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.

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.

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.

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.

Impact of medium and long chain triglycerides consumption on appetite and food intake in overweight men.

BACKGROUND: Medium chain triglycerides (MCT) enhance thermogenesis and may reduce food intake relative to long chain triglycerides (LCT). The goal of this study was to establish the effects of MCT on appetite and food intake and determine whether differences were due to differences in hormone concentrations. METHODS: Two randomized, crossover studies were conducted in which overweight men consumed 20 g of MCT or corn oil (LCT) at breakfast. Blood samples were obtained over 3 h. In Study 1 (n=10), an ad lib lunch was served after 3 h. In Study 2 (n=7), a preload containing 10 g of test oil was given at 3 h and lunch was served 1 h later. Linear mixed model analyses were performed to determine the effects of MCT and LCT oil on change in hormones and metabolites from fasting, adjusting for body weight. Correlations were computed between differences in hormones just before the test meals and differences in intakes after the two oils for Study 1 only. RESULTS: Food intake at the lunch test meal after the MCT preload (Study 2) was (mean±s.e.m.) 532±389 kcal vs 804±486 kcal after LCT (P<0.05). MCT consumption resulted in a lower rise in triglycerides (P=0.014) and glucose (P=0.066) and a higher rise in peptide YY (PYY, P=0.017) and leptin (P=0.036) compared with LCT (combined data). Correlations between differences in hormone levels (glucagon-like peptide (GLP-1), PYY) and differences in food intake were in the opposite direction to expectations. CONCLUSIONS: MCT consumption reduced food intake acutely but this does not seem to be mediated by changes in GLP-1, PYY and insulin.

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.

Metabolic correlates of eating behavior in severe obesity.

BACKGROUND: The benefit of spreading energy intake over many small meals ('nibbling') rather than few large ones ('gorging') for control of blood glucose, serum lipids and body fat accretion has been known for 60 y, but the mechanisms are poorly understood. Men exhibit more of a gorging eating pattern than women and are also more prone to the metabolic complications of obesity, as are women with a 'male', central distribution of adipose tissue. We have shown correlations between central fat distribution, and other components of the metabolic 'Syndrome X' and fatty infiltration of the liver. Here we study relationships between eating rate and fat distribution and test the hypothesis that gorging might be associated with fatty liver. SUBJECTS AND METHODS: In 30 non-alcoholic, non-diabetic, severely obese women (body mass index, BMI=47+/-1 kg/m(2); mean+/-s.e.m.) with a mean age of 36+/-1 y and 16 men (BMI: 52+/-3) age 38+/-2 y, who were candidates for anti-obesity surgery, we measured eating rate using an eating monitor, and fat distribution by the waist-hip circumference ratio (WHR). In addition in the 17 women and 11 men who had surgery, serum lipids were analyzed and routine liver biopsies were evaluated for steatosis by a pathologist blinded to the conditions of the study. RESULTS: Men ate significantly faster than women (188+/-28 vs 123+/-9 g/min; P<0.01), and had more liver fat (score: 2.7+/-03 vs 1.5+/-0.3; P<0.01), with no statistically significant sex differences in s-cholesterol or s-triglycerides. Eating rate correlated with WHR (r=0.46; P<0.01, n=46), liver fat (r=0.55; P<0.01), and s-triglycerides (r=0.42; P<0.05) adjusting for sex. Liver fat correlated with WHR (r=0.50; P<0.05), s-triglycerides (r=0.70; P<0.01) and s-cholesterol (r=0.50; P<0.05), while there were no significant correlations with BMI or body weight. In multivariate analysis eating rate (32%), meal size (8%) and WHR (6%) contributed 46% of the variance in liver fat. CONCLUSION: We showed increased eating rates in severely obese men and women with central fat distribution. Furthermore, increased eating rates were associated with fatty liver and elevated serum lipids. Eating rate in severely obese women and men may be a determinant of the metabolic syndrome.

PROP taster status and oral fatty acid perception.

Recent studies with rat taste cells treated with polyunsaturated fatty acids suggest that fatty acids may play a role in dietary fat perception. In humans, sensitivity to the textural properties of fat is associated with the genetic ability to taste the bitter compound 6-N-2-propylthiouracil (PROP). However, it has not been shown that PROP tasters are more sensitive in discriminating fatty acids in a high-fat food. Our study with human subjects was designed to test the hypothesis that the ability to orally detect food-grade conjugated linoleic acid added to high-fat vanilla ice cream is associated with the ability to taste PROP. Eighty percent of the PROP tasters in this study, but only 17% of the PROP nontasters correctly discriminated the sample containing the added free fatty acid in a difference test versus unadulterated high-fat vanilla ice cream (Fisher's Exact Test, P=.05). Because most fatty foods contain minute amounts of free fatty acids, further studies with humans examining the contribution of fatty acids to fat perception seem warranted.

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.

Patterns of food selection during binges in women with binge eating disorder.

