Abstract
To investigate whether dietary fat source and energy restriction interactively influence plasma leptin levels and its association of leptin with insulin action, rats were fed diets containing either fish, safflower oil, or beef tallow (20% wt/wt) for 10 weeks. Groups of rats consumed each diet ad libitum or at 85% or 70% of ad libitum energy intake in a design that held fat intake constant. Graded levels of energy restriction caused body weight to decrease (P < 0.001) differently according to the dietary fat provided. Plasma leptin concentrations were 60% higher (P < 0.05) in the groups fed fish oil and safflower oil ad libitum compared with those in the beef tallow group, despite smaller perirenal fat mass and fat cell size in the fish oil-fed animals. Energy restriction resulted in a 62% decrease (P < 0.05) in leptin levels in fish oil- and safflower oil-fed rats, whereas no changes were observed in beef tallow-fed animals. Plasma insulin levels were lower (P < 0.05) in the fish oil group fed ad libitum compared with those in the two other diet groups.▪ These data demonstrate a hyperleptinemic effect in animals consuming diets rich in polyunsaturated fatty acid, which can be normalized to the level of saturated fat consumption by mild energy restriction. Thus, dietary fatty acid composition, independent of adipose tissue mass, is an important determinant of circulating leptin level in diet-induced obesity.—Cha, M. C., and P. J. H. Jones. Dietary fat type and energy restriction interactively influence plasma leptin concentration in rats.
Highlights
To investigate whether dietary fat source and energy restriction interactively influence plasma leptin levels and its association of leptin with insulin action, rats were fed diets containing either fish, safflower oil, or beef tallow (20% wt/wt) for 10 weeks
We considered it would be of interest to investigate whether the previously reported correlation between insulin sensitivity and leptin level remained unchanged when dietary fatty acid composition was modified
Body weights at time of killing of all the animals in the ad libitum-fed groups and most of the animals in the 85% of energy intake groups were over 500 g, which is 60–100 g heavier than the chow-fed animals
Summary
Seventy-two male Sprague-Dawley rats (209 Ϯ 6.5 g) purchased from Charles River, Inc. (Quebec, Canada) were housed individually in stainless steel hanging cages with a 12-h light–dark cycle at 22Њ Ϯ 1ЊC environment. Animals within each fat group were either given free access to diets or were restricted to 85% or 70% of ad libitum daily intakes. Perirenal fat tissue adipocyte isolation and insulin binding analyses were performed according to methods of Olefsky and Reaven [18]. The cell suspension was incubated at 24ЊC for 45 min with 125Ilabeled pig insulin (New England Nuclear, DuPont Canada, QC; specific activity 80 Ci/g). Fat cell size was determined after extraction of depot lipid. Liver homogenate (100 l) was incubated in duplicate for 5 min at 37ЊC in a final volume of 1 ml containing 5 mm MgCl2, 120 mm NaCl, 7.5 mm KCl, 5 mm NaN3, 5 mm ATP, 12 mm Tris buffer at pH 7.4. The fatty acid composition of the experimental fats was determined by gas–liquid chromatography as described previously [21] (Table 2)
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