| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Obesity, These
experiments were designed to test the hypothesis that the contrasting
patterns of macronutrient selection described previously in AKR/J (fat
preference) and SWR/J (carbohydrate preference) mice are not dependent
on a single diet paradigm. The effect of mouse strain on proportional
fat intake was tested in naive mice by presenting two-choice diets
possessing a variety of physical, sensory, and nutritive properties. In
three separate experiments, AKR/J mice preferentially selected and
consumed a higher proportion of energy from the high-fat diet than
SWR/J mice. Specifically, this phenotypic difference was observed with
1) fat-protein vs. carbohydrate-protein diets, independent of fat type (vegetable shortening or lard), 2) isocaloric,
high- vs. low-fat liquid diet preparations, and
3) high- vs. low-fat
powdered-granular diets. These results confirm our previous observation
of a higher proportional fat intake by AKR/J compared with SWR/J mice
using the three-choice macronutrient selection diet and show that this
strain difference generalizes across several diet paradigms. This
strain difference is due largely to the robust and reliable fat
preference of the AKR/J mice. In contrast, macronutrient preference in
SWR/J mice varied across paradigms, suggesting a differential response
by this strain to some orosensory or postingestive factor(s).
carbohydrate; macronutrient; diet selection; dietary obesity; liquid diet; saturated fat
LARGE DIFFERENCES in individuals' preferences for
dietary fat have been reported (7, 14). However, the fundamental cause of these preferences has not been shown. Preferences for high-fat foods
can be learned (12) and are correlated with familial adiposity (8),
indicating the importance of environmental factors. An interaction
between environmental and genetic factors is supported by the
observations of differences in susceptibility to obesity in the
presence of high dietary fat intake (9) and evidence that human dietary
fat preference is linked to body weight status (17). Although there
have been few studies assessing the possible genetic basis for food
preferences, preferences for high-fat foods may have a heritable
component (23). If fat selection/consumption is a key factor in the
expression of obesity (31), then an investigation of the possible
genetic basis for this behavior is warranted.
As a necessary step toward developing an animal model to characterize
genetic and behavioral factors linked to the preferential intake of
dietary fat, we have investigated the generality of a model of
contrasting patterns of macronutrient selection previously demonstrated
in two inbred mouse strains: AKR/J mice select a higher proportion of
energy from fat, whereas the SWR/J mice select a higher proportion of
carbohydrate when offered separate sources of the three macronutrients
(27). The observation of contrasting patterns of dietary selection in
these strains parallels their differential sensitivity to dietary
obesity described previously, i.e., AKR/J mice increase adiposity
approximately threefold, whereas SWR/J mice remain relatively lean when
fed a moderately high-fat diet (29). Thus the higher voluntary fat
consumption by AKR/J mice suggests a possible relationship between
sensitivity to dietary obesity and a preference for eating high-fat
food. Alternatively, a relationship may exist between fat avoidance or
carbohydrate preference and resistance to dietary obesity.
This experimental model could be paradigm specific. Therefore the
purpose of these studies was to assess the generality of our previous
observations of differential macronutrient selection by evaluating the
impact of three different diet paradigms on macronutrient selection in
AKR/J and SWR/J mice. The following questions were addressed.
Will changing the fat type alter the pattern of macronutrient
selection? There is evidence that animals fed saturated fat diets
self-select a high-protein, low-carbohydrate diet, whereas animals fed
unsaturated fat prefer a low-protein, high-carbohydrate diet when total
fat composition is held constant (15-16, 18). To determine if
saturated fat level influences fat selection, a choice paradigm was
used in which the fat-protein diet contained either hydrogenated
vegetable shortening or lard with 78% of calories from fat. The
carbohydrate-protein diet provided 78% of calories from carbohydrate.
Will liquid form and isocaloric content of the diets alter
macronutrient selection? One criticism of macronutrient selection paradigms is that the individual diets vary considerably with respect
to texture and caloric density, thereby influencing animals to select
diets for factors other than nutrient composition (2, 14). To control
for these factors, suspendible high- and low-fat diet mixtures were
used, each containing all three macronutrients. The two diets were also
isocaloric, thus eliminating the possibility that an animal would
select a particular diet for its energy density rather than its
nutritional content.
Will powdered form alter the pattern of macronutrient selection in
AKR/J and SWR/J mice? Diet selection may be influenced by textural
preferences (1, 5, 14). Another criticism of diet selection studies is
the potential artificiality of using choice paradigms in which
individual preparations lack one or more macronutrients, e.g., the
fat-protein and carbohydrate-protein diets described above require rats
to compose their own nutritionally complete diet. Therefore in this
experiment two nutritionally complete, dry powdered diets were presented.
Therefore, the present experiments were conducted in separate groups of
naive mice to test the generality of high-fat vs. low-fat diet
preference with respect to a variety of physical, sensory, and
nutritive properties of diets.
