David B. West

Effects of conjugated linoleic acid on body fat and energy metabolism in the mouse

Conjugated linoleic acid (CLA) is a naturally occurring group of dienoic derivatives of linoleic acid found in the fat of beef and other ruminants. CLA is reported to have effects on both tumor development and body fat in animal models. To further characterize the metabolic effects of CLA, male AKR/J mice were fed a high-fat (45 kcal%) or low-fat (15 kcal%) diet with or without CLA (2.46 mg/kcal; 1.2 and 1.0% by weight in high- and low-fat diets, respectively) for 6 wk. CLA significantly reduced energy intake, growth rate, adipose depot weight, and carcass lipid and protein content independent of diet composition. Overall, the reduction of adipose depot weight ranged from 43 to 88%, with the retroperitoneal depot most sensitive to CLA. CLA significantly increased metabolic rate and decreased the nighttime respiratory quotient. These findings demonstrate that CLA reduces body fat by several mechanisms, including a reduced energy intake, increased metabolic rate, and a shift in the nocturnal fuel mix.

Conjugated linoleic acid rapidly reduces body fat content in mice without affecting energy intake

Recent reports have demonstrated that conjugated linoleic acid (CLA) has effects on body fat accumulation. In our previous work, CLA reduced body fat accumulation in mice fed either a high-fat or low-fat diet. Although CLA feeding reduced energy intake, the results suggested that some of the metabolic effects were not a consequence of the reduced food intake. We therefore undertook a study to determine a dose of CLA that would have effects on body composition without affecting energy intake. Five doses of CLA (0.0, 0.25, 0.50, 0.75, and 1.0% by weight) were studied in AKR/J male mice ( n = 12/group; age, 39 days) maintained on a high-fat diet (%fat 45 kcal). Energy intake was not suppressed by any CLA dose. Body fat was significantly lower in the 0.50, 0.75, and 1.0% CLA groups compared with controls. The retroperitoneal depot was most sensitive to the effects of CLA, whereas the epididymal depot was relatively resistant. Higher doses of CLA also significantly increased carcass protein content. A time-course study of the effects of 1% CLA on body composition showed reductions in fat pad weights within 2 wk and continued throughout 12 wk of CLA feeding. In conclusion, CLA feeding produces a rapid, marked decrease in fat accumulation, and an increase in protein accumulation, at relatively low doses without any major effects on food intake.Recent reports have demonstrated that conjugated linoleic acid (CLA) has effects on body fat accumulation. In our previous work, CLA reduced body fat accumulation in mice fed either a high-fat or low-fat diet. Although CLA feeding reduced energy intake, the results suggested that some of the metabolic effects were not a consequence of the reduced food intake. We therefore undertook a study to determine a dose of CLA that would have effects on body composition without affecting energy intake. Five doses of CLA (0.0, 0.25, 0.50, 0.75, and 1.0% by weight) were studied in AKR/J male mice (n = 12/group; age, 39 days) maintained on a high-fat diet (%fat 45 kcal). Energy intake was not suppressed by any CLA dose. Body fat was significantly lower in the 0.50, 0.75, and 1.0% CLA groups compared with controls. The retroperitoneal depot was most sensitive to the effects of CLA, whereas the epididymal depot was relatively resistant. Higher doses of CLA also significantly increased carcass protein content. A time-course study of the effects of 1% CLA on body composition showed reductions in fat pad weights within 2 wk and continued throughout 12 wk of CLA feeding. In conclusion, CLA feeding produces a rapid, marked decrease in fat accumulation, and an increase in protein accumulation, at relatively low doses without any major effects on food intake.

Dietary obesity linked to genetic loci on chromosomes 9 and 15 in a polygenic mouse model.

