Circadian patterns of drinking and eating in pygmy goats.

The eating and drinking patterns of pygmy goats fed ad lib and kept on a 12 h light/12 h dark cycle were recorded and analyzed. Eighty-four percent of drafts (drinking bouts) were associated with meals (feeding bouts). Only 42% of meals were associated with drafts. In the light phase meals associated with drafts were significantly larger than meals not associated with drafts, suggesting that meal size is increased by water intake around meals. Cumulative food intake was positively correlated with cumulative water intake, but the correlation was weaker during the dark phase than during the light phase. The results demonstrate that water intake in ruminants is associated with food intake, but the link between water and food intake seems to be more pronounced during the light phase than during the dark phase.     

Some determinants of intake and patterns of feeding in the guinea pig

Regulation of food and water intake was studied in young and adult Guinea pigs by continuously monitoring ad lib feeding and drinking patterns and by examining the response to levels of celluflour dilution that ranged from 20–75%. Meal size and the duration of the intermeal interval were not systematically related to the sizes of preceding meals or interval lengths. Variations in food intake were mediated almost entirely by changes in meal size. This parameter increased during growth, was elevated in the first meal following food deprivation, decreased when water was withheld and increased when water was returned. The probability of drinking within 20 min of eating was 0.80. Celluflour dilution led to a decrease in apparent caloric intake without a proportional decrease in body weight. Regulation of energy balance and meal to meal control of feeding in this monogastric, herbivorous rodent is discussed in relation to the Guinea pig's digestive physiology and ecological niche.     

The meal pattern of rats shifts from postprandial regulation to preprandial regulation when only five meals per day are scheduled

In order to investigate whether an observed difference in the meal patterns of rats and human may be due to constraints that humans have on the timing of meals and their large but infrequent meal pattern, rats had similar constraints imposed on their meal intake. Fifteen male Long-Evans rats were monitored in five individual enclosed chambers equipped with pellet sensing eatometers for three fourteen-day data collection periods. Both groups were monitored in a baseline ad lib condition, then one group (n = 7) was allowed access to food only once every two hours, while the second group (n = 8) was allowed to access only five times per day. Both groups were then monitored for a second ad lib baseline period. The imposition of both schedules reduced meal frequencies and estimated premeal stomach contents, and increased meal sizes and estimated postmeal stomach contents. The imposition of the five meal per day, but not the twelve meal per day schedule of meal access, eliminated the significant relationships between meal size and the postmeal interval evident during baseline conditions and produced significant relationships between meal size and the premeal interval and estimated premeal stomach content, not seen during baseline conditions. The rats under the five meal per day access schedule showed a preprandial pattern of intake very similar to that previously observed in humans eating ad lib. It was concluded that the preprandial pattern, typical of humans, is characteristic of intake involving large infrequent meals which produce stomach filling to an upper limiting threshold. The postprandial pattern, typical of rats, is characteristic of intake involving small frequent meals that are initiated when the stomach empties to a lower threshold. A peripheral, stomach capacity, model then, can be used to explain both the preprandial and the postprandial patterns. Which pattern is used depends upon environmental conditions.     

Role of hypothalamic norepinephrine in control of meal patterns

Feeding behavior has been shown to be strongly affected by central administration of catecholamines. In this study, we examined in freely-feeding rats the effect of hypothalamic norepinephrine (NE) injections on the basic parameters of spontaneous ingestion. Precise changes in feeding behavior in rats maintained on ad lib food and water intake were monitored by a PDP 8 computer connected to an apparatus capable of measuring licks and bites of food. Injections of NE were administered into the hypothalamic paraventricular nucleus, the most sensitive brain area for the elicitation of feeding through direct alpha-noradrenergic stimulation. In tests conducted under both light and dark conditions, NE facilitated food intake, primarily by an increase in meal size rather than meal frequency. The first meal after injection was increased in size and duration; the rate of eating was also enhanced. Whereas the following intermeal interval was significantly larger, subsequent meals and intermeal intervals appeared generally unaffected. This evidence is consistent with the proposal of a role for hypothalamic NE in the maintenance, rather than initiation, of feeding behavior in freely-feeding rats.     

