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Keywords:

  • blindness;
  • eating behavior;
  • universal eating monitor;
  • vision

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Objective: Eating behavior is influenced by internal and external factors. Vision is one part of the complex pattern of factors influencing the amount of food consumed during a meal. The aim of this study was to explore the impact of vision on the microstructure of eating behavior and the subjective motivation to eat.

Research Methods and Procedures: Nine blind subjects and nine matched seeing control subjects consumed a standardized meal registered by VIKTOR, an eating monitor, measuring the microstructure of the eating behavior. The eating behavior of the control subjects was registered twice, with and without blindfold.

Results: The eating behavior of the blind subjects did not differ from that of seeing control subjects. However, the eating behavior of seeing subjects eating with blindfold demonstrated a clear impact of vision on eating behavior. When blindfolded, subjects ate 22% less food (p < 0.05), had shorter meal durations (p < 0.05), and had less decelerated eating curves (p < 0.05). Despite a smaller amount of food consumed when blindfolded, the reported feeling of fullness was identical to that reported after the larger meal consumed without blindfold.

Discussion: The importance of vision in regulating our eating behavior is further stressed in this study. Eating with a blindfold decreased the intake of food, without making subjects feel less full. Eating blindfolded, therefore, may force subjects to rely more on internal signals. These results might be used as an aid in the development of new treatment strategies for obese subjects.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Eating behavior is controlled by numerous factors, both internal physiological signals and external signals arising from cognitive cues, social factors, and cultural rules, as well as cues from the actual food eaten (1). Vision is one important component in this complex system regulating food intake. Obese subjects ate more cashew nuts if the light in the room was brightly illuminated compared with when the light in the room was dim (2). When four normal-weight men sipped lunch meals from a liquid food dispenser with the reservoir either hidden or visible, all subjects significantly decrease their intake when the food source was visible (3). However, neither liquid meals nor cashew nuts are the types of food usually eaten at normal meals and, thus, are not representative in reflecting the effect of vision on everyday eating behavior. Furthermore, the impact of vision on the microstructure of the eating behavior, such as the time of consumption and eating rate, has not previously been explored. The VIKTOR equipment, which measures the microstructure of eating behavior, has been found to be a useful tool for identifying differences in single-meal eating behavior between clinical groups (4, 5, 6, 7, 8), as well as in studies with within-subjects design to test the effects of manipulations on satiety (9, 10, 11, 12). Thus, we have analyzed the microstructure of the eating behavior and subjective motivation to eat in blind subjects compared with subjects with normal vision eating with and without blindfolds using the VIKTOR equipment.

Research Methods and Procedures

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Nine subjects, six women and three men, blind since birth or childhood (n = 8) or with no vision memories of food (n = 1), were recruited by an advertisement in the Swedish Braille magazine to participate. The subjects had no disabilities other than vision impairment and were taking no medications. A seeing control group matched for body mass, age, and gender (Table 1) was recruited from the hospital staff.

Table 1.  Clinical characteristics of blind subjects and controls*
 Blind subjectsControl groupStatistics
  • NS, not significant.

  • *

    Median and ranges are shown.

Age (years)49 (41 to 59)55 (40 to 58)NS
Body mass index (kg/m2)23.4 (21.2 to 34.6)25.0 (22.1 to 34.2)NS
Smoker (n)00NS
Blind since (year)0 (0 to 5) 

The microstructure of the eating behavior was measured by VIKTOR (Cabmek, Stockholm, Sweden), a universal eating monitor, previously validated and used in several studies (4, 5, 6, 7, 8, 9, 10, 11, 12). Briefly, the VIKTOR equipment consists of a table with a hidden scale connected to a computer that registers on-line graphically the total intake of food (in grams), the duration of consumption (minutes), the eating rate (grams/minute), and the rate of deceleration, defined as the reduction in eating rate that normally occurs toward the end of a meal. The eating curve is fitted to a polynomial, and twice the quadratic coefficient represents the rate of deceleration. A negative coefficient illustrates a decelerating eating curve and a positive coefficient illustrates an accelerating eating curve (Figure 1). The most common type of eating curve is the decelerated eating curve, which has also been called the “biological satiation curve” (13).

image

Figure 1. Typical VIKTOR eating curves.

