Progressive ratio (PR) schedules and the sipometer: Do they measure wanting, liking, and/or reward? A tribute to Anthony Sclafani and Karen Ackroff.

This paper honors the contributions made by Anthony (Tony) Sclafani and Karen Ackroff to both the Columbia University Seminar on Appetitive Behavior and to the field of ingestive behavior in general. We review their use of the progressive ratio (PR) licking paradigm, to determine whether the taste of sucrose, independent of its post-ingestive effects, is always positively reinforcing in animals. They demonstrated a monotonic increase in licking as concentration increased, and obtained results identical to those obtained with a lever-pressing paradigm, but licking was easier and more natural than lever pressing. The PR paradigm was translated to evaluate liquid food reward value in humans. An instrument (the sipometer) was devised that initially permitted a few seconds access to small amounts of a sweet beverage as the participants increased the time to obtain it in 3-5-sec increments. The device went through two refinements and currently delivers the reinforcer and measures the pressure exerted to obtain it. The sipometer is compared with other techniques for measuring motivation and reward. The use of the sipometer and the PR method are discussed in relation to the theoretical challenges inherent in measuring motivation and pleasure, from both psychological and behavioral economics perspectives, and why it is or is not important to separate these processes for both theoretical and practical applications.

Computerized measurement of anticipated anxiety from eating increasing portions of food in adolescents with and without anorexia nervosa: Pilot studies.

Dieting and excessive fear of eating coexist in vulnerable individuals, which may progress to anorexia nervosa [AN], but there is no objective measure of this fear. Therefore, we adapted a computer program that was previously developed to measure the satiating effects of foods in order to explore the potential of food to induce anxiety and fear of eating in adolescent girls. Twenty four adolescents (AN) and ten healthy controls without eating disorders rated pictures of different types of foods in varying sized portions as too large or too small and rated the expected anxiety of five different portions (20-320 kcal). Two low energy dense (potatoes and rice) and two high energy dense (pizza and M&Ms) foods were used. The regression coefficient of line lengths (0-100 mm) marked from "No anxiety" to "this would give me a panic attack", regressed from portions shown, was the measure of "expected anxiety" for a given food. The maximum tolerated portion size [kcal] (MTPS), computed by method of constant stimulus from portions shown, was significantly smaller for high energy dense foods, whereas the expected anxiety response was greater, for all foods, for patients compared to controls. For both groups, expected anxiety responses were steeper, and maximum tolerated portion sizes were larger, for low, than high, energy dense foods. Both maximum tolerated portion size and expected anxiety response were significantly predicted by severity of illness for the patients. Those who had larger maximum tolerated portion sizes had smaller anticipated anxiety to increasing portion sizes. Visual size had a greater influence than energy content for these responses. This method could be used to quantify the anxiety inducing potential of foods and for studies with neuro-imaging and phenotypic clarifications.

Elasticity in portion selection is predicted by severity of anorexia and food type in adolescents.

The size of portions that people select is an indicator of underlying mechanisms controlling food intake. Fears of eating excessive portions drive down the sizes of portions patients with anorexia nervosa (AN) can tolerate eating significantly below those of healthy controls (HC) (Kissileff et al., 2016). To determine whether patients with AN will also reduce the sizes of typical or ideal portions below those of controls, ANOVA was used to compare maximum tolerable, typical, and ideal portions of four foods (potatoes, rice, pizza, and M&M's) in the same group of 24 adolescent AN patients and 10 healthy adolescent controls (HC), on which only the maximal portion data were previously reported. Typical and ideal portion sizes did not differ on any food for AN, but for HC, typical portions sizes (kcals) became larger than ideal as the energy density of the food increased, and were significant for the most energy dense food. Ideal portions of low energy dense foods were the same for AN as for in HC. There was a significant 3-way (group × food × portion type) interaction, such that HC selected larger maximum than typical portions only for pizza. We therefore proposed that individuals of certain groups, depending on the food, can be flexible in the amounts of food chosen to be eaten. We call this difference between maximum-tolerable, and typical portion sizes selected "elasticity." Elasticity was significantly smaller for AN patients compared to HC for pizza and was significantly inversely correlated with severity of illness. This index could be useful for clinical assessment of AN patients, and those with eating problems such as in obesity and bulimia nervosa and tracking their response to treatment.

