Physiology& Behavior,Vol. 48, pp. 581-586. ©PergamonPress plc, 1990. Printed in the U.S.A.
0031-9384/90 $3.00 + .00
Relationship of Dietary Fat Content to Food Preferences in Young Rats Z O E S. W A R W I C K 1
Department of Psychology, Duke University S U S A N S. S C H I F F M A N
Departments of Psychology and Psychiatry, Duke University AND J O H N J. B. A N D E R S O N
Department of Nutrition, The University of North Carolina-Chapel Hill R e c e i v e d 3 A u g u s t 1990
WARWICK, Z. S., S. S. SCHIFFMAN AND J. J. B. ANDERSON. Relationshipof dietaryfat contenttofood preferences in young rats. PHYSIOL BEHAV 48(5) 581-586, 1990.--Weanling rats were fed either a high-fat (30% of calories) or a low-fat (10% of calories) diet for four weeks, after which fat preference was assessed using a choice paradigm. Fat preference was measured during 2-hour intake tests in which three peanut butter/peanut oil mixtures containing 0.50, 0.61, and 0.71 grams fat/gram were offered to each animal. Rats fed the high-fat (HF) diet preferred the highest-fat mixture and consumed more total fat during intake tests than animals fed the low-fat (LF) diet. Intake of NaCl and sucrose solutions was measured during separate intake tests. LF-fed rats drank more NaC1 solution than HF-fed rats. Following these tests a subgroup of the LF-fed animals was fed the HF diet, and a subgroup of the HF-fed group was fed the LF diet for a further four weeks. Upon repetition of the intake tests, rats that had been fed the HF diet during the intitial four weeks still preferred the highest-fat mixture. Weanling rats
High-fat diet
Dietary fat
Food preferences
SENSORY and ingestive experiences are significant determinants of food selection and intake. A relationship to dietary history has been found for human preferences for salt (1), sucrose (2) and flavors (3, 4, 13). The feeding patterns of rats are similarly linked to prior feeding experiences (5, 6, 8, 10, 11). The purpose of the present study was to determine whether the level of fat in the diet of juvenile rats was related to subsequent preference for fat. Rats were maintained on either a low-fat (10% of calories) or high-fat diet (30% of calories) for four weeks. Following measurements of fat preference a subgroup of the animals was placed on the alternate diet, in order to assess the robustness of food preferences induced by initial dietary experience. Intake of sucrose and sodium chloride solutions was also mea-
sured to determine whether intake of nonfat substances was related to the level of fat in the diet. METHOD
Diets Nutritionally complete diets (see footnote 2) containing either 10% of calories (low-fat) or 30% of calories (high-fat) from safflower oil were prepared weekly by thoroughly mixing all ingredients with an electric mixer (Table 1). The diets were stored at 5°C in sealed plastic tubs. Casein, dextrin, alphacel and mineral mix were obtained from Teldad, Madison, WI. The vitamin mix was obtained from ICN Biomedicals, Cleveland, OH. Safflower oil (Hollywood Brand) and cornstarch (Argo) were purchased lo-
~Requests for reprints should be addressed to Zoe Warwick, Department of Psychology, Duke University, Durham, NC 27706. 2Diets were modified versions of formulations described by R. O. Deems, P. L. Skypala, A. Martinez-Hernandez, L. S. Friedman, M. I. Friedman (personal communication).
581
582
Nutrient Vitamin-free casein Safflower oil Cornstarch Dextrin Sucrose Alphacel Vitamin mix (ICN) Mineral mix (AIN-76) Percentage of Calories Fat Carbohydrate Protein
WARWICK, SCHIFFMAN AND ANDERSON
TABLE 1
TABLE 2
DIET COMPOSITION
FAT-RICH TEST MIXTURES
Low-Fat Diet 118.5 g 21.0 187.5 89.0 31.0 23.5 10.0 19.5 500.0 10 65 25
High-Fat Diet 118.5 74.5 167.5 77.0 24.5 3.5 12.0 22.5 500.0 30 50 20
cally. Sucrose was reagent-grade (Mallinckrodt).