Animals
ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS AND PROCEDURES
RESULTS
DISCUSSION
REFERENCES
INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS AND PROCEDURES
RESULTS
DISCUSSION
REFERENCES
METHODS AND PROCEDURES
TOP
ABSTRACT
INTRODUCTION
METHODS AND PROCEDURES
RESULTS
DISCUSSION
REFERENCES
Procedures
Two-choice semisolid composite diets. A choice of either a carbohydrate-protein diet containing 78 and 22% of energy from carbohydrate and protein, respectively, or a fat-protein diet containing 78 and 22% of energy from fat and protein, respectively, was provided (see Table 1). The fat-protein diet contained either vegetable shortening or lard. The fat-protein diet at room temperature was in the form of an oily paste. The carbohydrate-protein diet was a dry, powdery mixture of finely milled (cornstarch and powdered sugar) and small granular particles (casein). Each of the two diets was presented in a custom 2-oz glass jar (Unifab, Kalamazoo, MI). The jars were covered with stainless steel lids with openings that measured
in. in diameter. Jars and
spillage were weighed to the nearest 0.1 g using the same balance
(PM300, Mettler-Toledo, Hightstown, NJ) throughout the study. To ensure freshness against oxidation, the jars containing fat were changed every
48 h. Jars containing carbohydrate and protein were topped off with
fresh diet every 48 h and changed weekly. Animals had ad libitum access
to the diets for a total of 30 days; 48-h intake of individual diets,
including all spillage, was measured throughout this period. Because
adiposity and body fat distribution can be influenced by type of
dietary fat (11, 12), two separate control groups of six mice per
strain received rodent chow for the same period of time. The chow diet
(metabolizable energy, 3.30 kcal/g) was composed of 28% protein, 12%
fat, and 60% carbohydrate (% of energy; Purina #5001).
|
Two-choice isocaloric liquid composite diets. A choice of either a high-fat (HF) or low-fat (LF) liquid diet was provided for 22 h daily at the beginning of the dark cycle. Each diet was nutritionally complete and formulated by Research Diets (New Brunswick, NJ; see Table 1). The HF diet contained 45% of calories from fat (corn oil) and 40% of calories from carbohydrate (maltodextrin). The LF diet contained 5% fat and 80% carbohydrate. Both liquid diet preparations were isocaloric (1.0 kcal/ml) and contained the same percentage of calories from protein (15%). Diets were prepared fresh daily by suspending the premixes in water using a benchtop homogenizer (PRO Scientific; 15,000 rpm × 10 min) and then quickly cooling the suspensions to room temperature. Diet suspensions were presented in 50-ml conical cylinders with rubber stoppers and stainless steel sipper tubes with 2.5-mm openings. There was a distance of 8.4 cm between the two spout openings, and the left/right position of the cylinders was alternated every 24 h to control for side preferences. Twenty-two-hour intake of both diets was measured daily by weighing the cylinders to the nearest 0.1 g; ~2 h/day were required to weigh and replace diet tubes with cleaned and refilled tubes. Animals had ad libitum access to the diets for a total of 20 days; 24-h intake of individual diets was measured throughout this period.
Two-choice powdered composite diets. A choice of either a high-fat powdered (HFP) or low-fat powdered (LFP) diet was provided; each diet was nutritionally complete and formulated by Research Diets (see Table 1). The HFP diet contained 45% of calories from fat (corn oil and vegetable shortening), 40% of calories from carbohydrate (cornstarch and sucrose), and 15% calories from protein (casein). The LFP diet contained 5% fat and 80% carbohydrate. The carbohydrate source in both diet preparations contained the same sucrose-to-cornstarch ratio. Thus the HFP diet had a granular, slightly oily texture, and the LFP diet had a dry, powdery-granular texture. Animals had ad libitum access to the diets for a total of 25 days; 24-h intake of individual diets, including all spillage, was measured throughout this period.
The casein sources used in the experimental diets varied slightly in total sulfur amino acid (SAA) content. The laboratory animal nutrient requirement for SAA is 0.6% in growing mice and 0.23% in mature animals (one-half of this requirement must be supplied by L-methionine) (20). The diets used in experiment 1 were composed in our laboratory (see Table 1) using lactic casein (ICN Biomedicals, Costa Mesa, CA); these diets provided 0.47% methionine from the casein component and were supplemented with an additional 0.29% methionine. In experiments 2 and 3, the custom commercial diets (see Table 1; Research Diets) contained lactic casein (New Zealand Milk Products, Santa Rosa, CA), which provided 0.40% methionine from the casein component and 0.15% of additional cystine. In the present study, animals were mature (7-8 wk) at the time of diet presentation and thus were adequately supplemented by these diet preparations.
