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Eating disorders are associated with a range of abnormalities in eating behavior. Some individuals consume large amounts of non-caloric artificial sweeteners, suggesting abnormalities in appetitive responding. The current study aimed to quantify hedonic and motivating effects of artificial sweetener in individuals with and without an eating disorder. Two laboratory studies were conducted. Hedonic preference was estimated using the number of artificial sweetener packets (0 to 10) added to unsweetened cherry flavored Kool-Aid (study 1). Motivation to obtain sweetener was assessed by a progressive ratio (PR) work task (study 2). Ninety-three participants (25 anorexia nervosa restricting type (AN-R), 23 AN binge/purge type (AN-B/P), 20 bulimia nervosa (BN), and 25 normal controls (NC)) completed the study. No significant difference in hedonic preference was found among participant groups. Work completed at the PR task ranged from 0 to 9500 key-board presses. The AN-B/P group had a significantly higher breakpoint and performed significantly more work for sweetener compared to the BN and NC groups. Among AN-B/P and AN-R participants, the preferred number of Equal packets was significantly correlated with the breakpoint and total work. The increased amount of work for sweetener among individuals with AN-B/P supports an enhanced reward value of sweet taste in this population, and suggests that the characteristic food avoidance in AN cannot be accounted for by decreased reward value of all taste-related stimuli. This study also supports the novel application of a PR ratio task to quantify the motivating effect of sweet taste among individuals with an eating disorder.

This study examined how pharmacological and behavioral manipulations affect appetitive and consummatory aspects of feeding of baboons. Baboons have access to food 24 h each day, but they must complete a two-phase operant procedure in order to eat. Responding on one lever during a 30-min appetitive phase was required before animals could start a consumption phase, i.e. a meal, where responding on another lever led to food delivery. Responding during the appetitive phase resulted in presentations of food-related stimuli only. Decreasing session length, increased appetitive behavior and increased meal size. Limiting the number of meals to a single 90 min meal each day but increasing the number of food pellets the animals received increased the size of meal, but did not increase appetitive behavior. These findings suggest that time since the previous meal has a greater effect on appetitive behavior than the size of the previous meal. Amphetamine (AMPH), which increases dopamine, decreased food intake at doses that did not affect appetitive behavior, indicating that appetitive and consummatory aspects of eating can be pharmacologically differentiated. Increasing how frequently animals could earn food-related stimuli in the appetitive phase and food in the consummatory phase increased both appetitive and consumatory behavior. Under these conditions, AMPH nearly doubled appetitive behavior at doses that decreased food intake by nearly 50 percent. When animals had one meal, of self-determined duration, meal size increased without affecting appetitive behavior, further demonstrating that appetitive behavior can be independent of the size of the previous meal and not predictive of the size of the subsequent meal. Under these conditions, AMPH decreased food intake at doses that did not affect appetitive behavior. In contrast, dexfenfluramine (DFEN), which increases serotonin, decreased both appetitive and consumatory behavior. Thus, it is possible to independently manipulate the appetitive and consummatory aspects of eating using both pharmacological and behavioral interventions indicating that it may be possible to develop medications that selectively affect appetitive or consummatory aspects of eating.

The effects of planned meals, varying in carbohydrate (CHO), fat and caloric content, on psychomotor performance by male subjects with unrestricted access to commercially-available foods was investigated in two residential studies. In the first study, two groups of three subjects (n = 6) completed psychomotor tasks before and after consuming a lunch consisting of 431 or 844 kcal, with caloric differences produced through covert changes in either fat or CHO content. The effects of each of four lunch conditions (low-fat, high-fat, low-CHO, high-CHO) were determined for three consecutive days. In the second study, two groups of three subjects (n = 6) received breakfast, lunch and an afternoon snack and completed psychomotor tasks after breakfast and lunch. Cumulative caloric content of the three eating occasions was approximately 700, 1200 or 1700 kcal (low, medium or high), again with differences resulting from covert changes primarily in either fat or CHO content. The effects of each of six food conditions were determined for two consecutive days. While changes in some aspects of performance were altered after meals, the effects were not related to the CHO, fat or caloric content of the meal. When subjects have unrestricted access to commercially-available foods, neither calories nor the relative fat or CHO content of normal meals influence human psychomotor task performance.

