also of the cost of calories and nutrients in the foods. Selection appears to be guided first by caloric requirements and the relative cost of calories, then by nutrient requirements and the relative cost of nutrients, and finally by taste.

The aim of this study was to assess the dietary practices of 10 elite female surfers. Four- and five-day food diaries completed over competition and training periods demonstrated energy intakes (mean +/- SD) of 9,468 kJ (+/- 2,007) and 8,397 kJ (+/- 1,831), respectively. This level of energy intake was less than that estimated for the requirements of surfing. Female surfers' carbohydrate intakes failed to meet the recommendations, and suboptimal zinc intake was observed with 90% of subjects not meeting the Australian RDI. Comparisons between competition and training demonstrated that carbohydrate (g and g/kg body weight) and confectionary (g) intakes were significantly higher (p < .05) and protein intake was significantly lower (p < .05) during competition. These results show that although body fat stores were not compromised (mean 22%), self-reported energy, carbohydrate, and nutrient intakes were marginal in elite female surfers. Questionnaires revealed that 90% of surfers did not have good nutritional habits while traveling, which was compounded by a lack of knowledge of nutritional practices.

The ability of prehomeothermic chicks to thermoregulate behaviorally was studied in chicks with continuous access to heated nests, running wheels, and separate sources of high and low protein. In Experiment 1, cold-reared groups with heated or unheated transparent nests ate the same amount and selected the same dietary fractions, but chicks with heated nests ran less and grew faster. Despite this, groups maintained normal body temperatures. In Experiment 2, chicks were cold- or warm-reared with heated or unheated painted nests, or no nests. Cold-reared chicks with heated nests spent most of their time in them. They selected diets containing a higher protein:carbohydrate ratio than cold-reared chicks with unheated nests but ate less, thereby consuming less absolute protein and growing more slowly. Despite differences in growth, intake, and dietary choice, all chicks maintained normal body temperatures. These data reveal that behavioral thermoregulation has a privileged status for chicks over the first 3 weeks of life. Prehomeothermic chicks exercise complex and effective solutions to energetic challenges when offered behavioral options that simulate those available in nature.

Seven experiments with 324 chicks tested their ability to select a nutritionally adequate diet from separate sources of purified casein and various supplements, including gelatin (a source of two amino acids), a gelatin-creatine mixture (a source of three amino acids), and fiber (nonnutritive bulk). Nonselecting controls consumed the basal purified-casein diet or a supplemented purified-casein diet. Chicks in all selection conditions composed diets that yielded normal intake, normal body temperature, normal activity, and the maximum growth possible for their intake. They also selected components in the same percentages as in premixed diets. In all instances, their selection was nonrandom and regulated. What chicks included in their diet depended on what else was available. Although the specific percentage taken from each dietary component varied across different selection alternatives, these differences affected neither intake nor growth. Selection, per se, incurred a caloric cost. Chicks selecting from fractions of a corn-and-soy diet offset this cost by increasing intake compensatorily, but chicks with a purified-casein fraction did not, suggesting that some unspecified property of casein placed a ceiling on its intake. These findings unequivocally demonstrate that immature chicks not only can self-select nutritionally adequate diets, but can do so with unexpected precision by exploiting different but equally successful strategies.

Rats in a laboratory foraging simulation searched for sequential opportunities to feed in two patches that differed in the rate at which food pellets were delivered (controlled by fixed-interval schedules) and in the size of the pellets. The profitability of feeding in each patch was calculated in terms of time (grams per minute) and in terms of effort (grams per bar press). These values were the result of the imposed fixed interval, the size of the pellets, and the rate at which the rats pressed the bar in each condition. The rats ate more food and larger meals, but not more frequent meals, at the patch offering the higher rate of food consumption, calculated as grams per minute. The relative intake at any patch was a function of the relative rate of intake during meals at that patch compared to the other patch. Rats respond to explicit manipulations of feeding time in the same manner as they respond to manipulations of feeding effort.

Growing chicks offered diets containing either surfeit or inadequate protein in the day but adequate protein at night adopted a pattern of nocturnal feeding but did not eliminate diurnal meals. Their weight gain surpassed that of corresponding dietary controls who received continuous access to surfeit or inadequate protein but was less than that of chicks with continuous access to a standard diet. Chicks receiving the standard diet at night with no food available in the light phase also grew but did so at a slower rate than the diurnally feeding control group. The shift in feeding patterns was not accompanied by a shift in body temperature, nor was nocturnal antipredator behavior, characterized by sustained motoric inhibition, disrupted by nocturnal feeding. These data demonstrate that feeding specializations which have been selected over a species' evolutionary history are not rigidly fixed but can be modified by the economic relations in the current habitat.