Dissection
At the end of experiment 1, mice were killed by cervical dislocation. The carcass was dissected, and the spleen, liver, and kidneys were removed and weighed. The following fat depots were removed and weighed: left and right inguinal, left and right epididymal, left and right retroperitoneal, and mesenteric. An adiposity index was calculated by dividing the summed weight of these adipose depots by the weight of the carcass (minus the adipose depots) (30).Data Analysis
Dietary intakes were examined in three forms: grams, kilocalories, and as proportion of total kilocalories. Within-strain analyses of the effect of diet choice revealed the diet "preference" of the animals when expressed as units of volume (g) or as energy consumed (kcal). Proportional intake of the high-fat diet was used for comparisons between strains, thus controlling for differences in body size and total food intake. Repeated measures ANOVA using a mixed model was used to evaluate the main effects of diet (choice), fat type, or time on food intake. The covariance matrix was assessed using the autoregressive type I structure. Individual comparisons were evaluated using the Bonferroni correction. In experiment 2, the left/right position of cylinders containing liquid diets was alternated every 24 h to control for side preferences; the 48-h value used in the analyses was the sum of two 24-h intakes.| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND PROCEDURES
RESULTS
DISCUSSION
REFERENCES
|
|---|
Experiment 1: Two-Choice Semisolid Composite Diets (g)
Figure 1 depicts mean 48-h food intakes in grams by self-selecting AKR/J (Fig. 1A) and SWR/J (Fig. 1B) mice. The effect of fat type (lard, vegetable shortening) on gram intake of the fat-protein and carbohydrate-protein diets was examined by strain and diet. In AKR/J mice, there were no effects of fat type on overall gram intake of the carbohydrate-protein [F(1,21) = 3.66, P = 0.07] or fat-protein [F(1,22) = 3.22, P = 0.09] diets (Fig. 1A). An analysis of diet selection across the 30-day study revealed that AKR/J mice in the vegetable shortening fat (Veg) group consumed more grams of fat-protein than of the carbohydrate-protein diet [F(1,280) = 9.34, P < 0.005], and this pattern was consistent across the study [F(14,280) = 1.21, P = 0.26]. For the mice in the lard fat (Lard) group, however, there was not a reliable difference in the weight of food consumed from the fat-protein and the carbohydrate-protein diets [F(1,307) = 3.24, P = 0.07]. Specifically, AKR/J mice in the Lard group selected more of the carbohydrate-protein than the fat-protein diet in the first half of the study, but on day 16 (P = 0.18) they began consuming equivalent amounts (g) from both diets [F(14,307) = 2.80, P = 0.001] (Fig. 1A).
|
In SWR/J mice, there were significant effects of fat type on gram intake of both the fat-protein [F(1,22) = 7.21, P < 0.05] and carbohydrate-protein [F(1,22) = 6.34, P < 0.05] diets, i.e., SWR/J mice in the Lard group consumed even more grams of the carbohydrate-protein diet and less from the fat-protein diet than did self-selecting mice in the Veg group (Fig. 1B). However, an ANOVA for diet selection by fat type showed that self-selecting SWR/J mice significantly preferred the carbohydrate-protein compared with the fat-protein diet, with respect to grams, regardless of whether the fat source was lard [F(1,319) = 246.75, P < 0.0001] or vegetable shortening [F(1,319) = 50.42, P < 0.0001] (Fig. 1B). There was fluctuation in these diet selection patterns over time [Lard, F(14,319) = 3.38, P < 0.0001; Veg, F(14,319) = 2.71, P < 0.0001].
Experiment 1: Two-Choice Semisolid Composite Diets (kcal, Proportion)
Figure 2 depicts mean 48-h food intakes in kilocalories by self-selecting AKR/J (Fig. 2A) and SWR/J (Fig. 2B) mice. The effect of fat type (lard, vegetable shortening) on kilocalorie intake of the fat-protein and carbohydrate-protein diets was examined within each strain. In AKR/J mice, there were no reliable effects of fat type on intake of the carbohydrate-protein [F(1,21) = 3.66, P = 0.07] or fat-protein [F(1,22) = 3.22, P = 0.09] diets (Fig. 2A). An analysis of diet selection during the 30-day study revealed that AKR/J mice in the Veg group consumed more calories from the fat-protein than from the carbohydrate-protein diet [F(1,280) = 66.46, P < 0.0001], and this pattern was consistent across the study [F(14,280) = 1.34, P = 0.18]. AKR/J mice in the Lard group also consumed more calories from the fat-protein than from the carbohydrate-protein diet [F(1,307) = 15.09, P < 0.0001]. In contrast to the Veg group, AKR/J mice in the Lard group increased fat-protein diet intake and decreased carbohydrate-protein diet intake over time [F(14,307) = 2.53, P = 0.002]. With respect to calories, AKR/J mice in the Lard group did not show a preference for the fat-protein diet until days 15-16 of the experiment (P < 0.05) (Fig. 2).
|
In SWR/J mice, there were significant effects of fat type on kilocalorie intake of both the fat-protein [F(1,22) = 7.21, P < 0.05] and carbohydrate-protein [F(1,22) = 6.34, P < 0.05] diets, i.e., SWR/J mice in the Lard group consumed even more kilocalories from the carbohydrate-protein diet and less from the fat-protein diet than did self-selecting mice in the Veg group (Fig. 2B). However, ANOVA for diet selection by fat type showed that self-selecting SWR/J mice significantly preferred the carbohydrate-protein compared with the fat-protein diet regardless of whether the fat source was lard [F(1,319) = 136.23, P < 0.0001] or vegetable shortening [F(1,319) = 8.96, P < 0.005] (Fig. 2B). These diet selection patterns fluctuated over time [Lard, F(14,319) = 2.75, P < 0.001; Veg, F(14,319) = 2.54, P < 0.005].