Electroconvulsive shock and water deprivation: Effects on drinking behavior and locomotor activity in rats

The effects of electroconvulsive shock (ECS) were examined in 72 hooded rats maintained on either ad lib food and water or 23.75-hr water-deprivation (ad lib food) schedules. Although ECS significantly decreased water intake in an ad lib group during drinking-box testing sessions, water deprivation abolished the effect, as indicated by water intake, and drinking frequency and time. However, ECS significantly decreased the locomotor activity of an ad lib group during drinking-box testing; the deficit was also evident in a deprived group which received ECS. The implications of the findings for ECS studies which have used one-trial water-reinforced learning tasks were discussed.     

Food and water intake and weight regulation in the pigeon

The interaction of eating and drinking and the relation between intake and body weight was examined in pigeons maintained under laboratory conditions in order to obtain normative data on intake and weight regulation in this species. Under ad lib conditions food and water intake values are correlated, while deprivation of either nutrient leads to a reduction in the intake of the other. A linear relation between the log food intake and the log body weight was found under both ad lib and deprivation conditions. Following a period of food deprivation the pigeon shows both a short-term and a long-term compensatory increase in food intake whose magnitude is directly proportional to the degree of body weight loss produced by deprivation. The findings for the pigeon are similar in many respects to those reported for the rat and are discussed in relation to weight regulation and motivational mechanisms in hunger and thirst.     

Meal patterns of normal, untreated bulimia nervosa and recovered bulimic women

In order to examine the meal pattern characteristics associated with bulimia nervosa the meal patterns of 19 untreated bulimia nervosa, 12 recovered bulimics, and 21 normal controls spontaneously eating in their natural environments were compared. Subjects reported in a diary everything they either ate or drank for seven consecutive days. Meal pattern correlations included comparisons of the groups in regard to meal size (and binge size), meal frequency, premeal and postmeal intervals, deprivation ratios, satiety ratios, stomach contents, and composition of meals and binges. Results indicated that, although total reported intake was normal, only 33% of the total calories consumed by the untreated bulimia nervosa subjects were not followed immediately by purging. Both purged and unpurged binges were twice as large as their meal sizes which did not differ from normal. It is hypothesized that the caloric restriction of the untreated bulimics is binge/purge specific, and is used by them as a form of weight control. The recovered group showed a lack of responsivity to the signals that influence meal size and intermeal intervals in normals including impaired social facilitation of eating. They also had larger meal sizes, and greater frequency of meals. It is theorized that recovered bulimics employ other, as yet unspecified, means of food intake restriction resulting in an abnormal feeding pattern.     

Estrogen modification of feeding behavior in the female rat: influence of metabolic state

The effects of estrogen on feeding behavior and body weight regulation of adult ovariectomized rats were observed after 48 hr of food deprivation. The depletion of body nutrient stores caused by food deprivation resulted in an attenuation of the effects of estrogen treatment on food intake, eating time, meal size, meal duration and the number of meals. Nevertheless, estrogen treatment in fasted animals did shorten the interval between meals immediately after access to food was restored. Indices of the satiating effects of individual meals and the deprivation effects of intervals between meals were calculated for selected times. These indices also indicated an influence of estrogen even in the fasted condition. Estrogen diminished the satiety produced by the first meal after food access was restored, while the deprivation effects of the interval between the first and second meals were enhanced. During the dark period on the first day of refeeding, the satiating effects of food remained reduced in the fasted condition, and estrogen did not appear to further affect satiety compared to oil treatment, but estrogen did lower the deprivation effects of intermeal intervals compared to oil treatment. Estrogen treatment in non-fasted animals lowered both satiety and deprivation effects during the dark period. The varying influence of estrogen on the deprivation effects of intermeal intervals suggests that the influence of estrogen depends upon the long-term effects of an animal's metabolic state.     