Subjects Two weight-matched groups of weanling female SpragueDawley rats (20 animals per group) were fed either the low-fat (LF) or the high-fat (HF) diet. Rats were aged 21-23 days at the commencement of the experiment and ate the diet ad lib for 4 weeks. This portion of the study was designated "Phase A " and was followed by five to seven consecutive days during which two-hour intake tests (described below) were conducted. Throughout this week of testing the animals continued to eat the diet provided in Phase A. Animals were then fed either the same diet, or the alternate diet for a further four weeks, termed "Phase B . " This yielded four groups of ten animals each (Phase A diet/Phase B diet): LF/LF, LF/HF, HF/LF, HF/HF. Two-hour intake tests were repeated after the second four-week diet phase. Animals were individually housed in standard wire cages in a temperature-controlled (70°F) room. An automatic timer maintained a 12-hour:12-hour light:dark cycle. All testing was conducted midway through the light period and in the animal's home cage.
Composition Per Gram Mixture
Designation
Grams Fat
Grams NaCI
kcal
Peanut Butter 79% Peanut Butter/ 21% Peanut Oil* 59% Peanut Butter/ 41% Peanut Oilt
lowest-fat medium-fat
0.50 0.61
0.013 0.010
5.9 6.6
highest-fat
0.71
0.008
7.2
Peanut butter: Kroger brand, creamy style. Peanut oil: Duke's Brand. *Mixture of I00 g peanut butter and 26 g oil. tMixture of 100 g peanut butter and 70 g oil.
tests. Sucrose preference was measured on the sixth day of the intake tests, using the three-jar choice method. Reagent-grade sucrose (Mallinckrodt) was dissolved (% wt./vol.) in deionized water at two concentrations: 15% and 30%. Preweighed jars of each of these solutions, and a third jar containing deionized water, were placed in each cage for two hours. On the following day, NaCI preference was measured. Reagent-grade NaC1 (Mallinckrodt) was dissolved (% wt./vol.) in deionized water at two concentrations: 0.9% and 1.8%. Preweighed jars of each of these solutions, and a third jar containing deionized water, were placed in each cage for two hours. Only animals maintained on the same diet throughout the study (Groups LF/LF and HF/HF) were tested with these stimuli.
Body Weight Body weight measurements to the nearest gram were obtained twice weekly for all animals.
Data Analysis All data were analyzed using Analysis of Variance for repeated measures (PROC GLM: Statistical Analysis System, release 6.03). RESULTS
Intake Tests
Phase A
Following a five-hour food and water deprivation period, three preweighed 100-ml glass jars containing test stimuli were placed in each animal's home cage and attached to the front wall with wire. The jars were removed after two hours and intake of each stimulus was weighed to the nearest 0.1 g. Dietary fat. Three peanut butter-based mixtures were used to measure preference for novel fat-rich foods. Fat level was manipulated by the addition of peanut oil to peanut butter (Table 2). Rats had access to each of the three mixtures during every test session. Five test sessions were conducted on consecutive days, and the position of the jars was randomized for each animal across the five days. The total grams of fat consumed during each test session was determined for each animal. Total fat intake was calculated by multiplying the quantity consumed of each mixture by the percentage (by weight) of fat it contained (Table 2) and summing these three values. Sucrose and NaCl solutions. Deprivation and measurement conditions were identical to those used in the fat-rich food intake
Body weight. No significant difference was found between the body weights of the two groups immediately prior to intake tests (LF-diet average weight 208 g, s.e. 3.5; HF-diet average weight 213 g, s.e. 3.6), F(1,38)=0.89, NS. Intake of fat-rich mixtures. Animals fed a high-fat diet ate somewhat more fat from the mixtures on all test days relative to animals fed a low-fat diet (Fig. 1), although the main effect of diet did not reach statistical significance, F(1,38) = 2.47, NS. The difference in total consumption between groups was mainly due to greater intake of the highest-fat mixture by the HF-fed animals (Fig. 2). An increase in intake across the five test days was noted for both groups (Fig. 1), which was confirmed statistically by the main effect of trials, F(4,35) = 8.0, p