Figure 3 illustrates the proportion of
total calories consumed from the fat-protein diet by each of the two
mouse strains when the fat source was lard (Fig.
3A) or vegetable shortening (Fig.
3B). Overall, self-selecting AKR/J
mice consumed a greater proportion of total energy from the fat-protein
diet than SWR/J mice whether the primary fat source was lard
[F(1,22) = 24.15, P < 0.0001] or vegetable
shortening [F(1,21) = 13.47, P < 0.002]. However,
proportional intake of the Veg fat-protein diet tended to be higher for
both AKR/J (0.65-0.77) and SWR/J (0.38-0.49) mice compared
with their intake of the Lard fat-protein diet (AKR/J, 0.50-0.64;
SWR/J, 0.24-0.44).
|
Experiment 1: Two-Choice Semisolid Composite Diets (Total kcal, Body Weight, Adipose Depot, and Organ Weight)
There was a significant effect of mouse strain [F(1,53) = 141.93, P < 0.0001] but not of diet [F(2,53) = 1.83, P = 0.17] on total caloric intake across the study (Fig. 4A); i.e., within each diet group AKR/J mice consumed more energy than SWR/J mice. Body weight gain in the two strains fed chow was similar when averaged across the study period, whereas body weight of the self-selecting AKR/J mice in both the Lard (P < 0.0001) and Veg (P < 0.0001) protocols increased more than SWR/J (Fig. 4B). In addition, self-selecting AKR/J mice in the two-choice diet protocols weighed significantly more than AKR/J mice fed chow beginning on day 15 (P < 0.01) and continuing to the end of the study whether the fat type was vegetable shortening or lard, as indicated by the significant interaction of mouse strain × diet × time [F(26,52) = 3.36, P < 0.0001] (Fig. 4B). However, diet type had no effect on the body weight of SWR/J mice at any time measured.
|
Adipose depot and organ weights as well as adiposity index for the
chow-fed and self-selecting groups are presented in Table 2. At the end of the 30-day study,
self-selecting AKR/J mice in the two-choice paradigm, independent of
fat type, were fatter than AKR/J mice fed chow as reflected by the
larger size of four different adipose tissue depots resulting in a
higher adiposity index [F(2,26) = 25.08, P < 0.0001]. There
was no effect of diet group on any of the organ weights in this strain.
Although diet group had no effect on body weight in SWR/J mice, there
was a significant effect of diet on adiposity index in this strain
[F(2,27) = 3.76, P < 0.05] due primarily to
larger retroperitoneal and inguinal fat depots in self-selecting
animals in the Lard protocol compared with the chow-fed group (see
Table 2). The SWR/J mice in the Lard group also had smaller liver
weights compared with the chow-fed or SWR/J mice in the Veg groups, as
well as smaller spleen weights compared with the Veg group.
|
Experiment 2: Two-Choice Liquid Composite Diets
Figure 5 depicts mean 48-h food intakes by self-selecting AKR/J (Fig. 5A) and SWR/J (Fig. 5B) mice. AKR/J mice consumed more energy from the HF liquid diet than the LF [F(1,247) = 33.58, P < 0.0001] during the first 12 days (P < 0.05, Bonferroni). Thus the initial HF preference of AKR/J mice disappeared over time [F(9,247) = 7.57, P < 0.0001]. In contrast, SWR/J mice consumed equivalent amounts of the HF and LF liquid diets throughout the study [F(1,228) = 0.45, P = 0.50]. However during the first 4 days, SWR/J mice tended to consume more of the HF diet [F(9,228) = 3.39, P < 0.001]. Figure 6 illustrates the proportion of total calories consumed from the HF diet by both strains. Compared with SWR/J mice, self-selecting AKR/J mice consumed a greater proportion of total energy from the HF diet [F(1,25) = 5.39, P < 0.05]. This strain difference disappeared over time due to the decline in proportional fat intake by AKR/J mice [strain × time interaction: F(9,25) = 3.11, P < 0.05].
|
|
Age-matched AKR/J mice normally weigh more than SWR/J mice at baseline
[F(1,24) = 214.26, P < 0.0001]. With liquid
choice diets, both strains significantly increased body weight over
time, but the AKR/J mice gained more than SWR/J mice [strain × time interaction: F(9,24) = 9.94, P < 0.0001] (Fig.
