Energy and Macronutrient Metabolism
Consumption of n-3 fatty acids (FA) decreases the risk for chronic diseases, including atherosclerosis and type 2 diabetes, and promotes thermogenic energy expenditure. There is a growing concern that dietary n-6 FA undermines the availability of n-3 FA suggesting that dietary n-6/n-3 FA ratio is a better determinant to predict metabolic outcomes than the total content of n-3 FA. This study aimed to test whether lowering the n-6/n-3 ratio in the solid fat would be effective in ameliorating the saturated fat-induced obesity and metabolic syndrome.
The obesity-prone C57BL/6 mice (n=8/group) were randomly assigned to any of three isocaloric diets that contain 45% of solid fat from either conventional butter (n-6/n-3 ratio=6), n-3 FA-enriched butter (n3Butter, n-6/n-3 ratio=1) or margarine (n-6/n-3 ratio=6), and fed for 10 weeks in comparison with chow-fed control mice. The changes in FA profile in erythrocytes were quantified by GC-MS, and lipoprotein composition in plasma were determined biweekly. The changes in body composition were determined by NMR minispec. Insulin sensitivity was evaluated by glucose and insulin tolerance test and HOMA-IR score. To determine the thermogenic potential, core-body temperature and heat release by IR camera were measured upon acute cold exposure (4°C). The brown-specific signature gene and protein profiles were determined upon cold for two days.
Results : Despite the similar n-3 FA content, n3Butter significantly increased the de novo synthesis of EPA ( >5-fold) and decreased arachidonic acid than margarine. Importantly, intracellular n-6/n-3 ratio in the liver, muscle, and white/brown adipose tissue were mirrored by dietary n-6/n-3 FA ratio. As a metabolic consequences, n3Butter intake substantially decreased 1) total and LDL-cholesterol levels, 2) visceral adiposity and adipose inflammation, and 3) glucose and insulin resistance compared to conventional butter or margarine. Notably, n3Butter intake showed higher thermogenic energy expenditure and brown/beige fat activation than isocaloric conventional butter or margarine.
Fortification and/or enrichment of n-3 FA in dairy products may be an alternative strategy to attenuate the obesity and metabolic complications mediated by chronic use of saturated fat.
Funding Sources :
NIH NIGMS P20 COBRE
Sunseo Omega Inc.