0031-9384/90 $3.00 + .00
Relationship of Dietary Fat Content to Food Preferences in Young Rats Z O E S. W A R W I C K 1
Department of Psychology, Duke University S U S A N S. S C H I F F M A N
Departments of Psychology and Psychiatry, Duke University AND J O H N J. B. A N D E R S O N
Department of Nutrition, The University of North Carolina-Chapel Hill R e c e i v e d 3 A u g u s t 1990
WARWICK, Z. S., S. S. SCHIFFMAN AND J. J. B. ANDERSON. Relationshipof dietaryfat contenttofood preferences in young rats. PHYSIOL BEHAV 48(5) 581-586, 1990.--Weanling rats were fed either a high-fat (30% of calories) or a low-fat (10% of calories) diet for four weeks, after which fat preference was assessed using a choice paradigm. Fat preference was measured during 2-hour intake tests in which three peanut butter/peanut oil mixtures containing 0.50, 0.61, and 0.71 grams fat/gram were offered to each animal. Rats fed the high-fat (HF) diet preferred the highest-fat mixture and consumed more total fat during intake tests than animals fed the low-fat (LF) diet. Intake of NaCl and sucrose solutions was measured during separate intake tests. LF-fed rats drank more NaC1 solution than HF-fed rats. Following these tests a subgroup of the LF-fed animals was fed the HF diet, and a subgroup of the HF-fed group was fed the LF diet for a further four weeks. Upon repetition of the intake tests, rats that had been fed the HF diet during the intitial four weeks still preferred the highest-fat mixture. Weanling rats
High-fat diet
Dietary fat
Food preferences
SENSORY and ingestive experiences are significant determinants of food selection and intake. A relationship to dietary history has been found for human preferences for salt (1), sucrose (2) and flavors (3, 4, 13). The feeding patterns of rats are similarly linked to prior feeding experiences (5, 6, 8, 10, 11). The purpose of the present study was to determine whether the level of fat in the diet of juvenile rats was related to subsequent preference for fat. Rats were maintained on either a low-fat (10% of calories) or high-fat diet (30% of calories) for four weeks. Following measurements of fat preference a subgroup of the animals was placed on the alternate diet, in order to assess the robustness of food preferences induced by initial dietary experience. Intake of sucrose and sodium chloride solutions was also mea-
sured to determine whether intake of nonfat substances was related to the level of fat in the diet. METHOD
Diets Nutritionally complete diets (see footnote 2) containing either 10% of calories (low-fat) or 30% of calories (high-fat) from safflower oil were prepared weekly by thoroughly mixing all ingredients with an electric mixer (Table 1). The diets were stored at 5°C in sealed plastic tubs. Casein, dextrin, alphacel and mineral mix were obtained from Teldad, Madison, WI. The vitamin mix was obtained from ICN Biomedicals, Cleveland, OH. Safflower oil (Hollywood Brand) and cornstarch (Argo) were purchased lo-
~Requests for reprints should be addressed to Zoe Warwick, Department of Psychology, Duke University, Durham, NC 27706. 2Diets were modified versions of formulations described by R. O. Deems, P. L. Skypala, A. Martinez-Hernandez, L. S. Friedman, M. I. Friedman (personal communication).
581
582
Nutrient Vitamin-free casein Safflower oil Cornstarch Dextrin Sucrose Alphacel Vitamin mix (ICN) Mineral mix (AIN-76) Percentage of Calories Fat Carbohydrate Protein
WARWICK, SCHIFFMAN AND ANDERSON
TABLE 1
TABLE 2
DIET COMPOSITION
FAT-RICH TEST MIXTURES
Low-Fat Diet 118.5 g 21.0 187.5 89.0 31.0 23.5 10.0 19.5 500.0 10 65 25
High-Fat Diet 118.5 74.5 167.5 77.0 24.5 3.5 12.0 22.5 500.0 30 50 20
cally. Sucrose was reagent-grade (Mallinckrodt).