7).
|
Experiment 3: Two-Choice Powdered Composite Diets
Figures 8 and 9 depict mean 24-h food intakes by self-selecting AKR/J (Figs. 8A and 9A) and SWR/J (Figs. 8B and 9B) mice. Overall, both AKR/J and SWR/J mice consumed more energy from the HFP than the LFP whether their consumption was expressed as grams [AKR/J: F(1,682) = 2,601.13, P < 0.0001; SWR/J: F(1,633) = 9.68, P < 0.005] (Fig. 8) or kilocalories [AKR/J: F(1,682) = 5,259.97, P < 0.0001; SWR/J: F(1,633) = 187.34, P < 0.0001] (Fig. 9). Compared with SWR/J mice, AKR/J mice consumed a much greater proportion of total energy from the HFP diet [F(1,27) = 52.08, P < 0.0001], although this strain difference was the most reliable during the first week of the study (P < 0.01) (Fig. 10). Specifically, the proportion of HFP diet consumed by SWR/J mice increased over time, whereas that of AKR/J mice remained stable [strain × time interaction: F(24,643) = 2.24, P < 0.001].
|
|
|
At baseline, age-matched AKR/J mice weighed more than SWR/J mice
[F(1,26) = 45.06, P < 0.0001]. With a choice of
powdered diets, both strains significantly increased body weight over
time, but the AKR/J mice gained more than SWR/J mice [strain × time interaction: F(11,26) = 2.75, P < 0.05] (Fig.
11).
|
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND PROCEDURES
RESULTS
DISCUSSION
REFERENCES
|
|---|
The key finding of the present study is that the higher proportional intake of energy from fat by AKR/J compared with SWR/J mice generalized across diet paradigms, including those employing mixed macronutrients, liquid or powdered preparations, and saturated fat. Within-strain analyses showed that AKR/J mice reliably preferred the high-fat diet (expressed as grams or kilocalories) in all diet paradigms with the exception of the Lard group (g intake) in experiment 1. In SWR/J mice, macronutrient selection was differentially modified depending on the diet paradigm used. Specifically, SWR/J mice displayed a preference for the carbohydrate-protein diet (grams or kilocalories) in experiment 1. However, SWR/J mice consumed equivalent amounts of the liquid high- and low-fat diets; and when powdered high- and low-fat diets were employed, a preference for the high-fat diet was observed. Finally, a post hoc examination of results from all diet paradigms tested thus far in these two strains suggests that macronutrient selection in the SWR/J strain may be influenced by the amount of corn oil contained in the high-fat diet.
Experiment 1
Using two-choice semisolid diets we have replicated earlier observations of a significant strain difference (AKR/J vs. SWR/J) in self-selected proportional fat intake (27) and now have shown that this strain difference persists whether the fat source is vegetable shortening or lard.Diet preference or selection also was examined, within strain, for both gram and kilocalorie intakes. AKR/J mice reliably consumed more of the high- than low-fat diet when the fat source was vegetable shortening, when examined as grams or kilocalories. In the Lard group, an overall preference for fat was observed with kilocalorie intake but not with the analysis of grams. When expressed as kilocalories however, AKR/J mice in the Lard protocol initially did not prefer the fat-protein diet. However, 1 wk after diet presentation, intake of the fat-protein diet gradually increased and that of carbohydrate-protein decreased until a significant preference for the fat-protein diet emerged halfway through the study and continued thereafter. These results indicate that, for AKR/J mice, saturated fat influences both the pattern of acquisition and robustness of fat selection. This observation is in contrast to the preference of AKR/J mice for the Veg fat-protein diet (grams or kilocalories) from the day of initial presentation. These findings suggest that metabolic adaptations to lard may have occurred and contributed to the augmentation of fat ingestion over time (28) and that the orosensory properties of the lard-based fat-protein diet alone were insufficient to support a preference for this diet. Moreover, the orosensory properties of the food may have been aversive to AKR/J mice. In that case, our results may be similar to those obtained by Sclafani and Vigorito (26) in which rats increased their consumption of a Polycose solution over time despite the fact that it contained the bitter substance sucrose octaacetate. Thus, in the present study, the significant preference for the Lard-based fat-protein diet by AKR/J mice that appears ~2 wk into the study may reflect an increase in palatability conditioned by unknown postabsorptive factors (19).
Diet selection by SWR/J mice was influenced by the type of fat, i.e., this strain displayed a stronger preference for carbohydrate-protein and a weaker preference for fat-protein with lard as the fat source rather than vegetable shortening. Although either the orosensory or metabolic properties of lard may have been aversive to this strain, there is no apparent explanation for this response. This pattern of intake was observed with both the gram and kilocalorie analyses, although the SWR/J preference for carbohydrate-protein diet appears "stronger" with the gram analysis. Finally, although the regulation of protein intake can be an important factor affecting feeding behavior, these two diets contained the same amount of protein (22% of energy), thus precluding any conclusions about the effects of fat type on protein intake.