A sipometer for measuring motivation to consume and reward value of foods and beverages in humans: Description and proof of principle.

New methods, derived from animal work, for measuring food reward value (i.e. reinforcing value of food), and motivation (i.e. strength of desire) to consume, in humans are described and validated. A sipping device (sipometer) was developed that permits access to a liquid food or beverage on two reward schedules: continuous reinforcement (CR) and progressively increasing time spent exerting pressure on a straw (PR-schedule). In addition, a pictorial scale showing a cup, from which the 'amount wanted' could be marked was used to pre-test potential consumption. Intake, time spent sipping, breakpoint, and pressure exerted were the main dependent variables measured. Three pilot experiments were conducted. In Experiment 1, participants (n=8) consumed yogurt shakes after a 1-h or 21-h food deprivation period on both schedules. In Experiment 2, participants (n=8) sham-consumed (i.e. spit out) sweet and non-sweet beverages, utilizing both schedules. In Experiment 3, sham-consuming sweet and non-sweet beverages on both schedules and working for shake on the PR schedule were repeated, after three nights of either habitual sleep or short sleep duration (n=7) in a crossover design. In Experiment 1, participants sipped longer after 21-h vs. 1-h of food deprivation (13±3.0 vs. 8.0±2.1s; p=0.04), on the PR schedule. In Experiment 2, sham-intake (p=0.01) and sipping time (p=0.04) were greater for sweet than non-sweet beverages on the PR schedule and a similar, though not conventionally significant, effect was observed for exerted pressure (p=0.09). In both Experiment 2 and Experiment 3 after habitual sleep, on the PR schedule, cumulative pressure difference between sweet and non-sweet beverage increased with difference in amount wanted in the taste test. In contrast, after short sleep participants were less willing to work for sweet taste as their wanting increased, suggesting that sleep deprivation raises desire, but lowers behavioral output. Taken together these results demonstrate that the sipometer and associated ratings are reliable and useful measures of motivation to consume and reward value in humans. Participants were more motivated to obtain access to sweet beverages, especially when these were better liked than to obtain access to non-sweet beverages.

Gastric compliance in bulimia nervosa.

Bulimia nervosa (BN) is a psychiatric illness characterized by eating binges followed by inappropriate behavioral attempts to compensate for the binges, usually vomiting or laxative abuse. Patients with BN have disturbances in the development of satiety during a meal as well as disturbances in functions of the upper gastrointestinal tract such as slowed gastric emptying, impaired gastric accommodation reflex and blunted cholecystokinin release. The present study examined gastric compliance and sensory responses to gastric distention in women with BN and controls. Sixteen women with BN and 13 healthy control subjects swallowed an inflatable bag that was placed in the proximal stomach. The bag was inflated to produce increasing steps of pressure against the stomach wall, before and after consumption of a 200 ml (200 Kcal) liquid meal. Pressure and volume were recorded for 2-min periods, beginning at 0 mm Hg pressure and increasing in steps of 2 mm Hg until subjects reported discomfort, gastric volume reached 600 ml, or pressure reached 20 mm Hg. At each pressure step subjects made sensory ratings. Gastric compliance was calculated as the slope of the best-fit straight line of each subject's gastric volume vs. gastric pressure. There was a significant postmeal increase in gastric compliance in both groups of subjects but there was no difference in compliance between patients with BN and controls. Patients with BN appeared to have diminished sensitivity to gastric distention. In conclusion, although other studies have described gastrointestinal abnormalities associated with BN, the current study found gastric compliance of patients with BN to be normal.

Eating behavior of women with bulimia.