OBJECTIVE: The aim of this study was to determine whether temporal patterns of food selection during binges in obese subjects with binge eating disorder (BED) differ from those of patients with bulimia nervosa (BN). METHOD: Ten obese women with BED and 10 weight-matched women without BED each consumed a multiple-item meal identical to that used in previous studies with bulimics, and all subjects were instructed to binge. An experimenter recorded the subjects' food choices every 10 s throughout the meal via a closed-circuit TV camera. RESULTS: Subjects with BED consumed significantly more meat than subjects without BED (397.78 vs. 270.64 kcal), but the food choices and percentages of time spent eating each of the foods were similar among BED, non-BED, and normal weight controls. While bulimics ate dessert foods earlier in the meals, all other groups ate meat towards the beginning of their meal and ate more dessert foods towards the end of the meal. DISCUSSION: Food selection patterns during binges in subjects with BED are more similar to eating patterns of noneating disordered subjects, than to patterns seen in patients with BN. These data suggest that binge episodes between different groups of eating-disordered populations are qualitatively different.

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.

A direct measure of satiety disturbance in patients with bulimia nervosa.

To determine whether patients with bulimia nervosa (BN) experience the development of satiety during a meal differently than control subjects, a novel laboratory meal procedure was employed. Eleven women with BN and 11 women without eating disorders consumed a yogurt shake meal after being instructed to binge. After each 75-g increment consumed, the subjects were signaled by a tone to fill out a questionnaire on which they were asked to rate various sensations on visual analog scales. The sensations included "Fullness", "Hunger", "Desire" for a favorite food, "Pleasantness" of consuming the shake, "Sickness", and having "Enough" to consume. Although patients, before purging, consumed significantly more food than the controls, who did not purge (1597 +/- 626.5 g vs. 1004 +/- 362.5 g, mean +/- SD), their final questionnaire ratings were not significantly different from the controls' ratings. Patients ate significantly more than the controls before reaching 50% of their range of "Hunger" rating and 75% of their "Full", "Desire", "Sick", and "Enough" rating ranges. The patients also ate significantly more than the controls between 75% and 100% of their "Hunger" rating range. These data suggest that one possible mechanism for overeating in patients with BN may be their failure to perceive or respond as normal subjects do to the range of sensations associated with satiety. Collecting ratings as a function of intake may provide a method for assessing and studying eating disturbances in clinical populations.

The effect of social setting on response to a preloading manipulation in non-obese women and men.

To determine the effect of a social setting on the physiological controls of eating, four pairs of subjects consumed a 15% and a 1% glucose (sweetened with aspartame to match the 15%) preload drink, preceding a test lunch meal, individually in a laboratory, and as a pair in a cafeteria. Compared with the 1% glucose preload, the 15% glucose preload significantly reduced food intake by the same amount in both settings (mean meal intakes: 467.4 g vs. 610.2 g, respectively). Intakes were 141.3 g +/- 41.8 SED less after the 15% than the 1% preload in the laboratory setting (t28df = 3.38, p = 0.0022), and 144.2 g +/- 41.8 SED in the cafeteria setting (t28df = 3.45, p = 0.0018). This result suggests that different social settings do not significantly alter physiological satiety cues and demonstrates that at least one of the physiological controls of eating, that has been tested in a laboratory setting, is reproducible in a cafeteria setting.

Subjective ratings as a function of amount consumed: a preliminary report.

A new technique has been developed to study the changes in feelings of satiety during food consumption. Five non obese women were interrupted after eating 75 g increments of a tomato soup test meal served on an eating monitor to complete rating scales of hunger, satiety, fullness, sickness, and pleasantness of the meal. They were instructed to eat as much as they could, and their intakes ranged from 590 to 1288 g. The measured responses to each question were then plotted against the corresponding intakes. The slopes of the linear portions (in mm/g on 150 mm scales) were -.22 for hunger, -.21 for pleasantness of the food, and .27 for both fullness and satiety. The slope of the relationship between satiety and intake or the difference in intake between 25% and 75% of the maximum satiety response range could be useful measures for assessing either disturbances in satiety in clinical populations, or assessing relative satiating potencies of foods or beverages.

Effects of glucose and fructose solutions on food intake and gastric emptying in nonobese women.

The differential effects of fructose and glucose on food intake were studied by giving two concentrations (1 and 10%) of glucose and fructose solutions (500 ml) to one group of women 30 min, and to another 135 min, before a meal of macaroni and beef. The 1% solutions of each sugar were sweetened to match 10% fructose by selective additions of aspartame. Gastric emptying of the 10% solutions and water was measured for 90 min. Under the 30-min delay, subjects ate a mean of 75.8 g more (P < 0.05) after the 1% solutions than after water, and 52.2 g (P > 0.05) less after the 10% solutions than after water, but there were no differences in intake between types of sugar under either delay nor between concentrations at the 135-min delay. However, 10% fructose and 1% glucose sweetened to match it reduced intake significantly compared with water. Glucose (10%) emptied significantly slower (t1/2 = 93.61 min) than water (t1/2 = 29.77 min), while fructose (10%) was intermediate (t1/2 = 65.45 min). Therefore, gastric emptying differences did not account for these results. We conclude that sweetener-enhanced dilute sugar solutions may increase subsequent intake at 30 min, but dilute glucose solutions may have potential for substantial energy savings if consumed 135 min before a meal.

Eating behavior in binge eating disorder.

In order to examine the eating behavior of individuals with the newly proposed diagnosis, binge eating disorder (BED), standardized meals were served to 20 obese women, 10 with BED and 10 without BED. When asked to binge eat from a multiple-item array of foods, obese subjects with BED consumed significantly more calories than did obese subjects without BED. Significant differences between the two groups were also found on several of the self-report measures.