Loci linked to sensitivity to dietary obesity were identified by Quantitative Trait Locus (QTL) analysis of two mapping populations derived from a cross between AKR/J and SWR/J mice. AKR/J mice are sensitive to dietary obesity when fed a high fat diet while SWR/J mice are resistant. Intercrosses between these strains segregate the phenotype of sensitivity to dietary obesity. Using an F2 mapping population of 931 male mice we found significant linkage with a QTL on chromosome 9 (Likelihood of the Odds [LOD] ratio of 4.85) and another QTL on chromosome 15 (LOD = 3.93). The presence of a QTL on chromosome 15 was confirmed in a separate mapping population of 375 male F1 x SWR/J mice (LOD = 3.82). These two loci are designated dietary obese 2 (Do2) and dietary obese 3 (Do3) for the chromosome 9 and 15 loci, respectively. Both of these chromosomal regions contain candidate genes which may contribute to variation in the phenotype. These loci also exert a significant control over individual adipose depot weights.

Genetics of dietary obesity in AKR/JxSWR/J mice: segregation of the trait and identification of a linked locus on Chromosome 4

We describe a new multiple gene mouse model of differential sensitivity to dietary obesity that provides a tool for dissecting the genetic basis for body composition and obesity. AKR/J and SWR/J male mice, as well as male progeny of intercrosses between these strains, were fed a high-fat diet for 12 weeks beginning at 5 weeks of age. Body weight and energy intake were assessed weekly. At the conclusion of the dietary manipulation, an adiposity index was calculated by dividing the weight of seven dissected adipose depots by the carcass weight. AKR/J mice had approximately sixfold greater adiposity than SWR/J mice. Examination of the segregation of the adiposity trait in the progeny of crosses between these strains indicates that the trait is determined by a minimum of one to four genetic loci and that there is significant dominance of the AKR/J genotype. A preliminary analysis with markers linked to the known mouse obesity genes ob, db, tub, and fat showed no linkage with these loci. However, a quantitative trait locus was found that maps distal to the db gene on Chromosome (Chr) 4. This locus has been designated dietary obese 1 or Do1.

Reliability and Validity of a Macronutrient Self-Selection Paradigm and a Food Preference Questionnaire

Our laboratory has developed a macronutrient self-selection paradigm (MSSP) designed to vary fat content significantly and systematically with sugar, complex carbohydrates, and protein content in a battery of foods in which fat is commonly consumed in the American diet. We have also developed a food preference questionnaire (FPQ) according to an identical design but using a list of foods mutually exclusive of those presented for selection and intake in the MSSP. Men were tested twice on both instruments, with a 4-week interval between tests. It was determined that the MSSP has strong test-retest reliability for overall fat (r = 0.91) and other macronutrient intake and total caloric intake. In addition, hunger and fullness ratings were reproducible, and fat preferences (r = 0.99) and hedonic responses to foods listed on the FPQ were highly consistent across trials. This study also demonstrated that the MSSP is a valid instrument with respect to the mens reports of habitual intake of fat (r = 0.80) and total carbohydrates on the Block food questionnaire (FQ). In addition, mens fat preferences on the FPQ were validated with respect to overall fat (r = 0.86) and total caloric intake in the MSSP and fat intake (r = 0.83) reported on the Block FQ. The MSSP also has the capability to detect a wide range of fat intake (3.06-50.35% among the present subjects), indicating that this instrument can identify individuals who differ markedly in fat intake or could detect changes in fat preference within subjects. In addition, this paradigm detected a large range of sugar and total caloric intake. It is anticipated that the use of these laboratory tools can enhance our understanding of the relationship between dietary fat intake and obesity.

Sensitivity to dietary obesity linked to a locus on Chromosome 15 in a CAST/Ei × C57BL/6J F2 intercross

Details of a new model of diet-dependent polygenic obesity are presented. CAST/Ei (Mus m. castaneus) mice remain lean after 12 weeks on a high-fat (32 kcal% fat) diet, while C57BL/ 6J mice become obese. The genes responsible for the obesity segregate in an F2 population derived from an intercross between CAST/Ei and C57BL/6J mice. Quantitative trait analysis, with simple sequence length polymorphisms (SSLPs) at loci previously linked to rodent obesities, identified a quantitative trait locus (QTL) on Chromosome (Chr) 15, accounting for approximately 9% of the variance in adiposity and 14% of the variance in mesenteric depot size. This locus appears to be at the same location as the dietary obesity-3 (Do3) locus controlling body fat content, which was previously identified in an F2 population derived from an SWR/J × AKR/J cross. This is also at the same location as the multigenic obesity-4 (Mob4) locus found in BSB mice, which display spontaneous polygenic obesity. Suggestive linkage also was found at loci close to the single gene mutations Ay on Chr 2 and tub on Chr 7.

