Grass-Fed and Grain-Fed Beef Fats Similarly Improve Metabolic Outcomes Compared with Pork Fat in Diet-Induced Obese Mice.

Abstract

Background: Although grass-fed and grain-fed production systems significantly affect the fatty acid composition of beef, evidence for distinct health outcomes remains limited despite widespread perceptions that grass-fed beef has health benefits.

Objective: We investigated whether chronic consumption of grass-fed versus grain-fed beef fat differentially affects metabolic outcomes compared with pork fat in a diet-induced obese mice.

Methods: Sixty male C57BL/6J mice were fed a low-fat diet (LFD, 10% kcal fat) or a high-fat diet (HFD, 45% kcal fat) containing rendered pork fat (HFD-P), grain-fed beef fat (HFD-GN), or grass-fed beef fat (HFD-GS) for 16 weeks. Metabolic assessments included glucose and insulin tolerance tests, circulating biochemical and inflammatory markers, tissue fatty acid composition, and insulin-stimulated Akt phosphorylation. Statistical analyses were performed using GraphPad Prism, with significance set at P < 0.05.

Results: Both beef fat groups similarly (P > 0.05) affected body weight, adiposity, glucose homeostasis, and insulin tolerance. Compared with HFD-P, both HFD-GS and HFD-GN reduced inguinal adiposity by ∼30% (P < 0.01) and improved glucose tolerance GTT AUC by ∼17% (P < 0.05), without differences in systemic insulin sensitivity as assessed by ITT, HOMA-IR, and insulin-stimulated Akt phosphorylation in adipose tissue (P > 0.05). Circulating inflammatory markers were lower with HFD-GS, with resistin concentrations ∼30% lower than HFD-GN and HFD-P and IL-6 concentrations ∼70% lower than HFD-P (P < 0.01). These responses coincided with distinct tissue fatty acid remodeling in HFD-GS mice, characterized by higher omega-3 polyunsaturated fatty acids, trans vaccenic acid, and rumenic acid, and a lower omega-6/omega-3 ratio in blood and adipose compared with HFD-GN and HFD-P.

Conclusions: Both beef fat sources similarly improved glucose tolerance and reduced adiposity compared with pork fat in HFD fed C57BL/6J mice. However, grass-fed beef fat may confer additional anti-inflammatory benefits associated with its distinct fatty acid composition.

Clinical trial registry number and website where it was obtained: N/A REGISTRY AND REGISTRY NUMBER FOR SYSTEMATIC REVIEWS OR META-ANALYSES: N/A.