Six subjects participated in a residential study assessing the effects of consuming beverages containing energy derived from ethanol or dextrose on total energy and macronutrient intake. On certain days, subjects had to consume four beverages containing a total of approximately 2400 or 4600 kJ, equivalent to 22% and 42% of energy intake under conditions in which no-beverages were required. Each of four conditions (2400 kJ ethanol, dextrose; 4600 kJ ethanol, dextrose), and a no-beverage control condition was examined for 2 days. Subjects compensated for approximately 37% of the energy contained in the beverages such that total intake increased by 13% under the 2400 kJ conditions and 27% under the 4600 kJ conditions. There was no differential effect of ethanol content on energy intake. Cumulative intake curves indicated that caloric compensation was minimal following the consumption of beverages in the evening. While all of the beverage conditions significantly decreased energy intake derived from carbohydrate, the proportion of energy derived from fat, carbohydrate, and protein without the energy content of the beverages was essentially unaffected by dextrose- or ethanol-containing beverages. These results suggest that the effects of ethanol on intake of other foods can be accounted for by the energy content of ethanol as a beverage and by ethanol consumption in the evening when there is little time for daily caloric compensation, rather than by the pharmacological effects of ethanol.

In a study examining “demand” for food, the responses of six adult male baboons ( Papio c. anubis ) were maintained under a fixed ratio schedule of food reinforcement during daily 22-h experimental sessions. Completion of the ratio requirement resulted in the delivery of a single 1-g food pellet. Caloric intake was studied under four food-access conditions: a single source of 1-g food pellets, two sources of pellets with different response costs, one source of pellets and one source of dextrose solutions with different response costs, or a single source of multiple pellets. Total daily caloric intake under minimal response-cost conditions did not vary across these four conditions. Increasing the response requirement for a single pellet decreased daily food intake. Compared to this single-pellet condition, increasing the response requirement: (a) decreased intake of multiple pellets to a much smaller extent; (b) decreased pellet intake to a larger extent when dextrose was available on an alternate lever and (c) decreased pellet intake to the greatest extent when pellets were available on an alternate lever. Changes in pellet intake were fitted to a theoretical equation derived by Hursh et al . (1988) to describe changes in demand for a commodity. Increasing the number of pellets per delivery decreased the rate of change in intake as cost increased, indicating decreased elasticity. Dextrose availability increased the rate of change in intake as cost increased, indicating increased elasticity. Availability of an identical food source increased the initial slope of intake without effecting the rate of change, thus also increasing elasticity. Mathematical analysis of demand curves provide a means of comparing the effects of diverse environmental manipulations on feeding behavior.

Two groups, each consisting of three normal weight, male research volunteers, lived continuously in a residential laboratory for 15 days. All contact with the experimenters was through a networked computer system and subjects' behaviors, including food intake, were continuously recorded. During the first part of the day, subjects remained in their private rooms doing work activities. During the remainder of the day, they had the option to socialize with each other. A wide variety of food items were continuously available. Subjects controlled their own patterns of food intake, and could consume any item, or number of items, at any time during the day. Beverages containing d-amphetamine (10 mg per 70 kg) or placebo were consumed daily at 0930 and 1630 hrs. Amphetamine significantly reduced total daily caloric intake to about 70% of placebo levels. The reduction in intake was a consequence of a decrease in number of eating occasions per day; no changes in mean intake per occasion were observed. Amphetamine produced similar decreases in the daily number of snack and meal items, and in protein, fat, and carbohydrate intake. These results demonstrate that amphetamine has significant effects on human food intake, and the study of human feeding behavior under similar naturalistic conditions should provide important information about the behavioral actions of drugs affecting food intake.

Ten male and one female normal-weight research volunteers, participating in a 16-day residential study, received oral fluoxetine (40 mg) or placebo at 0930 daily. Food intake, performance and subjective ratings were measured throughout the day. The interaction between fluoxetine and carbohydrate consumption was examined by providing subjects diets that engendered varied levels of carbohydrate intake. When subjects received placebo and had access to a regular diet, they consumed 3400 kcal day−1(53% carbohydrate, 34% fat, 13% protein); and fluoxetine decreased caloric intake to 2770 Kcal, without affecting macronutrient contribution. Caloric intake (2730 Kcal; 67% carbohydrate) under the high-carbohydrate condition when subjects received fluoxetine was not different from intake under the regular-diet fluoxetine condition. Subjects reported that the high-fat (low-carbohydrate) diet was less palatable and consumed 2975 Kcal under placebo conditions (35% carbohydrate); fluoxetine decreased caloric intake by an additional 400 Kcal without affecting macronutrient contribution. There was no evidence that carbohydrate intake modulated the effects of fluoxetine. Fluoxetine decreased food intake by decreasing the number of eating occasions. Performance and subjective measures were not significantly altered by fluoxetine compared to placebo. Thus, there was no evidence of a specific effect of fluoxetine on macro?nutrient consumption, nor were the effects of fluoxetine altered by the macro?nutrient composition of the available diet.