Inherited non-autosomal effects on body fat in F2 mice derived from an AKR/J x SWR/J cross.

Abstract. In this study we describe the contribution of matrilineal and patrilineal effects on the adiposity, body weight, and on the weights of individual fat pads in F2 male mice derived from an SWR/J × AKR/J cross. AKR/J mice become obese after 12 weeks on a high-fat diet, whereas SWR/J mice remain relatively lean. Here we report that mice with AKR maternal and AKR paternal grandmothers have significantly larger epidydimal and retroperitoneal fat pads than those with SWR maternal and paternal grandmothers. However, grandparental strain had no effect on the overall adiposity (AI) or the weights of the inguinal, subcutaneous or mesenteric fat pads. The strain of the paternal grandparents had a small but significant effect on body weight. These effects can be attributed to in utero effects, imprinting effects, cytoplasmic and/or Y chromosome transmission of factors controlling body fat. We also describe the presence of a quantitative trait locus (QTL) on Chromosome X, close to DXMit174, which is linked to adiposity, body weight, and to the weights of the individual fat depots. However, this QTL is not responsible for the grandparental strain effects described above.

Gene-environment interaction: a significant diet-dependent obesity locus demonstrated in a congenic segment on mouse chromosome 7.

Abstract. We have previously reported suggestive evidence for a locus on Chromosome (Chr) 7 that affects adiposity in F2 mice from a CAST/Ei × C57BL/6J intercross fed a high-fat diet. Here we characterize the effect of a high-fat (32.6 Kcal% fat) diet on male and female congenic mice with a C57BL/6J background and a CAST/Ei-derived segment on Chr 7. Adiposity index (AI) and weights of certain fat pads were approximately 50% lower in both male and female congenic mice than in control C57BL/6J mice, and carcass fat content was significantly reduced. The reduction of fat depot weights was not seen, however, in congenic animals fed a low-fat chow diet (12 Kcal% fat).The congenic segment is approximately 25 cM in length, extending from D7Mit213 to D7Mit41, and includes the tub, Ucp2, and Ucp3, genes, all of which are candidate genes for this effect. Some polymorphisms have been found on comparing c-DNA sequences of the Ucp2 gene from C57BL/6J and CAST/Ei mice. These results suggest that one or more genes present in the congenic segment modulate the susceptibility to fat deposition on feeding a high-fat diet.We were unable to show any significant difference between the energy intakes of the congenic and the control C57BL/6J mice on the high-fat diet. Also, measurements of energy expenditure in male mice at 6 weeks of age, during the first 2 weeks of exposure to the high-fat diet, failed to show any differences between control and congenic animals.

Early-onset repeated dieting reduces food intake and body weight but not adiposity in dietary-obese female rats.

As dieting behavior and attempts at weight loss are becoming increasingly common in adolescent girls, we wished to determine whether early-onset repeated dieting influenced the development of obesity and its metabolic correlates. Female rats were fed a high-fat diet and subjected to six cycles of dieting and regain, beginning in the peripubertal period. Although dieted rats weighted less than nondieted high-fat fed controls at the completion of the sixth cycle, body composition analysis revealed that the two groups were equally obese. Cumulative caloric intake was less in dieted rats, suggesting that the pattern of consumption promoted by dieting helped to establish the obesity. Resting metabolic rate did not differ between the two groups. These data suggest that although early-onset repeated dieting may result in reduced body weight, the eventual level of adiposity may be unknowingly elevated, potentially leading to long-term health risks.

Divergence in proportional fat intake in AKR/J and SWR/J mice endures across diet paradigms.

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).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).