Physiology & Behavior, Vol. 47, pp. 555-559. ©Pergamon Press plc, 1990. Printed in the U.S.A.

0031-9384/90 $3.00 + .00

Oral Stimulation With Aspartame Increases Hunger M I C H A E L G. T O R D O F F A N D A N N E T T E M. A L L E V A

Monell Chemical Senses Center, 3500 Market St., Philadelphia, PA 19104 R e c e i v e d 2 A u g u s t 1989

TORDOFF, M. G. AND A. M. ALLEVA. Oral stimulation with aspartame increases hunger. PHYSIOL BEHAV 47(3) 555-559, 1990.--We evaluated whether "sweetness" increases hunger. Groups of 10 male and 10 female subjects chewed a gum base containing one of four concentrations of aspartame (0.05%, 0.3%, 0.5%, or 1.0%) for 15 min. Relative to groups given nothing or unsweetened gum base to chew, groups given the sweetened gum bases increased hunger ratings, but not in a manner monotonically related to aspartame concentration. The most effective aspartame concentration to increase hunger was 0.3% for females and 0.5% for males. The highest aspartame concentrations had a time-dependent, biphasic effect on appetite, producing a transient decrease followed by a sustained increase in hunger ratings. Thus, the concentration of the sweetener, the sex of the subject and the time after chewing, were all important determinants of whether "sweetness" increased hunger. Sweetness

Cephalic-phase reflex

Sex differences

Appetite

THERE is mounting evidence that under some circumstances sweetness unaccompanied by calories (i.e., nonnutritive sweeteners) can increase the motivation to eat. Rats that drink saccharin solution or sham-drink sucrose solution increase short-term food intake (19-23). Humans that drink solutions sweetened with aspartame, saccharin, or Acesulfame-K increase hunger ratings (2,15). Food intake is reliably higher after subjects eat saccharinsweetened yogurt than unsweetened yogurt (3). Moreover, subjects eat more of a snack-food meal 90 rain after consuming a sweet milk shake than do subjects given the same milk shake preceded by treatment with gymnemic acid, an inhibitor of sweetness perception (5). There are also several reports where the effects of artificial sweeteners on the motivation to eat are not apparent. Nonnuwitive sweeteners given over long periods (>24 hr) rarely increase food intake or body weight [e.g., (7, 8, 11, 13, 14); but see (10, 16, 18)]. However, these studies do not directly address the question of whether sweetness increases appetite because any short-term effects of sweetness may be counteracted by long-term controls of intake. More pertinently, in short-term tests, no difference in food intake was seen after human subjects consumed aspartame- or sucrose-sweetened preloads mixed into milk shakes (5), Jell-O brand gelatin (17) or fruit-flavored beverages (1). Unfortunately, the studies using humans in this area suffer from a number of methodological problems [see (3,4) for reviews], three of which are relevant here. First, the control(s) required depends on the purpose of the study. To examine whether sweetness influences hunger, it is necessary to compare equicaloric sweet and unsweet stimuli, not nonnutritive and nutritive sweeteners. Second, all studies to date have used only one level of sweetness. Because this tends to differ from study to study, interlaboratory comparisons are difficult. Third, there has been no attempt to eliminate the postingestive effects of the sweeteners' vehicle. The importance of this is underscored by the f'mding that

rats increase food intake after they drink saccharin presented as a hypoosmotic but not hyperosmotic solution (21). Indeed, one difference between studies that do and do not demonstrate effects of sweetness on the motivation to eat is the vehicle used to deliver the nonnutritive sweetener. In the study presented here, we have attempted to rectify these problems by asking subjects to give subjective ratings of hunger at intervals after they chewed an unflavored gum base that was sweetened with one of five different concentrations of aspartame. The gum base was chewed but not swallowed, so the subjects received profuse oral stimulation with minimal postingestive effects. METHOD

Subjects Subjects were 60 males and 60 females who responded by telephone to advertisements posted on and around the campuses of the University of Pennsylvania and Drexel University. In the initial telephone interview, potential subjects were told they would receive $7.50 to chew gum and answer questions for 90 min. They were informed that they could not participate in the study if they had diabetes, hypoglycemia, or phenylketonuria. If the respondents remained interested an appointment was made for them to visit the laboratory. They were asked to eat their "normal breakfast" on the day they were tested and to abstain from eating or drinking for the 2 hr before testing, which occurred between 10:30 a.m. and 12:30 p.m.

Procedure Subjects were tested individually. When they first arrived at the laboratory they signed their consent to participate in the study. The consent form included brief instructions and reminders of the

555

556

TORDOFF AND ALLEVA TABLE 1

SWEETNESS

CHARACTERISTICS OF SUBJECTS

Characteristic Age (years) Height (cm) Weight (kg)

Female (n = 60)

Male (n = 60)

25.5 ___0.9 165.3 ± 0.9 61.0 - 1.8

26.1 ± 0.9 175.8 _.+ 1.0 69.6 ± 1.1

--10 --20

BITTERNESS

Note: values are means ± SE.

..

-)6

20

subject requirements (previously given by phone). Each subject's height and weight was measured (see Table 1) and they were asked about dietary habits, including when they had last eaten and how frequently they used chewing gum. Then, at 15-min intervals for 90 min, they completed a series of 10-cm visual analogue scales anchored with the descriptors "not very" and "extremely." Questions concerned the subjects' current motivational and emotional state ("How thirsty/hungry/tense/anxious/queasy are you? How good does your stomach feel? How sick do you feel?"), and the effects of the gum in the oral cavity ("How sweet/bitter/ intense/pleasant is the taste in your mouth?"). Except for the group of subjects that was given nothing to chew, all subjects were required to chew during the 15-min period between the first (prechewing baseline) and second series of analogue scales.

10 o

--10 .1~ - - 2 0

fr ¢_

INTENSITY

40 30 20 10 0

PLEASANTNESS

30

Design and Analysis

T

"1"

--10

20

Subjects were assigned at random to one of six groups, with 10 males and 10 females in each group. Subjects in one group received nothing to chew. In the other five they chewed a single piece (1150 mg) of gum base containing 0%, 0.05%, 0.3%, 0.5%, or 1.0% aspartame. To provide the simplest possible stimulus, the aspartame was mixed into a commercially prepared gum base that had no flavorants and no other source of sweetness (e.g., sucrose, sorbitol or mannitol). Pilot work suggested that the gum bases containing 0.3% and 0.5% aspartame were approximately as sweet as commercially available chewing gum. Significant effects in visual analogue ratings of each question were determined by three-way analyses of variance with betweensubject factors of Sex (female and male) and Group (nothing to chew, and the five concentrations of aspartame) and a withinsubject factor of time (0, 15, 30, 45, 60, 75, 90 min). If conventional levels of statistical significance were achieved (p

Oral stimulation with aspartame increases hunger.

We evaluated whether "sweetness" increases hunger. Groups of 10 male and 10 female subjects chewed a gum base containing one of four concentrations of...
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