Cardio-Metabolic Effects of High-Fat Diets and Their Underlying Mechanisms-A Narrative Review

Abstract

The majority of the epidemiological evidence over the past few decades has linked high intake of fats, especially saturated fats, to increased risk of diabetes and cardiovascular disease. However, findings of some recent studies (e.g., the PURE study) have contested this association. High saturated fat diets (HFD) have been widely used in rodent research to study the mechanism of insulin resistance and metabolic syndrome. Two separate but somewhat overlapping models-the diacylglycerol (DAG) model and the ceramide model-have emerged to explain the development of insulin resistance. Studies have shown that lipid deposition in tissues such as muscle and liver inhibit insulin signaling via the toxic molecules DAG and ceramide. DAGs activate protein kinase C that inhibit insulin-PI3K-Akt signaling by phosphorylating serine residues on insulin receptor substrate (IRS). Ceramides are sphingolipids with variable acyl group chain length and activate protein phosphatase 2A that dephosphorylates Akt to block insulin signaling. In adipose tissue, obesity leads to infiltration of macrophages that secrete pro-inflammatory cytokines that inhibit insulin signaling by phosphorylating serine residues of IRS proteins. For cardiovascular disease, studies in humans in the 1950s and 1960s linked high saturated fat intake with atherosclerosis and coronary artery disease. More recently, trials involving Mediterranean diet (e.g., PREDIMED study) have indicated that healthy monounsaturated fats are more effective in preventing cardiovascular mortality and coronary artery disease than are low-fat, low-cholesterol diets. Antioxidant and anti-inflammatory effects of Mediterranean diets are potential mediators of these benefits.

Keywords: cardiovascular disease; diabetes; high-fat diet; insulin resistance; metabolism; mice; obesity; saturated fatty acids.

Figure 1

Cardiometabolic phenotype of HFD-fed mice. HFpEF: Heart failure with preserved ejection fraction.

Figure 2

Molecular mechanisms of insulin actions and insulin resistance. DAG: diacylglycerol; FOXO: Forkhead box protein O; GLUT4: glucose transporter type 4; GSK3ß: glycogen synthase kinase 3 beta; IKKß: inhibitor of nuclear factor kappa-B kinase subunit beta; IR: insulin receptor; IRS: insulin receptor substrate; JNK: c-Jun N-terminal kinases; MAPK: mitogen-activated protein kinase; PDK: phosphoinositide-dependent kinase; PI3K: phosphoinositide 3-kinases; PIP₃: phosphatidylinositol (3,4,5)-trisphosphate; PKC: protein kinase C; PP2A: protein phosphatase 2A; S6K: ribosomal protein S6 kinase; SOCS: suppressor of cytokine signaling; SREBP1: sterol regulatory element-binding protein 1.