Does the rate of food intake
affect meal size?

Research Team: Kelsi Koenig, Kelly Berry,
Nicole Woller, Travis Boyd, Brandon Hunt, and
Dr.G.R. Davis (faculty sponsor)

Extension of Community of Scholars Summer 2007
into Fall 2007 Semeseter
Funding by the Fullerton Foundation

Results in Poster Format

last updated 25 April 2008

Common adage:

The faster you eat, the more you can eat before getting full.


The rate at which a person (or rat) eats may influence when the meal ends and how much is consumed. For example, stretch of the stomach is known to suppress additional food intake. Likewise, satiety signals that arise with the intake and digestion of a meal will terminate the meal. Here we are interested in determining whether the adage is true, but we turn to an animal model in which it is possible to control the state of hunger (by the duration of food deprivation) and, more importantly, control the rate at which the animals can consume a highly palatable food. Our intent is to determine the natural rate at which hungry rats consume Froot Loops. Once this information is obtained, we then intend to feed rats at a rate that is half or one-fourth as fast as their natural (unrestricted) rate. For this study we will measure the duration of the meal, the number and grams of Froot Loops consumed, and the time to consume each Froot Loop.

The Hypothesis:

Reducing the rate of consumption will result in a lower total intake of Froot Loops.

Restated Hypothesis:

Limiting the rate of food intake reduces the total food intake of a meal in laboratory rats.


Eating slower causes one to eat less.


Experimental Design:

We anticipate the study to consist of two sets of experiments, each consisting of four trails. During the first set of experiments, we will measure the unrestricted rate of food intake, the total food intake, and meal duration for each of 20 rats in four trials. During the second set of experiments, the rate of food consumption will be restricted to half or one-fourth of the unrestricted rate and again the total food intake and meal duration will be record for each rat over four trials.

Unrestricted Intake Experiments:

These pilot studies are designed to measure how quickly hungry rats consume Froot Loops. Thus we are measuring the unrestricted rate of consumption. Twenty adult male Sprague-Dawley rats maintained on ad libitum commercial chow (Teklad 8604) and water in individual plastic cages on a 12:12 hr light dark cycle (lights on at 9 am). Once per week rats were deprived of food for 24 hours beginning at 10 am. On the day of the experiment, rats were weighed and returned to their own cages with bedding removed. At time zero, a Froot Loop was inserted through the cage lid. When the rat had completely consumed the Froot Loop, the time to the nearest second was recorded and another Froot Loop was immediately inserted. This process was repeated until the rat failed to eat a Froot Loop after 10 minutes. In other words, if the rat did not consume the last Froot Loop within 10 minutes, the meal was considered ended. Meal duration, the total number and mass of Froot Loops consumed, and the time to consume each Froot Loop was recorded for each of 20 rats for 4 trials separated by one week.

A control unrestricted intake experiment was conducted on 1 November 2007 after 24 hr food deprivation as usual. For this experiment, a pre-weighed metal bowl containing FL was placed in each cage and rats consumed FL ad libitum until the conclusion of the meal (defined as a cessation of eating for 10 minutes, our standard for deterimining meal duration.) These data allow us to compare whether the meal duration, rate of intake, number of FL consumed, and grams of FL consumed is affected by the mode of access to FL (en mass in a bowl vs. singly through the cage lid.)


Results from Unrestricted Experiments used to establish the conditions of the Restricted Intake Experiments

By Trial 3, rats were consuming FL at an average rate of one FL per 35.3 ±2.1 seconds. By Trial 4, rats were consuming Froot Loops at an average rate of one FL per 35.0 ± 2.3 seconds. Therefore, for restricted intake experiments, we adjusted the rate of delivery to one FL every 60 seconds for 10 rats and one FL every 120 seconds for the remaining 10 rats. Thus, FL were provided during the restricted intake experiments at rates approximately one-half and one-fourth of the unrestricted rate. The experiment began after a 24 hour food deprivation. A stopwatch was displayed within view of all five observers, each of which conducted the experiment on four rats, with two rats receiving FL at 60 second intervals and the other two rats recieving FL at 120 second intervals. A sixth person monitored the time and announced to the observers 5 seconds before the next time at which FL were to be inserted into the cage lid via the opening for the water bottle. For each rat, the time to consume each FL, the number of FL consumed, the grams of FL consumed, and the meal duration in seconds was measured. As in unrestricted intake experiments, a meal was considered terminated when a rat had not consumed a FL in 10 minutes.The experiment was counterbalanced; each rat was fed at both restricted rates separated by two weeks. In the intervening week, an unrestricted access control experiment was conducted in which all rats were allowed to eat to satiety from a bowl placed in their cages.



The data summarized in the table below (collected over 7 weeks) clearly shows that reducing the rate of intake to half or one-fourth of the natural rate of eating does not affect the total intake of Froot Loops. Regardless of the rate at which rats are permitted to consume Froot Loops, they consume a fixed amount (approximately 10.5 grams or about 57 Froot Loops) by eating for twice or four times the standard meal duration.


Our results do not support the commonly held notion that "Slowing down causes you to eat less." That saying remains to be tested in humans but our data clearly dispels that notion for rats.


Future Experiments

Of course, there are many differences between feeding behaviors in rats and humans, and in some ways rats are not appropriate models for investigating human behaviors. However, rats provide remarkable experimental advantages from which much can be learned.

From this point, the research can proceed in several directions:

A) Our rats were food deprived for 24 hours prior to experimentation to intentionally make them hungry. We are considering repeating these experiments on non-food deprived rats to simulate the human situation of snacking on highly palatable foods even though not hungry. It is this non-hunger driven intake of food between meals that contributes to the overeating and obesity problems in industrialized nations. Perhaps the results we'd seen would be different in rats that were not driven to eat by a modest period of food deprivation.

B) Froot Loops are 84% carbohydrates. Perhaps the satiety mechanisms responsible for the termination of a high carbohydrate meal are different from those activated during a meal consisting of mainly protein or fat. Thus, we propose to replicated this experiment using peanuts which are rich in both fats and proteins. It may be that eating slower causes one to eat less if one is consuming fat and/or protein.




Trial 1
Trial 2
Trial 3
Trial 4

Restricted (60s)

Restricted (120s)

FL in bowl
Trial 5
rat body mass (g)
588 ± 51
590 ± 56
600 ± 55
600 ± 55
625± 55
628± 64
635 ± 60
641 ± 61
meal duration (s)
1230 ± 385
1533 ±391
1516 ± 391
1643 ± 350
3236 ± 927
6979 ± 1268
1823 ± 416
1633 ± 505
# FL eaten
28 ± 13
43 ± 14
45 ± 14
49 ± 13
55 ± 14
59 ± 11
48 ± 11 (calc)
47 ± 16
g FL eaten
6.0 ± 2.9
9.1 ± 3.0
9.5 ± 2.8
10.4 ± 2.6
11.2 ± 2.7
12.9 ± 2.2
10.1 ± 2.4
9.4 ± 3.3
sec/ FL
53 ± 27
38 ± 17
35 ± 9
35 ± 10

40 ± 12 (calc)

37 ± 10

Summary Data (Excell)

Results from Unrestricted Intake Experiments (Powerpoint)

Statistical tests from Unrestricted Intake Experiments (MS Word)




Nicole Woller
Brandon Hunt
Travis Boyd (Brandon in background)
Kelsi Koenig (Nicole in background)
Travis Boyd
Pilot studies on Peanuts
Additional Questions