Subjects Two weight-matched groups of weanling female SpragueDawley rats (20 animals per group) were fed either the low-fat (LF) or the high-fat (HF) diet. Rats were aged 21-23 days at the commencement of the experiment and ate the diet ad lib for 4 weeks. This portion of the study was designated "Phase A " and was followed by five to seven consecutive days during which two-hour intake tests (described below) were conducted. Throughout this week of testing the animals continued to eat the diet provided in Phase A. Animals were then fed either the same diet, or the alternate diet for a further four weeks, termed "Phase B . " This yielded four groups of ten animals each (Phase A diet/Phase B diet): LF/LF, LF/HF, HF/LF, HF/HF. Two-hour intake tests were repeated after the second four-week diet phase. Animals were individually housed in standard wire cages in a temperature-controlled (70°F) room. An automatic timer maintained a 12-hour:12-hour light:dark cycle. All testing was conducted midway through the light period and in the animal's home cage.
Composition Per Gram Mixture
Designation
Grams Fat
Grams NaCI
kcal
Peanut Butter 79% Peanut Butter/ 21% Peanut Oil* 59% Peanut Butter/ 41% Peanut Oilt
lowest-fat medium-fat
0.50 0.61
0.013 0.010
5.9 6.6
highest-fat
0.71
0.008
7.2
Peanut butter: Kroger brand, creamy style. Peanut oil: Duke's Brand. *Mixture of I00 g peanut butter and 26 g oil. tMixture of 100 g peanut butter and 70 g oil.
tests. Sucrose preference was measured on the sixth day of the intake tests, using the three-jar choice method. Reagent-grade sucrose (Mallinckrodt) was dissolved (% wt./vol.) in deionized water at two concentrations: 15% and 30%. Preweighed jars of each of these solutions, and a third jar containing deionized water, were placed in each cage for two hours. On the following day, NaCI preference was measured. Reagent-grade NaC1 (Mallinckrodt) was dissolved (% wt./vol.) in deionized water at two concentrations: 0.9% and 1.8%. Preweighed jars of each of these solutions, and a third jar containing deionized water, were placed in each cage for two hours. Only animals maintained on the same diet throughout the study (Groups LF/LF and HF/HF) were tested with these stimuli.
Body Weight Body weight measurements to the nearest gram were obtained twice weekly for all animals.
Data Analysis All data were analyzed using Analysis of Variance for repeated measures (PROC GLM: Statistical Analysis System, release 6.03). RESULTS
Intake Tests
Phase A
Following a five-hour food and water deprivation period, three preweighed 100-ml glass jars containing test stimuli were placed in each animal's home cage and attached to the front wall with wire. The jars were removed after two hours and intake of each stimulus was weighed to the nearest 0.1 g. Dietary fat. Three peanut butter-based mixtures were used to measure preference for novel fat-rich foods. Fat level was manipulated by the addition of peanut oil to peanut butter (Table 2). Rats had access to each of the three mixtures during every test session. Five test sessions were conducted on consecutive days, and the position of the jars was randomized for each animal across the five days. The total grams of fat consumed during each test session was determined for each animal. Total fat intake was calculated by multiplying the quantity consumed of each mixture by the percentage (by weight) of fat it contained (Table 2) and summing these three values. Sucrose and NaCl solutions. Deprivation and measurement conditions were identical to those used in the fat-rich food intake
Body weight. No significant difference was found between the body weights of the two groups immediately prior to intake tests (LF-diet average weight 208 g, s.e. 3.5; HF-diet average weight 213 g, s.e. 3.6), F(1,38)=0.89, NS. Intake of fat-rich mixtures. Animals fed a high-fat diet ate somewhat more fat from the mixtures on all test days relative to animals fed a low-fat diet (Fig. 1), although the main effect of diet did not reach statistical significance, F(1,38) = 2.47, NS. The difference in total consumption between groups was mainly due to greater intake of the highest-fat mixture by the HF-fed animals (Fig. 2). An increase in intake across the five test days was noted for both groups (Fig. 1), which was confirmed statistically by the main effect of trials, F(4,35) = 8.0, p