To obtain objective information about binge- and non-binge-eating behavior, 12 women with bulimia and ten women without eating problems (controls) were asked to eat four meals in a structured laboratory setting, on separate nonconsecutive days. The same instructions were given to both groups. On two days, they were asked to eat a normal amount, and on two days, they were asked to eat as much as they could, ie, to binge. For each type of instruction, they were given a single- and a multiple-course meal. The patients ate significantly more than the controls when asked to binge, both on the multiple-course meals that they rated as typical of binges and on the single-course meals. When they were asked to eat normally, there was no significant difference in intake between patients and controls on either single- or multiple-course meals. After all meals, hunger ratings of patients were significantly higher than hunger ratings of controls. There was also a significant positive correlation between intakes of single- and multiple-course binge meals and an inverse correlation between intake of multiple-course binge meals in bulimic patients and their rating of how well they controlled their eating. Thus, a structured laboratory eating situation can be used to reveal differences between bulimic and normal individuals and has the potential for assessing clinical status and exploring mechanisms responsible for binge eating.

Satiating efficiency and a strategy for conducting food loading experiments.

The general hypothesis is proposed that foods vary along a small number of dimensions, such as nutrient composition, energy content, or weight, each of which makes a potentially measurable, but presently unknown, contribution to the satiation process. Because of the differential contributions of each of these dimensions (or factors), foods will vary in the effectiveness with which they induce satiety. Predictions of this hypothesis can best be tested by using the preloading strategy, in which preloads, varied along one dimension at a time, are given on different occasions in amounts which vary along the dimension being studied, and the experimental subject is permitted to eat the test meal following the preload until satiated. The contribution of that dimension is then assessed by the equation relating intake of the test meal to the magnitude of preload along the chosen dimension. The negative of the slope of the intake-preload equation is an index we call "satiating efficiency" of the magnitude of the satiating effect per unit of the chosen dimension. The satiating efficiency therefore provides a method of comparing the ability of different foods to induce satiety, along any dimension. This strategy can be used theoretically to measure the contribution of various dimensions of food to satiety. Practically it could be used to improve the satiating efficiency of foods designed for appetite control, by incorporating into the food, components which are high in satiating efficiency per unit of energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Microstructural analyses of human ingestive patterns: from description to mechanistic hypotheses.

Continuous automated weighing of food while subjects ate was used to test the hypothesis that failure to slow eating rate during a meal indicated a deficient response to satiety signals in obese patients. Cumulative intake curves were fitted to a quadratic equation. The physical form of the food and its palatability were a greater influence on the equation's parameters than the subjects' body weights, and the hypothesis was abandoned for several years (1984-1993). The hypothesis was revived with modifications when we discovered disturbances in eating behavior in patients with bulimia nervosa. The new hypothesis was that overeating was attributable to subjects' inability to detect or respond to satiety-related signals after eating large amounts of food. Patients with eating disorders showed lower ratings of satiety after eating the same amounts of food as controls, but only after eating more than normal. In conclusion, microstructural examination of eating behavior may be more useful for tests of specific hypotheses about the control of eating than as a description of clinical disturbance.

Effects of physical state (liquid-solid) of foods on food intake: procedural and substantive contributions.

Two types of procedures are described for the study of the effects of food attributes on food intake. One is concurrent evaluation in which the attribute is placed in the food, and the amount consumed is measured. The other is the preloading paradigm in which a food containing the attribute is given before a test meal and intake of the test meal is measured. From our work with both types of procedure in which we used foods in both solid and liquefied form, we conclude that the effects of food attributes on intake will differ depending on which procedure is used. Concurrent evaluation is recommended when the time course of the attribute is short-lived (few seconds to a minute). Preloading is the procedure of choice when the attribute's effect is longer-lasting (several minutes to hours). When the same food was served in either solid or liquefied form, there was no difference in intakes of the two versions, but for liquefied form, the rate of consumption was faster, and meal duration was shorter, than for the solid. When a completely liquefied preload (soup) was given, intake in the following test meal was less for the same caloric load than when the preload was only partly in liquid form. Liquefied foods may be more efficient in producing satiety, as measured by food intake reduction, than solids. Because the two preloads were different across dimensions other than solid-liquid, more investigation of these other dimensions is needed.