Overcompensation of food intake following brief periods of food restriction

Four adult female Sprague-Dawley rats, maintained on an ad lib feeding schedule were deprived for either 0, 0.5, 1, 2, 4, 6, or 8 hours during the dark phase of the day-night cycle. It was found that the latency to initiate the first meal following the deprivation was independent of the previous deprivation interval. The animals were found to overcompensate for the periods without food by eating a large initial meal that increased proportionately in size with the duration of food restriction. Furthermore, the animals continued to overeat throughout the day. This deprivation-induced overeating by the animals resulted in an overcompensation in total food consumption that was 21–56% greater than on control days. The role of food intake as a regulator of body weight is discussed.     

Effects of dietary caloric density on feeding behavior in Mongolian gerbils (Meriones unguiculatus)

Total daily energy intake, water intake, body weight, and meal patterns were studied in Mongolian gerbils as a function of dietary caloric density. On diets ranging in caloric density from 2.25 kcal/g to 6.09 kcal/g, gerbils consumed an average of 40 kcal per 100 g of body weight per day. In comparison to gerbils fed ground Purina Laboratory Chow (4.2 kcal/g), gerbils presented with diets diluted with nonutritive cellulose increased food intake in proportion to the percentage of cellulose added. Gerbils given diets in which the caloric density was increased by the addition of fat, decreased food intake as a direct function of the added fat. Water intake was increased on the calorically diluted diets, and decreased on the concentrated diets. Body weight did not vary as a function of dietary conditions. On a standard pelleted diet (Noyes), gerbils ate approximately 18 meals a day. Average meal size was 0.4 g. When presented with calorically diluted pellets, gerbils maintained daily energy intake by increasing both meal frequency and meal size. There were no differences in food intake, meal frequency or meal size between the light and dark portions of the 24-hr cycle.     

Diet-induced thermogenesis and cumulative food intake curves as a function of familiarity with food and dietary restraint in humans.

Cumulative food intake curves and diet-induced thermogenesis were recorded in women during four-course solid-food lunches, consisting of familiar and unfamiliar food, offered in ad lib or restricted portions, in order to assess a possible relation between eating behaviour on the one hand and a reflection of internal processes and subject characteristics on the other. The subjects were characterized as normal weight restrained, normal weight unrestrained, and overweight restrained. A negative relation was found between degree of restraint and deceleration of the cumulative food intake curve during the ad lib courses of any menu, and between degree of restraint and diet-induced thermogenesis (p less than 0.001). Consequently, a positive relation was found between deceleration of the cumulative food intake curves during the ad lib courses of any menu and diet-induced thermogenesis (p less than 0.001). Diet-induced thermogenesis during the first serving of a meal consisting of unfamiliar food was significantly higher in all groups than during the other two times, when meals consisting of more familiar food were served (+0.98%; 0.71%, p less than 0.05).     

Palatability and intake relationships in free-living humans. characterization and independence of influence in North Americans

In order to investigate palatability influences on the ad lib eating behavior of free-living humans, 564 participants were paid to maintain food intake diaries for 7 days. They recorded their intake along with a global rating of the palatability of the entire meal on a seven-point scale. It was found that most meals that are self-selected are palatable and that only 9.3% are rated as unpalatable. Meals that were highest in palatability were 44% larger than meals that were low in palatability, but palatability only accounted for around 4% of the variance in meal sizes. Multiple regression demonstrated that palatability appears to act on intake independent of the levels of other influential factors. These results were very similar to those observed for the French and suggest that palatability operates similarly on intake regardless of culture. Palatability appears to be an influence on the amounts ingested by free-living humans in their natural environments but appears to be only one of many influential factors and accounts for only a small proportion of the variance in intake.     