Although the amount of fat in the diet is known to affect body weight and body composition (8, 31), it is not clear whether dietary fat composition influences body weight and body fat accumulation in mice (6). In the present study, the body weight of AKR/J mice increased significantly more in both the Lard and Veg groups compared with chow; moreover AKR/J mice in the self-selection protocols were fatter than chow-fed animals regardless of fat type. These results are consistent with reports that in rats lard and corn oil do not have differential effects on total body fat or body weight (10-11). Although the self-selection diets had no effect on body weight of SWR/J mice, SWR/J mice in the Lard protocol were fatter than chow-fed mice and there was also a tendency for greater adiposity in the Veg group. Although the SWR/J strain is resistant to dietary obesity, it has been shown that these mice will increase body fat if dietary fat content is high enough, i.e., at least 45 kcal% (29). In the present study, SWR/J mice in the Veg and Lard protocols approached this level of dietary fat intake by voluntarily consuming as fat an overall average of 43 and 30 kcal%, respectively.
Experiment 2
The results obtained using the liquid composite diets indicate that the higher proportional fat intake by AKR/J mice compared with SWR/J mice is not as robust as that observed with solid or semisolid diets. In all previous paradigms tested with these mouse strains, the high-fat diet option contained a higher caloric density than the low- or no-fat options. It is known that food preferences can be conditioned on the basis of different caloric densities (3). The finding of a fat preference by AKR/J mice with isocaloric diet choices suggests that their preferential fat intake is not based on the caloric density of high-fat diets.The reason for the eventual decline in fat preference by AKR/J mice
during the liquid diet study is not apparent, although we hypothesized
that the liquid diets accelerated weight gain with the resulting
adiposity providing a negative feedback signal on fat intake. According
to previous studies, the addition of water to carbohydrate (24) or fat
(22) diets can induce overeating and obesity, e.g., liquid diets
increased weight gain in rats by ~0.7-1.4
g · animal
1 · day1
(22). However, in the present study, a post hoc analysis comparing body
weight gain over the first 20 days in both the liquid and powdered diet
experiments revealed a greater total weight gain with the powdered
diets for AKR/J (powder: 12.2 ± 0.6 g vs. liquid: 8.1 ± 0.5, P < 0.0001) but not SWR/J (powder:
6.8 ± 0.3 g vs. liquid: 5.7 ± 0.7) mice (age 7-8 wk).
(Note: mice in the liquid paradigm were 12 days older than mice in the
powdered diet experiment.) Therefore it does not appear that an
accelerated weight gain as a consequence of the liquid diets could
explain the decline in fat preference by AKR/J mice over the course of
the study.
Experiment 3
The powdered high- and low-fat diets used in this experiment replicated the strong fat preference of AKR/J mice as well as the higher proportional fat intake by AKR/J (0.85-0.92) compared with SWR/J (0.34-0.76) mice. However, this is the first diet paradigm in which a preference for fat by SWR/J mice has been demonstrated, i.e., SWR/J mice consumed more (grams or kilocalories) from the high- than the low-fat powdered diet.In an attempt to identify a possible source of the variation in
macronutrient selection by SWR/J mice, diet factors were examined across four experiments, including previous results obtained using the
three-choice macronutrient paradigm (27). We noted that preference for
high-fat diets in SWR/J mice appears to be augmented by the amount of
corn oil contained in the solid or semisolid high-fat diet options, but
not in the liquid diets (Table 3). For
example, the lowest proportional intake from the high-fat diet
(relative to total energy consumption) by SWR/J mice was 0.27 in the
three-choice macronutrient diet paradigm in which 100% of the fat was
provided in the form of vegetable shortening (Table 3). When the
high-fat diet option contained only 50% of calories from vegetable
shortening and another 50% from corn oil (powdered diets), the
proportion of high-fat intake by the SWR/J was higher, i.e., 0.67. Thus
it appears that the higher the corn oil content (or lower the vegetable
shortening content), the greater the proportion of high-fat diet
consumed by SWR/J mice. In contrast, the proportion of high-fat diet
intake by AKR/J mice was similar for all diet paradigms
(0.67-0.68), except for the powdered diets (0.88). It is also
possible that SWR/J mice have a greater preference for fat when it is
mixed with other macronutrients (4) because the lowest proportion of
fat intake by SWR/J mice was observed with the three-choice, separate
macronutrient diets (27).
|
Finally, the conclusion that the animals in these experiments selected diets solely on the basis of their generic nutrient content must be interpreted with caution (4) because the selection or consumption of diets may be attributed in large part to their individual sensory characteristics (5) and their postingestive and postabsorptive effects. Thus ideally a macronutrient-specific preference would require evidence that animals preferentially ingest the nutrient independent of its form in a particular diet. For example, the results of experiment 1 may be confounded by the contrasting textures of the semisolid diets, i.e, the choice between high-fat (oily, smooth paste) and low-fat (fine powder) diets. Texture variations in the diets were provided in experiments 2 (liquid) and 3 (granular/powder) where the two diet choices were more similar in physical characteristics. The strain difference in proportional high-fat diet intake was evident, although the phenotype was much weaker in the liquid diet test. A systematic examination of the role of specific sensory features in diet selection in these mouse strains was not attempted, thus more work is needed to resolve this issue. It should also be noted that casein was the only protein source used in the present experiments, therefore no conclusions or interpretations can be made about protein selection or the influence of protein sources on selection of other macronutrient-rich diets.
