Journal of Comparative and Physiological Psychology
1966, Vol. 61, No. 1, 1-4
NOVEL FOOD PREFERENCES IN THIAMINE-DEFICIENT RATS1
WILLARD RODGERS AND PAUL ROZIN
University of Pennsylvania
Thiamine-deficient rats choosing between a novel diet and a familiar diet invariably showed a marked preference for the novel diet. If the novel diet contained thiamine, this preference was maintained over a 10-day period. If the
novel diet was deficient in thiamine, and thiamine was added to the familiar
diet, Ss switched from an initial novel diet preference to a familiar diet preference after 3-4 days. Control rats showed no preferences for either diet.
The exclusive initial ingestion of a novel diet may facilitate the development
of a sustained, learned preference.
with eating that particular diet. (6) Thiamine-deficient rats injected with large
quantities of thiamine from 12 hr. to 10 days
before being offered a choice between a
deficient and a thiamine-containing diet
nevertheless show a strong preference for
the thiamine diet, even though the thiamine
ingested orally presumably has no effect
(Rozin, 1965). (c) No preference is observed when thiamine is in one of two bottles of water, in spite of the fact that
thiamine produces the same physiological
effects in the rat whether ingested in water
or food (Rozin, Wells, & Mayer, 1964).
The situation, therefore, remains unclear,
insofar as the explanations of thiamine
preference (as innate and as learned) seem
equally inadequate. It may be, however,
that while neither explanation is correct in
itself, there is some truth in each. Perhaps
there is an instinctive feeding pattern in
the thiamine-deficient rat which maximizes
the possibility of learning. An analogous
explanation has been offered for the reaction of wild rats to poisoned foods (Rzoska,
1953). Rats that have been poisoned sometimes develop a reluctance to eat new
foods. When they finally try a new food,
they frequently take only a few nibbles
and then leave the food for a period of time
before eating more. This sampling method
would apparently maximize the possibility
of associating ill effects with a particular
food. It is possible that a similar, but reversed, response to new foods is present in
the thiamine-deficient rat. Our casual observations indicated that these rats re1
This research was supported by National Sci- sponded readily to novel foods, and sugence Foundation Grant GB-1489.
* gested the experiment that is reported here.
That thiamine (vitamin Bl) deficient rats
prefer foods containing thiamine has been
known for years, but very little is known
about the mechanism of the preference.
Some of Richter's work (e.g., Richter, Holt,
& Barelare, 1937) suggests that many preferences based on dietary deficiencies may involve innate recognition of the needed component. One difficulty with this explanation
is the failure of an immediate response to
thiamine to appear reliably in deficient
rats. Furthermore, if thiamine is initially
paired with a distinctive flavor and afterwards switched to a diet with a different
flavor, thiamine-deficient rats continue to
prefer the diet with which the thiamine was
originally associated (Harris, Clay, Hargreaves, & Ward, 1933; Scott & Verney,
1947).
Most investigators believe that thiamine
preference is learned: ingestion of thiamine-rich foods makes the thiamine-deficient rat feel better. This explanation of
thiamine hunger by a simple reinforcement
mechanism also runs into a number of difficulties, (a) Ingestion of thiamine would
not have any beneficial effects for at least
10 min., and probably not for 30 min., and
learning does not ordinarily take place with
such a long delay of reinforcement. Furthermore, a normal rat in a preferencetesting situation frequently samples from
the dietary choices available. Unless there
is a mechanism operative in the deficient
rat which results in an exclusive choice of
the thiamine-containing diet, thiamine's
beneficial effects would not be associated
WILLARD RODGERS AND PAUL ROZIN
DEFICIENT GROUP
NOVEL DIET 1
THIAMINE IN NOVEL DIET
THIAMINE IN FAMILIAR DIET
recorded daily and also frequently during the first
8 hr. on the first day. The general procedure used
was identical to that of Rozin, Wells, and Mayer
(1964).
The experiment was repeated with four additional groups of three Ss, using a second novel
diet very different from both the first novel diet
and the standard diet so as to test the generality
of the results.
RESULTS
The results of the basic experiment are
shown in Figures 1 and 2. Deficient rats in
both groups showed an unequivocal, immediate, initial preference for the novel diet, regardless of whether or not it contained thiamine. The preference appeared clearly
within 15 min. of first presentation. Very
FIG. 1. Preference for first novel diet by thia- little, if any, familiar diet was eaten in the
mine-defioient rats over a 10-day experimental first 8 hr. The avid response of the deficient
period. [Preference is expressed as: (novel diet rats to the novel food was in marked coneaten/total diet eaten) X 100 for each day.] Each trast to their anorexia preceding presentablock represents the daily preferences of one rat
tion of the novel diet. The deficient rats
for 10 days.
which were given a choice between a novel
diet with thiamine and the standard diet
METHOD
without thiamine maintained the prefFour groups of three rats (Charles River, female, CD Sprague-Dawley strain) were fed a erence for the novel diet throughout the
standard synthetic thiamine-deficient diet for the 10-day choice period. The deficient rats
first 3 wk. of the experiment.2 All Ss were 21-day- which were given a choice between a novel
old weanlings at the beginning of the experiment. diet without thiamine and the standard
Six Ss (in the two control groups) were injected diet with thiamine ate very small amounts
with thiamine subcutaneously throughout the experiment, so that they never became deficient; of food (about 5 gm/day) during the first
however, the amount of food given to them each few days, since they were eating the novel
day during the first 3 wk. was restricted so as to deficient diet almost exclusively. They
keep their weight equal to that of the deficient showed a sharp change in diet preference on
rats.