In Experiment 1, the measurement of 24-hour food intake in two rats showed that treatment with dexamethasone-21-acetate (DEX) (0.5 mg/kg IP) produced a decrease in body weight which was at least partially due to a decrease in food intake (both meal frequency and meal size). In Experiment 2, the daily intake of three macronutrient sources was measured. These data showed that treatment with DEX (0.5 and 1.0 mg/kg IP) led to an acute increase in protein intake, a sustained decrease in fat intake and no change in carbohydrate consumption. We suggest that this change in macronutrient selection may be an adaptive response which serves to ameliorate some of the effects of DEX treatment.

Growth and intake of weanling rats on five casein-based purified diets and matched cereal-based diets were compared. The results support Lát's conjecture that the failure of animals to exhibit normal growth on some purified diets may be attributed to their failure to consume sufficient casein. Given a choice, the rats consumed both types of food, composing a diet in which the ratio of purified to cereal-based diet was 2:1, and they grew normally. Although the growth-promoting characteristics of caseins from different sources varied, the preference ratio between casein- and cereal-based diets was the same with one exception: a reduced preference for purified diet was shown by animals who had previously experienced subnormal growth for an extended period of time on a purified diet. These results show that all caseins are not equivalent in their growth-promoting properties. Further, they show that rats are exquisitely sensitive to the nutritional properties of their diets and, given the opportunity, can compose a diet which yields normal growth.

Investigations of palatability have often been confounded by nutritional, pharmacological or methodological problems. The present experiment examined the free-feeding meal patterns of two differentially preferred yet nutritionally equivalent diets. When the two diets were offered sequentially (Experiment 1), no differences were found in meal frequency, meal size, or meal duration. However, when the diets were offered simultaneously in Experiment 2, the preferred diet was consumed more frequently, in larger meals, and at a faster feeding rate than the less preferred diet. Further, the meal patterns in Experiment 2 of the preferred diet were identical with those found for both diets in Experiment 1. Therefore, the meal patterns of two diets with differing palatability depend upon the method of presentation with differences appearing when the diets are offered simultaneously but not when they are offered sequentially.

It has been hypothesized that the serotonergic system is involved in the regulation of carbohydrate and/or protein intake. Tests of this hypothesis using added dietary tryptophan and diets varying in the ratio of carbohydrate/protein resulted in depressed intakes of high carbohydrate/low protein diets, elevated intakes of low carbohydrate/high protein diets, and a reduction of total caloric intake. The present studies gave rats increased options for adjusting to added tryptophan by providing them with separate sources of protein, carbohydrate, and fat. The results showed the expected decrease in carbohydrate intake, but also increases in fat intake and, to a lesser extent, protein intake. Total caloric intake was conserved. Hypothalamic concentrations of serotonin and 5-hydroxyindole acetic acid indicated increased activity of the serotonergic system. These results lend support to serotonin's involvement in nutrient selection, in that carbohydrate consumption decreased in response to tryptophan loading, but indicate that other nutrients may also be affected. Given the option of altering fat intake, the animals maintained a constant caloric intake despite the reduction of carbohydrate consumption.

Adult female lean and obese Zucker rats were allowed to compose their own diets by giving them access to three macronutrient sources. After a baseline period, the fat source was serially diluted. In all, eight concentrations of fat were used. Dilution of the fat source promoted significant increases in the intake of fat by both lean and obese rats. The increased intake of fat was not simply compensatory in nature, but rather represented significant increases in fat consumption. These results suggest that the reported increased appetite for fat of the obese rat is not a unique trait of that genotype. Further, results from this experiment demonstrate that caloric and protein regulation mechanisms may not be controlling the intake of obese and lean rats as precisely as once believed.

Rats in a laboratory foraging paradigm had 24-hr-per-day access to a feeder where they could search, by completing a fixed number of bar presses, for an opportunity to eat one of a pair of foods differing in caloric density (2.5, 3, 3.5, or 4 kcal/g) and, in Experiment 2, the price of food pellets (10 to 50 bar presses per pellet). The rats could either accept the opportunity, and eat a meal, or reject it in favor of further search. Daily caloric intake was relatively constant. The rats always included both foods in their diet, but, for any particular food, the degree of inclusion in the diet and of acceptance of meal opportunities, the meal size, and the rate of eating were all functions not only of the price and caloric value of that food but also of the price and value of the alternately-available food. The patterns of intake for one food relative to those for the other available food were strongly correlated with the relative rate of calorie intake during consumption of that food compared to the other. Although the rats appeared to be sensitive to the local rates of calorie flow, they did not maximize daily calories consumed per time spent feeding.