In summary, the present studies, together with an earlier report characterizing macronutrient selection in these two inbred mouse strains (27), have shown that the higher proportional fat intake of AKR/J compared with SWR/J mice generalizes to several diet paradigms, including those employing pure and mixed macronutrients; semisolid, powder, and liquid preparations; and saturated fat. This strain difference is due largely to the robust and reliable fat preference of the AKR/J mice. In contrast, macronutrient selection in SWR/J mice varied across paradigms, suggesting a differential response to some orosensory or postingestive factor(s).
Perspectives
An historic criticism of studies of diet selection has been that they lacked an examination of underlying mechanisms and physiological variables (21). Indeed the results of the present study are purely descriptive. However, the divergence in proportional fat intake characterized in these two inbred strains provides a valuable model for investigating the genetic basis of dietary fat preference. Earlier observations that the AKR/J and SWR/J strains differ in their sensitivity to dietary obesity, combined with the present results, thus support the potential relevance of this mouse model to human macronutrient selection and the development of obesity.| |
ACKNOWLEDGEMENTS |
|---|
We thank Dr. Julia Volaufova for assistance with the statistical analyses.
| |
FOOTNOTES |
|---|
This work was supported in part by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK-31988 and DK-45895 and by Knoll Pharmaceutical Company.
Current address for D. B. West: Parke-Davis Laboratory for Molecular Genetics, 1501 Harbor Bay Parkway, Alameda, CA 94502.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: B. K. Smith, Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, LA 70808 (E-mail: smithbk{at}mhs.pbrc.edu).
Received 22 June 1998; accepted in final form 21 May 1999.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND PROCEDURES
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Baker, B. J.,
and
D. A. Booth.
Effects of dl-fenfluramine on dextrin and casein intakes influenced by textural preferences.
Behav. Neurosci.
104:
153-159,
1990[Medline].
2.
Blundell, J. E.
Problems and processes underlying the control of food selection and nutrient intake.
In: Nutrition and the Brain, edited by R. J. Wurtman,
and J. J. Wurtman. New York: Raven, 1983, vol. 6, p. 163-221.
3.
Bolles, R. C.,
L. Hayward,
and
C. Crandall.
Conditioned taste preferences based on caloric density.
J. Exp. Psychol. Anim. Behav. Process.
7:
59-69,
1981[Medline].
4.
Booth, D. A.
Protein- and carbohydrate-specific cravings: neuroscience and sociology.
In: Chemical Senses: Appetite and Nutrition, edited by M. I. Friedman,
M. G. Tordoff,
and M. R. Kare. New York: Marcel Dekker, 1991, vol. 4, p. 260-276.
5.
Booth, D. A.
Sensory influences on food intake.
Nutr. Rev.
48:
71-77,
1990[Medline].
6.
Bourgeois, F.,
A. Alexiu,
and
D. Lemonnier.
Dietary-induced obesity: effect of dietary fats on adipose tissue cellularity in mice.
Br. J. Nutr.
49:
17-26,
1983[Medline].
7.
Cooling, J.,
and
J. Blundell.
Are high-fat and low-fat consumers distinct phenotypes? Differences in the subjective and behavioural response to energy and nutrient challenges.
Eur. J. Clin. Nutr.
52:
193-201,
1998[Medline].
8.
Fisher, J. O.,
and
L. L. Birch.
Fat preferences and fat consumption of 3- to 5-year-old children are related to parental adiposity.
J. Am. Diet. Assoc.
95:
759-764,
1995[Medline].
9.
Heitmann, B. L.,
L. Lissner,
T. I. Sorensen,
and
C. Bengtsson.
Dietary fat intake and weight gain in women genetically predisposed for obesity.
Am. J. Clin. Nutr.
61:
1213-1217,
1995
10.
Hill, J. O.,
D. Lin,
F. Yakubu,
and
J. C. Peters.
Development of dietary obesity in rats: influence of amount and composition of dietary fat.
Int. J. Obes.
16:
321-333,
1992.
11.
Hill, J. O.,
J. C. Peters,
D. Lin,
F. Yakubu,
H. Greene,
and
L. Swift.
Lipid accumulation and body fat distribution is influenced by type of dietary fat fed to rats.
Int. J. Obes.
17:
223-236,
1993.
12.
Johnson, S. L.,
L. McPhee,
and
L. L. Birch.
Conditioned preferences: young children prefer flavors associated with high dietary fat.
Physiol. Behav.
50:
1245-1251,
1991[Medline].