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The subjective motivation to eat, defined as hunger, the desire to eat, fullness, and prospective consumption were measured by conventional analog rating scales (5, 14). Subjects rated how hungry, full, etc. they felt from 0 to 100, where 0 represents not at all and 100 represents very, very much. All subjects, seeing and blind, were asked to rate orally on non-visual scales.

Experimental Procedure

None of the subjects were informed about the details regarding eating behavior measurements on VIKTOR until after the study.

The information given before the study was that the effect of vision on “the experience of appetite and of eating” was to be studied. No mention of eating behavior measurements was given until after the last meal on VIKTOR.

All subjects were instructed to eat their breakfast according to ordinary habits and not to eat anything else between breakfast and lunch. All subjects were asked to maintain the same exercise habits before test days. All these requirements were checked in detail on arrival in the laboratory.

The blind subjects had the test-meal lunch on VIKTOR once and the control group twice, with and without blindfold. To prevent familiarity with the meal when eating blindfolded, all subjects were blindfolded on their first eating occasion on VIKTOR. The two occasions were separated by 7 days for men (n = 3) and the menopausal woman (n = 4). For premenopausal women (n = 2), the two occasions were separated by 4 weeks to take menstrual cycle effects on eating behavior into consideration. All subjects had the test meal on the VIKTOR equipment at the same hour they were supposed to have their ordinary lunch meal. They were served an excess portion (800 g frozen weight) of a microwave heated Swedish hash (150 kcal/100 g) consisting of diced meat, onions, and potatoes mixed and fried (Nestlé AB, Bjuv, Sweden) and a glass of water. They were instructed to eat as much as they wished of the meal and to drink the glass of water. Before and after the meals, the subjects rated their subjective motivation to eat with analog rating scales (see above).

Data Analysis

Because the eating data were not normally distributed in all groups, statistical analyses of the eating data and the rating scales were carried out by using nonparametric statistics. Mann–Whitney U tests and Wilcoxon's signed ranks test were used for unpaired and paired comparisons, respectively. When comparing the number of decelerated eating curves in each group, Fisher's exact test was used. A value of p < 0.05 was considered statistically significant. Approval of the study was obtained by the local ethics committee and all subjects gave their informed consent to participate.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

There were no significant differences in eating behavior regarding duration of consumption, total intake of food, and degree of deceleration, when blind and seeing subjects were compared (Table 2), nor were there any significant differences between the two groups in subjective motivation to eat before or after the meal.

Table 2.  Eating behavior characteristics of blind and control subjects with and without blindfold*
  Control group 
 Blind subjectsBlindfoldedWithout blindfoldStatistics
  • *

    Medians and ranges are shown.

  • p < 0.05 within control group.

  • p < 0.05 between blind and controls without blindfold.

Total intake of food (g)281 (195 to 717)248 (117 to 317)316 (190 to 440)
Time of consumption (min)8.9 (6.8 to 27.8)6.5 (4.8 to 10.4)7.0 (4.6 to 10.3)
Eating rate (g/min)30 (21 to 53)39 (21 to 59)39 (28 to 77)
Deceleration (g/min2)−1.5 (−4.1 to 1.7)−0.5 (−4.2 to 3.0)−1.2 (−3.5 to 1.5)