Food intake of seven adult male baboons ( Papio cynocephalus anubis ) was monitored during daily 22-h experimental sessions. Food was available under a two-component operant schedule. Following completion of the first “procurement component” response requirement, access to food, i.e. a meal, became available under the second “consumption component,” during which each response produced a 1-g food pellet. After a 10-min interval in which no response occurred, the consumption component was terminated. The effects of carloric preloads on food intake were determined by giving each baboon a meal of preferred foods 45–60 min prior to the start of the daily session. Caloric preloads decreased food intake during the first 8 h of the session, but had no effect on intake during the entire session. The effects of acute deprivation on food intake were determined by terminating sessions after a baboon had consumed 20–80% of baseline intake, and by starting a session 4–12 h late. Deprivation did not increase subsequent food intake. The effects of the availability of an alternative source of calories on total daily intake were determined by providing access to a dextrose solution. Baboons decreased intake of solid food in accordance with the caloric intake from the dextrose solutions by decreasing the number of meals. Finally, the effects of providing a diet of higher caloric density on food intake were determined. Two of the four baboons tested in this procedure maintained baseline levels of daily caloric intake, while the other two baboons increased daily caloric intake. In summary, free-feeding baboons were relatively insensitive to acute changes in feeding conditions, but were sensitive to long-term changes in the caloric content of available foods.

Six adult male research volunteers, in two groups of three subjects each, lived in a residential laboratory for 13 days. All contact with the experimenter was through a networked computer system and subjects' behaviors, including food intake, were continuously recorded. During the first part of the day, subjects remained in continuously recorded. During the first part of the day, subjects remained in their private rooms doing planned work activities, and during the remainder of the day, they were allowed to socialize. Two cigarettes containing active marijuana (2.3% delta 9 THC) or placebo were smoked during both the private work period and the period of access to social activities. Smoked active marijuana significantly increased total daily caloric intake by 40%. Increased food intake was evident during both private and social periods. The increase in caloric intake was due to an increased consumption of snack foods as a consequence of an increase in the number of snacking occasions. There was no significant change in caloric consumption during meals. The principal increase within the category of snack foods was in the intake of sweet solid items, e.g., candy bars, compared to sweet fluid, e.g., soda, or savory solid items, e.g., potato chips. Increases in body weight during periods of active marijuana smoking were greater than predicted by caloric intake alone.

Food intake of four adult male baboons ( Papio c. anubis ) was monitored during daily experimental sessions lasting 22 h. Food was available under a two-component operant schedule. Following completion of the first “procurement component” response requirement, access to food, i.e. a meal, became available under the second “consumption component” during which each response produced a 1-g food pellet. After a 10-min interval in which no response occurred, the consumption component was terminated. A long-acting cholecystokinin (CCK) analog U-67827E (U-67: 0.80–3.2 μg/kg) was administered, in the thigh muscle, at 1100 hrs immediately prior to the start of the daily session on Tuesdays and Fridays. U-67 significantly reduced intake during the first 8-h of the session, and intake during the entire 22-h session. The decreased intake was due to a significant decrease in the size of the first meal of the session as a consequence of decreased duration of feeding without a change in response rate. U-67 also produced dose-dependent increases in latency to the first meal of up to 2.5 h. These results demonstrate that a long-acting CCK analog decreases food intake over a prolonged period of time in a naturalistic feeding situation. In addition, the effects of U-67 were limited to the consumption component, suggesting that this CCK analog affected food intake by interacting with physiological mechanisms specifically associated with feeding.

Six adult male research volunteers, in two groups of three subjects each, lived continuously in a residential laboratory for 14 days. All contact with the experimenters was through a networked computer system and subjects' behaviors, including food intake, were continuously recorded. During the first part of the day, subjects remained in their private rooms doing work activities. During the remainder of the day, they had the option to socialize with each other. A wide variety of food items were continuously available. Subjects were in complete control of their pattern of food intake and could consume any item, or number of items, at any time during the day. On days 6 through 11, reduced calorie versions of approximately one third of the food items were covertly substituted for the regular caloric content items. This manipulation decreased intake from the reduced-calorie group of foods by 500 kcal. The subjects immediately and completely compensated for the loss of calories by increasing the number of non-calorie-manipulated food items consumed. When regular calorie foods were again available during the last 3 days of the experiment, subjects failed to compensate for this increase in caloric intake. Thus, under conditions of unlimited access to food, human volunteers completely compensated for caloric dilution, but were less accurate in responding to increases in caloric intake.