At the end of 3 wk. on deficient diet, the uninjected & were losing weight rapidly, a clear sign
of thiamine deficiency. Each S in the four groups
was then offered a choice between the standard
(familiar) diet and a novel diet for 10 days. For one
group of deficient Ss and one control group, thiamine (20 jug/gm) was added to the novel diet but
not to the standard diet; for the other two groups,
thiamine was added to the standard diet but not
to the novel diet. Food intakes of both diets were
2
All diets were mixed in the laboratory from
standard synthetic components and contained 1%
thiamine-deficient vitamin mix in sucrose (General Biochemicals) and 4% Hegsted salt mix. The
standard diet contained, in addition, 3% Mazola,
2% cod liver oil, 65% sucrose, 25% casein. The
first novel diet contained 10% peanut oil, 45%
sucrose, 10% starch, 15% casein, and 15% soy
protein. The second novel diet contained 10%
Mazola, 40% sucrose, 15% casein, and 30% gelatin. In thiamine-containing diets, the thiamine
concentration was always 20 /ig/gm.
PAIR-WEIGHED CONTROL GROUP
NOVEL DIET 1
THIAMINE IN NOVEL DIET
THIAMINE IN FAMILIAR DIET
10
FIG. 2. Preference for first novel diet by control
rats, plotted as in Figure 1.
NOVEL FOOD PREFERENCES
the fourth choice day, selecting the standard
diet with added thiamine on each of the last
7 days, and showing a marked increase in
total daily food intake. The rats in the control groups showed no significant preference
for either the standard or the novel diet
throughout the 10-day choice period.
In the repetition of the experiment with
another novel diet, a large initial preference for the novel diet was again shown by
both groups of deficient rats, whereas a
slight avoidance of this diet was shown by
the two groups of control rats (Figures 3
and 4). During the 10-day choice period,
each control group showed a three-to-one
preference for the standard diet. The deficient group whose novel diet contained thiamine showed a two-to-one preference for the
novel diet. The deficient group whose
standard diet contained thiamine showed a
four-to-one preference for the novel diet
on each of the first 3 days, but on the last
6 days a preference for the standard diet.
DISCUSSION
This experiment shows that thiamine-deficient rats change their feeding patterns
and invariably prefer novel diets. The preference for a new diet may reflect either an
increased desire for novel foods or an acquired aversion to the familiar diet. Such
a preference for new foods by deficient rats
DEFICIENT GROUP
NOVEL DIET 2
THIAMINE IN NOVEL DIET
25
THIAMINE IN FAMILIAR DIET
28
FIG. 3. Preference for second novel diet by thiamine-deficient rats, plotted as in Figure 1. (Rat 29
was almost dead by Day 5 as he ingested very little
thiamine, so the experiment was terminated.)
PAIR-WEIGHED CONTROL GROUP
NOVEL DIET 2
THIAMINE IN NOVEL DIET
THIAMINE IN FAMILIAR DIET
31
34
FIG. 4. Preference for second novel diet by control rats, plotted as in Figure 1.
in the natural situation would maximize
the likelihood of encountering the needed
substance. Given that this initial preference for novel diets is innate, the question
remains as to what maintains the preference, or what causes the rats to revert to the
familiar diet when thiamine has been
added to it. It is here that a learning mechanism may have its function.
When the deficient rat is confronted with
a choice between a novel and a familiar
diet, it initially prefers the novel diet. If
this novel diet contains the needed thiamine, the beneficial effects of ingesting this
diet may reinforce the novel preference.
The fact that the rat eats almost exclusively from the novel diet, in conjunction
with the distinctive characteristics of .this
diet, makes it more reasonable to assume
that the beneficial effects of the ingested
thiamine will reinforce the particular response of eating this diet. In the first few
hours after the first meal, the effects of previously ingested thiamine should result in
gradual recovery of the deficient rat. Thus
recovery would be taking place during the
subsequent meal periods when the rat is
again consuming the novel diet. If the novel
diet contains no thiamine, a preference for
the familiar diet develops after 3-4 days.
The mechanism underlying this shift is still
unknown, but it is probably some process independent of the novelty of the diet.
WILLARD RODGERS AND PAUL ROZIN
In most specific hunger experiments, the
deficient rats have been offered a choice
between the old, familiar diet and a
slightly novel, new, vitamin-rich diet. On
the basis of the results of the present experiment, it appears that the standard specific hunger paradigm fails to indicate
whether the needed substance is preferred
because of its novelty or because of its
specific properties. In other words, it is not
clear that most specific hungers have really
been shown to be specific. Adequate controls have indicated true specificity in sodium hunger. (Nachman, 1962), but similar
controls have not been used in most other
cases.
These experiments raise several interesting questions. For instance, is the needed
component (in this case thiamine) more effective than an arbitrary substance as a
novel stimulus? Must the thiamine be part of
the novel diet to maintain the initial preference, or would injections of thiamine be
just as effective? Do deficiencies in other
substances also result in a novel diet preference? Is the failure of a specific hunger
for thiamine to appear in a liquid choice
situation related to the absence of a novelty response to liquids? Does this novelty
preference explain the preference for thiamine diets by rats previously recovered
from thiamine deficiency? Is the change in
response to novelty limited to foods, or
does it extend to other aspects of the environment?
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NACHMAN, M. Taste preferences for sodium salts
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RICHTEH, C. P., HOLT, L. E., & BARBLARB, B., JR.
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ROZIN, P. Specific hunger for thiamine: Recovery
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(Received March 1, 1965)