INRA, Unité de Nutrition Humaine, Clermont Ferrand/Theix, 63122 Saint-Genès-Champanelle, France, Veterinary Faculty, Norwida Str. 31, 50375 Wroclaw, Poland
The metabolic syndrome is a cluster of common pathologies: abdominal obesity linked to an excess of visceral fat, insulin resistance, dyslipidemia and hypertension. This syndrome is occurring at epidemic rates, with dramatic consequences for human health worldwide, and appears to have emerged largely from changes in our diet and reduced physical activity. An important but not well-appreciated dietary change has been the substantial increase in fructose intake, which appears to be an important causative factor in the metabolic syndrome. There is also experimental and clinical evidence that the amount of magnesium in the western diet is insufficient to meet individual needs and that magnesium deficiency may contribute to insulin resistance. In recent years, several studies have been published that implicate subclinical chronic inflammation as an important pathogenic factor in the development of metabolic syndrome. Pro-inflammatory molecules produced by adipose tissue have been implicated in the development of insulin resistance. The present review will discuss experimental evidence showing that the metabolic syndrome, high fructose intake and low magnesium diet may all be linked to the inflammatory response. In many ways, fructose-fed rats display the changes observed in the metabolic syndrome and recent studies indicate that high-fructose feeding is associated with NADPH oxidase and renin-angiotensin activation. The production of reactive oxygen species results in the initiation and development of insulin resistance, hyperlipemia and high blood pressure in this model. In this rat model, a few days of experimental magnesium deficiency produces a clinical inflammatory syndrome characterized by leukocyte and macrophage activation, release of inflammatory cytokines, appearance of the acute phase proteins and excessive production of free radicals. Because magnesium acts as a natural calcium antagonist, the molecular basis for the inflammatory response is probably the result of a modulation of the intracellular calcium concentration. Potential mechanisms include the priming of phagocytic cells, the opening of calcium channels, activation of N-methyl-D-aspartate (NMDA) receptors, the activation of nuclear factor-kappaB (NFkB) and activation of the renin-angiotensin system. Since magnesium deficiency has a pro-inflammatory effect, the expected consequence would be an increased risk of developing insulin resistance when magnesium deficiency is combined with a high-fructose diet. Accordingly, magnesium deficiency combined with a high-fructose diet induces insulin resistance, hypertension, dyslipidemia, endothelial activation and prothrombic changes in combination with the upregulation of markers of inflammation and oxidative stress.