Effects of portal volatile fatty acid infusions on meal patterns and blood composition in goats

Adult goats, provided with permanent jugular and portal vein catheters, were used to study whether circulating volatile fatty acids (VFA) or lactate might act as feedback signals in the control of meal size and/or frequency. Subjects were fed ad lib a pelleted diet supplemented with 100 g hay. Feed intake was recorded continuously. Portal infusions, mimicking the normal route of absorption, were made at a constant rate during 4 hours with isotonic or slightly hypertonic solutions of sodium salts of VFA or lactate, and their effects on feeding behavior and peripheral blood were determined. In spite of high blood concentrations reached, infusion of acetate, propionate, n-butyrate, isobutyrate or lactate did not change total 4-hr feed intake, meals size or intermeal interval. Neither did infusion of mixtures of VFA affect meal patterns. It is concluded that, if circulating VFA or lactate play a role at all in the control of feeding in the goat, the feedback signal does not arise from portal or peripheral blood.     

Feeding and drinking patterns in young pigs

Feeding and drinking patterns of six immature female pigs, weighing from 10 to 130 kg, operantly obtaining feed and water at a fixed ratio of 10, were determined. It was found by log survivorship analysis that 10 min was the minimum interbout interval defining separate eating bouts. As the pigs grew through this weight range, daily feed intake increased nearly threefold, while eating bout frequency fell from 14 to 7 per day; consequently both eating bout size and interbout interval increased. However, bout size was increased primarily by an increased rate of eating during bouts without any consistent increase in bout duration. Neither premeal nor postmeal intervals were correlated with meal size. Of the pigs' daily water intake, 75% was closely associated with eating bouts and over 1/3 of this (25%) was preprandial. Sixty-four percent of daily food intake and 68% of water intake was during the 12-hr light period. Nocturnal eating bouts were less frequent, but larger.     

Returning 'cafeteria-fed' rats to a chow diet: negative contrast and effects of obesity on feeding behaviour

Two experiments examined the feeding behaviour and body weight changes of rats returned to a standard chow diet after prolonged periods of cafeteria feeding. In the first, both overweight (ad lib fed) and 'normal' weight (fed a restricted ration of cafeteria foods) cafeteria rats became hypophagic compared to chow-fed rats following their return to chow feeding. However, the overweight rats' hypophagia was initially more severe and was longer lasting. In the second experiment, analysis of meal patterns recorded throughout the first 4 weeks on chow after 26-32 weeks of ad lib cafeteria feeding showed that the hypophagia was due to a reduction in mean meal size (MMS) and meal frequency (MF). Food intake and MMS subsequently recovered to within control levels (by 2-3 weeks), but MF remained persistently low. There was a decrease and then a recovery in eating rate (ER) which paralleled the changes in MMS. The previously cafeteria-fed rats lost only 60% of their excess body weight. These findings are interpreted in terms of a negative contrast effect (changes in MMS and ER) and an inhibitory action of increased adiposity on feeding (affecting mainly MF).     

Ecological determinants of reinforcement in the guinea pig

The hypothesis that constraints on the parameters of free feeding are the source of motivation in feeding behavior was explored in Guinea pigs. The effect of effort (FR size) on meal frequency, meal size and rate of eating was investigated when reinforcement consisted of an entire meal or a small portion of a meal. Frequency of feeding decreased and the duration and rate of eating increased when an entire meal was available. Frequency of meals was unaffected and rate of lever pressing and duration of meals increased when reinforcement consisted of a single food pellet. These data were taken to argue that there is a common pattern of changes in feeding behavior across species with respect to these variables and the value of these variables can be taken to describe the properties of different ecological niches.     

Effect of food deprivation and maintenance diet composition on fat preference and acceptance in rats

High-fat diets typically elicit greater kcal intake and/or weight gain than low-fat diets. Palatability, caloric density, and the unique postingestive effects of fat have each been shown to contribute to high-fat diet hyperphagia. Because long-term intake reflects the sum of many individual eating episodes (meals), it is important to investigate factors that may modulate fat intake at a meal. The present studies used high-fat (hi-fat) and high-carbohydrate (hi-carb) liquid diets (both 2.3 kcal/mL) to assess the effect of hunger level (0 versus 24-h food deprivation) and fat content of the maintenance diet (12 versus 48%) on fat preference (when a choice among foods is offered in a two-bottle test), and acceptance (only one food offered) in male rats. Preference for hi-fat relative to hi-carb (two-bottle test) was enhanced by 24-h food deprivation, and by a high-fat maintenance diet. In contrast, neither deprivation nor maintenance diet composition influenced relative meal size (one-bottle test) of hi-fat and hi-carb: irrespective of test conditions, meal size of hi-fat was bigger than meal size of hi-carb.     