When blindfolded, the seeing control group ate less (Z = −2.55, df(8), p < 0.05) than without the blindfold. The eating rate, however, was the same with and without blindfold, so the duration of the meal was shorter in the blindfold state (Z = −2.07, df(8), p < 0.05). The eating curves decelerated less toward the end of the meal when eating with the blindfold (Z = −2.19, df(8), p < 0.05;Table 2). Four of nine subjects exhibited decelerated eating curves when eating blindfolded, whereas seven of nine subjects had decelerated eating curves when not blindfolded. Most interestingly, there were no significant differences in the ratings of motivation to eat, either before or after the meal, when the two experimental situations were compared. None of the subjects experienced that it was technically more complicated to eat blindfolded, which was objectively verified by the lack of spilling or dropping of food in the laboratory setting.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

This study reveals that vision is of fundamental importance in regulating our eating behavior. Vision not only influences the microstructure of the eating behavior, but also the subjective feelings of satisfaction after the meal. When control subjects had their test meal blindfolded, their subjective ratings of fullness after the meal were similar to the ratings obtained after the meal without blindfold, despite a 22% significantly decreased caloric intake.

The rate of deceleration was also affected; when eating blindfolded, the eating curves were less decelerating compared with eating without a blindfold. A less decelerated eating curve could possibly indicate an arrest in eating before fullness, but because the subjective feelings of fullness were identical that could not be a plausible explanation.

An explanation to the reduction in intake could be the phenomenon of “sensory-specific satiety.” Sensory-specific satiety refers to an enhancement of food intake when a variety of foods with different sensory and nutritional properties are served, compared with a situation with only one or a few food components (15). Sensory-specific satiety also occurs for the visual appearance of food, such as shape and color. For example, when pasta with three different shapes was served, subjects ate 14% more compared with when they were offered their favorite shape throughout (16). The question is whether the specificity of satiety extends to the visual modality, such as vision vs. no vision at all.

Perhaps vision does contribute to estimation of the satiating potential of foods. When we see familiar food, we have some experience of how satisfying it will be and will make a judgment about how it will satisfy us by designing our meal plan. Without vision, the meal plan of the sighted food is lost and one element of within-meal satiation is absent. Vision may stimulate but also contribute to satiety cognitions that terminate intake.

The hypothetical explanation for the decreased food intake while eating blindfolded could also be a normal variability of the eating behavior. However, this is not likely, because data on the reproducibility of VIKTOR measurements have shown that variables such as eating rate and amount of food eaten are stable, if physical habits and eating patterns are controlled before test meals (5). In this study control subjects were asked to maintain breakfast and exercise habits before test meals and menstrual cycle effects on eating were also controlled.

A number of internal factors contribute to the termination of eating, such as gastric distension and release of intestinal peptides affecting neural mechanisms (17). External factors such as vision may also affect neural mechanisms in the brain involved in the termination of eating. The cephalic phase of digestion in response to the sight and smell of food eliciting salivation, insulin release, and gastric acid secretion is a well-known phenomenon (18). The removal of sight, therefore, may influence the cephalic phase, which, in turn, can affect satiation (the willingness to stop eating) and also the feeling of fullness after the termination of the meal. The details in such modulation, however, are so far unknown.

Vision has an impact on eating behavior among subjects who are full-sighted, but obviously not among subjects blind since birth. The blind subjects have probably adapted and are to a greater extent using internal signals to determine how much to eat. If seeing subjects become blind, they would probably adapt and learn to rely on other senses than vision such as internal signals. It is unclear how long this adaptation takes.

Despite the small number of subjects in this study, the differences between the experimental situations revealed an important regulatory impact of vision, which needs further explanations. An issue of importance, for example, is whether the subjects compensated for the decrease in the amount of food eaten at the lunch meal by eating more in the afternoon or in the evening.

In summary, in this study, the importance of visual signals to regulate food intake was demonstrated. Eating blindfolded decreased the intake of food, without making subjects feel less full. Manipulation of the visual cues of a meal might be used for more detailed studies on eating behavior and may provide interesting new approaches in the treatment of obesity.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

This study was supported by the Stockholm County Council Resource Centre for Eating Disorders.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
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