Metabolic syndrome is characterised by abdominal adiposity, insulin resistance and blood lipid changes, as well as increased systemic oxidative stress and inflammation. The cause of metabolic syndrome is unclear, but evidence suggests that low quality, high-calorie diets are associated with its development. The abnormalities seen in sufferers of metabolic syndrome can increase the risk of a number of diseases including cardiovascular disease and diabetes. Non-alcoholic fatty liver disease (NAFLD), and its more severe form non-alcoholic steatohepatitis (NASH), may also be linked to the metabolic syndrome because fuel utilisation is impaired and this results in the accumulation of triglycerides in the liver tissue. Non-alcoholic fatty liver disease is a spectrum of similar disorders with NASH being considered the most severe, although all of the variations can lead to cirrhosis, hepatocellular carcinoma, liver disease and death.
Evidence suggests that diet is an important factor in the development of NAFLD, with insulin resistance and glucose intolerance being central to the theory. Diets high in fructose may cause insulin resistance, and the increase in consumption of dietary fructose over recent decades mirrors the rise in obesity in Western nations. Once peripheral insulin resistance has developed, plasma fasting insulin levels rise, which alters fuel substrate utilisation. High intakes of carbohydrate cannot be processed by the muscle because of their insensitivity to insulin, and so glucose is shunted to the adipose tissue and the liver. In the adipose tissue accumulation of triglycerides results from the overabundance of glucose and inflammation results. In the liver glucose is metabolised to fatty acids and triglycerides via de novo lipogenesis, a process which is stimulated by insulin. The triglycerides then accumulate along with cholesterol esters causing NAFLD and lipoprotein abnormalities..
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