Meal patterns of pygmy goats fed hay and concentrate ad lib

The meal patterns of pygmy goats fed hay and pelleted concentrate ad lib were recorded and analyzed. The pygmy goats consumed 8 hay meals [6 during the light phase (= light)/2 during the dark phase (= dark)] and 10 concentrate meals (7 during light/3 during dark) during 24 hr (12 hr light/12 hr dark). Sixty-two percent of hay and 74% of concentrate intake occurred during light. Total 24-hr hay (280 g) and concentrate (264 g) intakes were similar, but concentrate was preferred during dark. Concentrate meals were smaller during light than during dark. The mean feeding rate (g/min) within meals for both hay and concentrate was higher during dark than during light. Meal size and duration of postmeal interval were positively correlated for concentrate but not for hay. No significant positive correlation was found between meal size and duration of premeal interval. Separate analysis of diurnal and nocturnal meals indicated that the postmeal correlation for concentrate was evident primarily during dark. The results demonstrate that food intake in pygmy goats shows distinct diurnal variations and suggest that food intake in ruminants is regulated from meal to meal, with different factors prevailing during light and dark.     

Role of rumen fluid hypertonicity in the dehydration-induced hypophagia of cows

Three experiments were performed in non-lactating, rumen-fistulated cows to assess the role of rumen fluid hypertonicity in dehydration-induced hypophagia. First, the course of rumen fluid and plasma osmolality before and after an individual test meal was recorded when water was offered ad libitum and on the fifth day of a 65% water restriction period. Then, the effects of intraruminal water infusions on food intake were examined in dehydrated cows. Finally, two doses of the local anesthetic mepivacaine HCl were given into the rumen in an attempt to inactivate the osmosensors potentially involved in dehydration-induced hypophagia. Water restriction reduced test meal size and increased rumen fluid and plasma osmolality. Despite the smaller meal, the prandial increase in rumen fluid osmolality was more pronounced during water restriction than with water ad libitum. Independent of treatment, the test meal had no effect on plasma osmolality. Intraruminal water infusions during water deprivation decreased rumen fluid osmolality below the control level and normalized food intake. Injection of 2 or 4 g mepivacaine/cow into the rumen did not attenuate dehydration-induced hypophagia. All in all, these results suggest that rumen fluid hypertonicity, perhaps in concert with plasma hypertonicity, contributes to the early satiation induced by dehydration.     

Energetics of meal patterns in rats

Meal patterns in rats were examined as functions of the caloric density and availability of the diet. Three diets were used, a standard laboratory diet (3.6 kcal/g), a calorically diluted diet (2.7 kcal/g), and a calorically concentrated diet (4.5 kcal/g). After obtaining ad lib measures of meal patterns on each diet availability of food was constrained by requiring the rats to complete fixed ratio requirements of barpresses to obtain access to a meal. On all 3 diets, meal frequency decreased, while meal size and duration increased as functions of the ratio requirement. Under ad lib conditions and low ratio requirements, in comparison to the standard diet, meal frequency was greater on the diluted diet and less on the concentrated diet. Meal size did not vary as a function of diet on low ratio schedules. At high ratio requirements, rats continued to maintain caloric intake on the diluted diet by increasing meal frequency. On the concentrated diet, however, rats maintained intake at high ratio values by decreasing meal size rather than meal frequency. The results indicate that the rat can adopt a variety of strategies to solve the problem of controlling energy intake constant across the daily feeding cycle.