Common adage:
The faster you eat, the more you can eat
before getting full.
Background:
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.
or
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.
Results
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.
Conclusions
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.
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