Physiology of energy intake: an inventory control model.

An inventory control model is used to describe the regulation of depot fat and contribution made to the satiation process by putative feedback signals. In the two bin inventory control system, adipose tissue is viewed as a large storage reservoir which is periodically refilled by means of adjustments made in meal consumption. The gastrointestinal tract is viewed as a smaller bin which triggers renewed food ingestion when it becomes partially emptied. However, reduction in the contents of the adipose tissue bin below a critical level (reorder point quantity) generates a signal to the brain that appropriately modulates meal size and intermeal interval. Because this model evolved to cope with worst case situations, a strong bias for storage in time of plenty is inherent in the system. This fact helps to account for the high prevalence of obesity in energy-rich societies, where, in contrast to the situation that obtains in primitive societies, the energy cost of obtaining food is minimal.

Patterns of food selection during meals in women with bulimia.

Eating behavior of women with bulimia was compared with that of control subjects who had no eating disorders. Both groups were presented with two buffet-style multiple-item meals. In one meal subjects were instructed to eat normally and in the other they were instructed to eat as much as they could. The eating patterns of patients differed from control subjects in the quantity of food selected and in the rate of eating. During the binge meal, patients spent more of their meal time eating dessert and snacks than did control subjects and began their dessert and snack consumption earlier than control subjects. Patients distributed their meat consumption more evenly across the meal, whereas control subjects ate meat predominantly early in the meals. Most patients consumed either more or less than control subjects when not binge eating, indicating that the eating disturbances in bulimic patients are not confined to episodes of binge eating.

C-terminal octapeptide of cholecystokinin decreases food intake in man.

In comparison with a saline infusion, the infusion of the C-terminal octapeptide of cholecystokinin (4 ng/kg/min) decreased food intake by an average of 122 g in a group of 12 lean men without objective evidence of untoward side effects. Shapes of the cumulative intake curves under the two conditions were similar, but subjects ate less and stopped eating sooner when receiving octapeptide than when receiving saline. These results are consistent with the hypothesis that cholecystokinin is an endogenous signal for postprandial satiety. The results offer promise for the possible use of the octapeptide as an appetite suppressant.

Acute effects of exercise on food intake in obese and nonobese women.

The animal model of exercise-induced anorexia was employed in humans to develop a laboratory paradigm for studying the acute effect of exercise on food intake. Each of nine obese and nine nonobese women exercised either strenuously (90 W) or moderately (30 W) on a cycle ergometer for 40 min or rested in the laboratory on each of 3 nonconsecutive days. Intake of a liquefied test meal (1.04 kcal/g) eaten 15 min after exercise was significantly less after the strenuous (620 g) than after the moderate (754 g) exercise in the nonobese women but was no different after the two conditions (532 g after strenuous, 581 g after moderate) in the obese women. Heart rate and energy expenditure were increased in proportion to the exercise by the same amount in both groups. The results demonstrate for the first time that food intake is reduced immediately after strenuous exercise in nonobese women, as it is in animals, and validate the feasibility of this laboratory paradigm.

Lack of sustained increase in VO2 following exercise in fit and unfit subjects.

Thermogenesis after exercise was studied by measuring oxygen consumption in 23 subjects who were classified into three groups according to their routine level of physical activity. VO2 was first measured after a 30-minute rest period 4-hours after breakfast. Then each subject either exercised for 20 minutes at approximately the anaerobic threshold or on a separate non-exercise day remained recumbent. The subject then returned to, or remained, at rest. There was no significant difference in VO2 from the resting level from 40 minutes to 3 hours after exercise, between exercise and non-exercise days in any fitness group. Seven subjects also exercised for a longer period or at a higher intensity. Again, there was no significant difference in the time course of VO2 from 40 minutes to 220 minutes after exercise, between exercise and non-exercise days. Because no sustained effect of moderate or intense exercise on VO2 was demonstrated, we conclude that no appreciable caloric loss beyond that generated by the exercise period itself and the early recovery phase is found in either fit or unfit subjects. These data do not support claims for sustained increases in metabolic rate after exercise in weight-control programs.

