1. Does slowing the rate of access to a highly palatable food lead to reduced food consumption in laboratory rats? Travis Boyd, Brandon Hunt, Kelsi Koenig and G.R. Davis Department of Biology, Wofford College, Spartanburg, SC
Introduction
Major Findings
Phase I: Determining Baseline Eating Speed
It has been speculated that reducing the rate of food intake will lead to a reduction in overall food consumption by allowing satiety signals to accumulate to levels that lead to an earlier termination of the meal (Stuart, 1967). If this is the case, then eating slowly may be an effective strategy for weight management. Martin et al. (2007) reported that reducing the rate of food consumption resulted in reduced food intake in men but not women. Rats regulate their intake based on a caloric “goal” regardless of meal duration or experimental interruptions when administered a glucose solution at a constant rate (Seeley et al., 1993). However, the mechanisms underlying the termination of a meal may differ for meals consisting of liquid or solids. Our purpose here is to determine whether reducing the rate of food consumption in hungry male Sprague-Dawley rats will result in reduced intake of a highly palatable solid food.
Reducing the rate of Froot Loop intake did not result in reduced Fruit Loop consumption.
Average meal duration doubled or quadrupled when rate of consumption was restricted to one-half and one-fourth of baseline rate, respectively. Rats appear to be adjusting their meal duration to achieve a caloric intake goal. 1 2
Status of Hypothesis
Reducing the rate of eating did not affect total Froot Loop intake. In other words, eating more slowly did not affect the amount of food eaten.
Figure 1: By Unrestricted Trial 3 (UT 3), Froot Loop intake had stabilized at ~9.5 grams. Figure 2: By Unrestricted Trial 2, the rate of intake had stabilized such that rats required approximately 35 seconds to eat a Froot Loop. Rats acclimated to the experimental protocol and overcame neophobicity within the first three weeks (trials) of Phase I.
Statistics for Phase I and II: Repeated Measures ANOVA followed by post hoc pair-wise testing (Student-Newman-Keuls, p <0.05)
Hypothesis
Discussion
Reducing the rate of food consumption will result in decreased food intake in laboratory rats.
These results show that reducing eating speed is not effective as a strategy to reduce intake of a carbohydrate-rich food in hungry non-naïve male laboratory rats. These results differ from that reported by Martin et al., 2007 who showed that human males consume less fried chicken when their rate of intake was experimentally reduced. Mechanisms responsible for satiation may vary depending on the sensory properties and/or macronutrient content of foods. Therefore, future experiments may explore the effects of slowing the rate of intake of protein-rich or fat-rich foods in laboratory rats.
Our protocol is similar to that used by Seeley et al.(1993) who introduced pauses during a meal of intra-orally infused glucose solution in rats. Our results and conclusions are similar to Seeley et al.; rats compensate for meal interruptions by increasing meal duration in order to keep total intake relatively constant.
Since the present study was conducted on older male rats previously used for other purposes, it will be important to replicate these results in young naïve rats.
Future experiments might also investigate the effects of 1) altering food intake rate in non-food deprived rats, and 2) varying the types foods consumed during a meal in food-derived and non-food deprived rats.
Overview of Experiments
Phase I: Determine the baseline (unrestricted) rate of intake.
Phase II. Test hypothesis by reducing (restricting) the rate of intake to one-half or one-quarter of the baseline rate.
Phase II: Restricted Feeding
Methods
Having established the baseline (unrestricted) rate of Froot Loop intake as one FL every 35 seconds in Phase I, the hypothesis was tested by restricting the rate of intake to one FL every 60 seconds (R 1/2) or 1 FL every 120 seconds (R 1/4).
Following a standard 24 hour food deprivation, Froot Loops were inserted into the cage through the lid at 60 second intervals or 120 second intervals (4 rats per observer). Observers recorded the time required to consume each FL to the nearest second. As before, the meal was considered terminated if the rat refrained from the Froot Loop for 10 min. Meal duration, grams consumed, the number consumed, and time to consume each Froot Loop was recorded for all 20 subjects. This experiment was counterbalanced by having each rat restricted at both rates separated by two weeks.
Twenty male Sprague-Dawley rats previously used for other purposes (Mackechnie et al., 2008 and Govind et al., 2008) were used in this pilot study. Rats were ~6 months old and weighed 588 ± 51 grams at the onset of this experiment.
Rats were housed individually in plastic cages with bedding and provided ad libitum rat chow (Harlan Teklad 8604) and water.
Rats were maintained on a 12:12 hour light dark schedule (lights on at 8 AM).
Phase I: Establishing the Baseline Rate of Eating
After a 24 hour food deprivation once per week, rats were weighed and returned to their cages without bedding. At time zero (approximately 9 AM, one hour into the light period) a Froot Loop® was inserted into the cage through the lid and an observer recorded the time with a stopwatch. Once that Froot Loop had been consumed, the time to consume the Froot Loop was recorded to the nearest second and another Froot Loop was immediately inserted into the cage. This process was repeated until the rat failed to consume a Fruit Loop for 10 min at which time the meal was considered terminated. Meal duration (time at which the last FL was eaten), number of Froot Loops eaten, grams of Froot Loops consumed, and time to consume each Froot Loop was recorded for all 20 rats. Rate of intake was calculated as # FL consumed/meal duration. Five observers recorded data for each of four rats during each trial. Trials were repeated weekly until the baseline (unrestricted) rate of intake had stabilized.
In an additional trail , 24-hr food-deprived rats were provided ad libitum access to a pre-weighed bowl of FL inserted into the cage to assess whether the mode of FL delivery affected intake or rate of intake. 3 4
References
Figure 3: Grams of FL consumed did not differ significantly between restricted and unrestricted trials except for Unrestricted Trial 1 as rats acclimated to the protocol. Figure 4: When rate of intake was reduced by ½, meal duration doubled. When rate of intake was reduced by ¼, meal duration quadrupled.
Neither FL intake (Figure 3) nor meal duration (Figure 4) was affected by the mode of FL delivery (individually or ad libitum from a bowl; UT (Bowl)).
Seeley et al., 1993 Appetite 20:13-20.
Martin et al., 2007 Behav. Res. Therapy 45:
Mackechnie et al., 2008 Southeastern Bio. in press. Govind et al., Southeastern Bio. in press.
Acknowledgements
Time to consume each FL Condition (mean ± SEM) Unrestricted Trial 4: ± 2 sec R (1/2): 28 ± 1 sec* R (1/4): 32 ± 1 sec
Our protocol did not actually reduce eating speed. Surprisingly, rats restricted to one-half their baseline eating speed actually consumed FL at a slightly faster rate.
The authors are indebted to Nicole Woller and Kelly Berry who assisted with data collection and animal care. This project was funded by a Community of Scholars grant from the Fullerton Foundation to Wofford College.