Abstract:
Human satiety and hunger are usually measured by observations of
eating behavior or by verbal reports. Neither of these seems to be an
objective method of measurement. Some studies have indicated that pupil
responses to pictures of food may correspond with interest in food. The
objective of this study was to determine the feasibility of using pupil
responses to food pictures to measure human satiety.
Pupil sizes of 17 women, mean age 25.3 years, were measured as the
women watched slide pictures of food before and after eating a high
carbohydrate breakfast. Each subject participated in one to four experiments.
Plasma glucose values were measured with the AutoAnalyzer
ferricyanide method. Samples were taken during the fasting state and
at approximately 30, 45, and 60 minutes after a breakfast which contained
one gram of carbohydrate per kilogram of subject's body weight.
Pupil sizes were measured with equipment which included an infra-red
sensitive television camera. Pupil responses to pictures of food were
compared to pupil responses to control pictures of non-food items. The
differences of the changes in pupil responses before and about 50 minutes
after eating were compared to several variables to determine correlation
coefficients.
Plasma glucose values were found to be similar to those in other
studies in which subjects ingested glucose solutions. Fasting glucose values were similar for all subjects using oral contraceptives and those who were not. Samples taken at approximately 60 minutes showed
a higher plasma glucose level (118.6 mg./100 ml. [plus or minus] 30.7) for oral
contraceptive users than for non-users (95.2 mg./100 ml. [plus or minus] 15.4).
Several significant correlations were found between changes in
pupil response to food pictures after eating and some of the considered
variables. Blue-eyed subjects had increased pupil responses to pictures
of peaches and crackers, and brown-eyed subjects had decreased responses
to these pictures (peaches, p<.05; crackers, p<02). Subjects who
usually ate all they wanted had increased responses to pictures of
crackers, and subjects who restrained their eating had decreased responses to these pictures (p<.02). Increasing rate of the fall in plasma
glucose correlated with smaller or negative changes in response to
pictures of eggs and sausage, cookies, and jelly on toast. Decreasing
rapidity of the plasma glucose fall was associated with greater responses to these pictures (eggs and sausage, p<.05; cookies, p<.02;
jelly on toast, p<.05).
Other significant correlations were also found for changes in pupil
responses to various food pictures when the variables of time of day,
experiment number, body mass index and percentage of body fat (as determined
by skinfold measurements) were considered, but there is some doubt
about the validity of these correlations. No correlations were significant
when comparisons were made of pupil response changes and the variables
of oral contraceptive use, age, plasma glucose value, days before
menses, and the time after eating.
Suggestions are given for improvements in the experimental method.
The significant correlations of pupil response changes with the rate of
plasma glucose decline are in agreement with other reports of significant
correlations between verbal ratings of hunger and satiety and
capillary-venous differences in blood glucose. With some modifications
in techniques, it is suggested that further studies of human satiety
and hunger involve pupillometry.