Food selection and intake of obese women with binge-eating disorder.

We studied food selection and intake of 19 women [body mass index (in kg/m2) > 30] [corrected], 10 of whom met proposed DSM-IV criteria for binge-eating disorder (BED). All subjects ate two multicourse meals in the laboratory, and were given tape-recorded instructions at each meal either to binge or eat in a normal fashion. Subjects with BED consumed significantly more energy than did subjects without BED at both the binge [12,400 vs 8440 kJ (2963 vs 2017 kcal), P < 0.005] and normal [9810 vs 6870 kJ (2343 vs 1640 kcal), P < 0.02] meals. During the binge meal subjects with BED consumed a greater percentage of energy as fat (38.9% vs 33.5%, P < 0.002) and a lesser percentage as protein (11.4% vs 15.4%, P < 0.01) than did subjects without BED. There were no differences in macronutrient composition of food choices between groups in the normal meal. Obese women who meet criteria for BED show differences in both intake and macronutrient composition of food choices from obese women who do not meet these criteria when asked to eat in a laboratory setting, supporting the validity of this new diagnosis.

Postprandial cholecystokinin release and gastric emptying in patients with bulimia nervosa.

This study was designed to investigate the biological underpinnings of the observed deficit in satiety in patients with bulimia nervosa. Eight women with bulimia nervosa and 10 age- and weight-matched control subjects consumed three laboratory meals consisting of 200, 400, and 600 g of a radiolabeled liquid meal. For 1 h after each meal, blood samples were obtained at 10-min intervals for measurement of cholecystokinin concentration and gastric emptying was measured. Subjects also completed perceptual rating scales at 10-min intervals. Compared with control subjects, patients with bulimia nervosa showed a blunting of postprandial cholecystokinin release, particularly with larger meal sizes, as well as delayed gastric emptying. Increasing meal size was associated with increased desire to binge eat in patients but not in control subjects. These data lend support to a model in which increased gastric capacity, perhaps resulting from repeated binge eating, gives rise to delayed gastric emptying and blunted postprandial cholecystokinin release, leading to an impaired satiety response, which tends to perpetuate the illness.

Eating behavior in bulimia.

Despite our strong belief in the utility of laboratory studies of eating behavior, we also note several caveats on the data thereby obtained. First, it must be assumed that subjects' behavior is influenced by the laboratory environment and is not identical to eating behavior in a "normal" setting. Second, not all bulimic subjects who were screened for these studies actually participated, so that it is possible that the sample of patients from whom we obtained data differed in some ways from a general clinical population of women with bulimia. Nonetheless, we believe that our data provide compelling evidence that the disturbed eating behavior characteristic of bulimia nervosa can be profitably studied in the laboratory. Even under structured laboratory conditions, most bulimic patients rated one of their multicourse meals as typical of a binge, and, during that meal, consumed a much larger amount of food and ate more rapidly than did controls who were asked to overeat. The significant correlations between the sizes of the multicourse and single-course binge meals and between the size of laboratory binge meals and the size of the "naturally occurring" binge meals reported to the dietician suggest that a reproducible phenomenon is being examined. The results of our studies suggest that the abnormalities of eating behavior in bulimia nervosa cannot be viewed simply as a disturbance of carbohydrate consumption or even as the episodic consumption of a certain type of food. Rather, eating behavior in this syndrome appears more generally disturbed. The most striking difference between the binge and the nonbinge meals of bulimic patients and between the binge eating of patients and the overeating of normal persons is the amount of food consumed, not the macronutrient composition of the meals. In addition, for all four meal types, the patients were hungrier after the end of the meal than were the controls, even though the patients' average caloric intakes were generally larger and their average hunger ratings before the meals did not differ from those of the controls. Certainly, self-induced vomiting may contribute to this abnormality, but it was also observed after nonbinge meals when vomiting did not occur. Together, these data are consistent with the notion that the essential appetitive abnormality in bulimia nervosa lies in the control of the amount of food consumed, not in the consumption of a particular macronutrient or type of food. Patients with bulimia nervosa appear less responsive than normal to the signals that lead to the termination of a meal.(ABSTRACT TRUNCATED AT 400 WORDS)