13.
McArthur, R. A.,
and
J. E. Blundell.
Dietary self-selection and intake of protein and energy is altered by the form of the diets.
Physiol. Behav.
38:
315-319,
1986[Medline].
14.
Macdiarmid, J. I.,
J. E. Cade,
and
J. E. Blundell.
High and low fat consumers, their macronutrient intake and body mass index: further analysis of the national diet and nutrition survey of British adults.
Eur. J. Clin. Nutr.
50:
505-512,
1996[Medline].
15.
McGee, C. D.,
and
C. E. Greenwood.
Effects of dietary fatty acid composition on macronutrient selection and synaptosomal fatty acid composition in rats.
J. Nutr.
119:
1561-1568,
1989.
16.
McGee, C. D.,
and
C. E. Greenwood.
Protein and carbohydrate selection respond to changes in dietary saturated fatty acids but not to changes in essential fatty acids.
Life Sci.
47:
67-76,
1990[Medline].
17.
Mela, D. J.
Eating behavior, food preferences and dietary intake in relation to obesity and body-weight status.
Proc. Nutr. Soc.
55:
803-816,
1996[Medline].
18.
Mullen, B. J.,
and
R. J. Martin.
Macronutrient selection in rats: effect of previous type and level of dietary fat.
J. Nutr.
120:
1418-1425,
1990.
19.
Naim, M.,
and
M. R. Kare.
Sensory and postingestional components of palatability in dietary obesity: an overview.
In: Chemical Senses: Appetite and Nutrition, edited by M. I. Friedman,
M. G. Tordoff,
and M. R. Kare. New York: Marcel Dekker, 1991, vol. 4, p. 109-126.
20.
National Research Council.
Nutrient Requirements of Laboratory Animals 10. Washington, DC: National Academy of Sciences, 1978.
21.
Overmann, S. R.
Dietary self-selection by animals.
Psychol. Bull.
83:
218-235,
1976[Medline].
22.
Ramirez, I.
Feeding a liquid diet increases energy intake, weight gain and body fat in rats.
J. Nutr.
117:
2127-2134,
1987.
23.
Reed, D. R.,
A. A. Bachmanov,
G. K. Beauchamp,
M. G. Tordoff,
and
R. A. Price.
Heritable variation in food preferences and their contribution to obesity.
Behav. Genet.
27:
373-387,
1997[Medline].
24.
Sclafani, A.
Carbohydrate-induced hyperphagia and obesity in the rat: effects of saccharide type, form, and taste.
Neurosci. Biobehav. Rev.
11:
155-162,
1987[Medline].
25.
Sclafani, A.
Starch and sugar tastes in rodents: an update.
Brain Res. Bull.
27:
383-386,
1991[Medline].
26.
Sclafani, A.,
and
M. Vigorito.
Effects of SOA and saccharin adulteration on Polycose preference in rats.
Neurosci. Biobehav. Rev.
11:
163-168,
1987[Medline].
27.
Smith, B. K.,
D. B. West,
and
D. A. York.
Carbohydrate versus fat intake: differing patterns of macronutrient selection in two inbred mouse strains.
Am. J. Physiol.
272 (Regulatory Integrative Comp. Physiol. 41):
R357-R362,
1997
28.
Warwick, Z. S.,
and
S. S. Schiffman.
Role of dietary fat in calorie intake and weight gain.
Neurosci. Biobehav. Rev.
16:
585-596,
1992[Medline].
29.
West, D. B.,
J. Waguespack,
and
S. McCollister.
Dietary obesity in the mouse: interaction of strain with diet composition.
Am. J. Physiol.
268 (Regulatory Integrative Comp. Physiol. 37):
R658-R665,
1995
30.
West, D. B.,
J. Waguespack,
B. York,
J. Goudey-Lefevre,
and
R. A. Price.
Genetics of dietary obesity in AKR/J X SWR/J mice: segregation of the trait and identification of a linked locus on chromosome 4.
Mamm. Genome
5:
546-522,
1994[Medline].
31.
West, D. B.,
and
B. A. York.
Dietary fat, genetic predisposition, and obesity: lessons from animal models.
Am. J. Clin. Nutr.
67, Suppl:
505S-512S,
1998[Abstract].
This article has been cited by other articles:
|
|
 |
|
  B. K. Smith, J. Volaufova, and D. B. West Increased flavor preference and lick activity for sucrose and corn oil in SWR/J vs. AKR/J mice Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2001; 281(2): R596 - R606. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. K. Smith, P. K. Andrews, and D. B. West Macronutrient diet selection in thirteen mouse strains Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2000; 278(4): R797 - R805. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
) and SWR/J (
) mice across 30-day study when fat-protein diet
contained either vegetable shortening
(A) or lard
(B). Values were derived from kcal
consumed from each diet during one 48-h period.
) and SWR/J (
) mice. Values were derived from kcal
consumed per 48 h. * P < 0.05 with Bonferroni.
