Responses of lean and obese subjects to preloads, deprivation, and palatability.

The effects of preloads, deprivation, and palatability on the eating behavior of non-dieting lean and obese subjects were studied during laboratory meals, using small solid food units (SFUs) to measure the rate of ingestion over the time-course of the meals. In both weight groups, rate of intake decreased from the beginning to the end of meals. The smaller the preloads and the longer the deprivation interval, the faster subjects ate at the beginning of meals and the higher their hunger ratings were. The longest deprivation interval also increased palatability ratings, meal length, and the total amount that subjects ate. Increasing the palatability of the food increased the rate of intake at the beginning of meals, meal length, and the amount of food that subjects ate. Obese subjects were more sensitive to palatability and less responsive to deprivation than lean subjects. For example, while lean subjects became less discriminating about the palatability of the food at the beginning of meals as deprivation increased, obese subjects did not. The satiation mechanism of obese subjects was also different from lean subjects. For example, obese subjects overate after preloads while lean subjects underate compared to their baselines.

Sugar and fat: sensory and hedonic evaluation of liquid and solid foods.

Twenty-five subjects evaluated the sweetness, creaminess and fat content of liquid and solid dairy products containing between 0.1 and 52 g fat/100 g and sweetened with 0-20% sucrose weight/weight. Liquid stimuli included skim milk, whole milk, half and half, and heavy cream, while the solids included cottage cheese and cream cheese, blended and spread "jelly-roll" fashion on slices of white bread. The subjects' ratings of stimulus sweetness, creaminess, and fat content differed sharply between liquids and solids, and the assessment of fat content of solid foods appeared to be impaired. In contrast, acceptability ratings for both sets of stimuli were not substantially different: the subjects optimally preferred equivalent levels of sugar in both liquids and solids, but selected higher fat levels in solid than in liquid foods. Sensory preferences for fat in liquid stimuli may not always be indicative of preferences for fat in solid foods.

Effect of naltrexone on food intake, hunger, and satiety in obese men.

Increasing doses of naltrexone (25 to 200 mg) given over 4 consecutive days reduced intake of laboratory luncheon meals by 30% in 17 obese men. Meal size remained suppressed in the laboratory during the week following naltrexone administration. Water intake in the laboratory and body weight were not affected. Rates of ingestion and subjective ratings suggested that naltrexone reduced appetite rather than promoted early satiation. Nausea and other side effects occurred on 1 or 2 days during the naltrexone week in seven subjects whose food intake was reduced. Food intake was also reduced in seven of the remaining 10 subjects who reported no adverse reactions. These results suggest that a conditioned taste aversion or a conditioned anorexia may have developed in some subjects.

The effects of repeated cycles of weight loss and regain in rats.

This study examined the metabolic effects of weight cycling, i.e., repeated periods of weight loss followed by regain. There were three groups of adult, male Sprague-Dawley rats: (1) Chow Controls (a normal weight control group fed chow throughout); (2) Obese Controls (animals fed a high-fat diet throughout); and (3) Obese Cycling (obese animals cycled through two bouts of caloric restriction and refeeding). The cycled animals showed significant increases in food efficiency (weight gain/kcal food intake) in the second restriction and refeeding periods compared to the first, i.e., weight loss occurred at half the rate and regain at three times the rate in the second cycle. Several physiological changes were associated with this cycling effect. At the end of the experiment, cycled animals had a four-fold increase in food efficiency compared to obese animals of the same weight who had not cycled. These data suggest that frequent dieting may make subsequent weight loss more difficult. The possible metabolic and health consequences of "yo-yo" dieting are discussed.

Chews and swallows and the microstructure of eating.

The study of eating behavior in animals and humans shows that much is learned if detailed and sensitive measurement of the ingestive process can be made. It is possible to measure all chews and swallows of human subjects during a meal. This proves to be a sensitive way to measure the microstructure of a meal, reflecting hunger, palatability, and satiation. The oral sensor promises to be an unobtrusive and objective method of measuring all meals, snacks, and nibbling throughout the day. The oral sensor should provide a means of evaluating both the palatability and the satiating value of foods and the role of hunger and other manipulations of the internal environment in changing the chewing and swallowing microstructure of eating.