The satiety effect of cholecystokinin: a progress report.

The satiety effect of cholecystokinin (CCK) that was first observed in rats has now been extended to chickens, rabbits, pigs, sheep, rhesus monkeys, lean mice, genetically obese mice and rats, neurologically obese rats, lean men and women, and obese men. The effect is specific and can be obtained in animals and humans without reports or signs of sickness. The mechanism of the effect is unknown, but the gastric vagal fibers are necessary for the effect. This has led to the hypothesis that the satiety effect is due to activation of vagal afferent fibers that inhibit the central control system of feeding by CCK acting directly on recently described vagal CCK receptors and/or indirectly through a gastric smooth muscle effect that vagal receptors are sensitive to.

Naltrexone and human eating behavior: a dose-ranging inpatient trial in moderately obese men.

To investigate the effects of the long-acting opiate antagonist naltrexone on spontaneous human eating behavior, eight moderately obese male paid volunteers were housed in a hospital metabolic unit for 28 days and offered palatable foods ad lib by a platter service method. Under double-blind conditions, equally divided doses of 100, 200 and 300 mg naltrexone, or an acetaminophen placebo, were administered twice daily in tablet form for 3-day periods each, according to a Latin Square design. The doses of naltrexone resulted in decreases of daily caloric intake from placebo level, but these reductions were neither statistically significant nor dose-related. When the averaged effects of the doses were compared to placebo, five subjects showed intake reductions but the overall intake reduction of 301.5 +/- 198.1 kcal/day (mean +/- SEM) was not statistically significant. Naltrexone administration failed to selectively alter intakes of individual meals and snacks or macronutrient consumption patterns. During active drug periods, subjects lost 0.62 +/- 0.22 lb over 3 days, while during the placebo period, subjects gained 0.46 +/- 0.68 lb. However, there was no reliable change of basal metabolic rate as a function of naltrexone administration. The present results, which indicate that naltrexone administration is relatively ineffective in reducing food intake and inducing body weight loss in obese humans, are thus in contrast with reports that administration of opiate antagonist agents promote significant reductions of food intake and attenuations of body weight gain in experimental animals.

The threshold for satiating effectiveness of psyllium in a nutrient base.

A combination of psyllium fiber with nutrients in a commercially available wafer (Fiberall-Ciba Consumer Pharmaceutical) was evaluated for its effectiveness in reducing food intake and appetite. Each of 15 nonobese healthy women received no wafers and four different amounts (39, 104, 169, and 234 kcal) of the fiber wafer with water, in a ratio of 13 kcal (and 0.565 g psyllium) wafer per 41.67 g water, 30 minutes prior to a test meal of macaroni and beef, on nonconsecutive days. Intake of the test meal and hunger ratings were both significantly reduced after intake of the two largest wafer amounts (169 and 234 kcal, respectively), in comparison with the two smaller amounts and none at all. The reduction produced by the largest amount compared to none at all was 122 kcal (about half the energy of the amount given). There were no significant differences in intake and hunger ratings among the two smaller amounts and none at all. Thus the threshold for intake reduction by this product with water lies between 104 and 169 kcal. Methodologically, this work underscores the importance of testing the satiating effects of foods at multiple levels before conclusions are drawn about their satiating effectiveness, and suggests that the threshold for significant reduction should be considered as a measure of the product's satiating effectiveness. The relative contributions of the nutrients, the fiber, and the water to the satiating effect still need to be determined.