Chapter 7 Metabolic syndrome

Chapter overview Introduction Definition and prevalence Causal factors Characteristic abnormalities Physical activity and fitness Exercise and postprandial events Prevention Physical activity as therapy? Summary

In combination, risk factors are powerful predictors of CHD

Defining characteristics of the metabolic syndrome Central obesity; raised triglycerides; low HDL-cholesterol; raised BP; raised fasting plasma glucose.

Associated abnormalities Diabetes or impaired glucose tolerance; hyperinsulinaemia; atherogenic dyslipidaemia; exaggerated postprandial lipaemia; high levels of markers for inflammation; microalbinuria; high uric acid; non-alcoholic fatty liver disease; endothelial dysfunction.

Prevalence Normal-weight people Range 8–24% in men, 7–43% in women Typically 20–25% in developed countries; obese individuals – around one-third; highly age-dependent, but evident in obese children; genetic predisposition in some ethnic groups.

Influences of insulin on carbohydrate and fat metabolism Mediates glucose uptake and metabolism in muscle and adipose tissue; suppresses glucose production by the liver and kidney; promotes uptake and storage of fatty acids in adipose tissue; inhibits mobilization of fatty acids from adipose tissue; decreases secretion of very low-density lipoproteins from the liver.

Insulin promotes lipid storage and synthesis

Why postprandial studies? Insulin coordinates metabolism during the hours after a meal, so the consequences of resistance to its effects on lipid metabolism are seen most clearly during the postprandial period. People spend the majority of their lives in the postprandial state. When triglycerides are high: blood has an increased propensity to clot; there are detrimental effects on endothelial function; systemic inflammation is increased.

Postprandial responses exaggerated in visceral obesity

Metabolic syndrome more common in inactive people

Strength and fitness both inversely associated with the metabolic syndrome

Prospective study: incidence of syndrome higher in low-fit people

Triglyceride responses to a fat-rich meal lower in endurance-trained men

Influence of prior exercise on postprandial responses in lean and centrally obese men

‘Trading’ intensity for duration: triglyceride responses to a high-fat mixed meal

Summary I There is a high prevalence of the metabolic syndrome in developed countries. It confers high risk for type 2 diabetes and CVD. Abnormalities include: hyperinsulinaemia; high triglycerides; low HDL-cholesterol; obesity, particularly abdominal obesity; endothelial dysfunction; systemic inflammation.

Summary II The defining causal feature is controversial. Inactivity, low fitness and sedentary behaviours are associated with the syndrome. Physical activity has a preventive – and probably a therapeutic – role in ameliorating multiple syndrome features. Postprandial lipid and non-lipid disturbances are attenuated by physical activity.