ABSTRACT
Insulin is a hormone produced by the endocrine pancreas, in particular by pancreatic β-cells, in response to hyperglycemia. Under normal conditions, muscle cells and fat cells are equipped with insulin receptors. After a meal, pancreatic β-cells increase insulin secretion, insulin binds to its receptors in muscle and adipose tissue with migration of glucose transport glucose 4 (GLUT4) channels, quiescent in the cellular cytoplasm, to the surface of the membrane cell, allowing glucose entrance in the cell. Also, the liver is equipped with insulin receptors: after the meal, insulin binds to hepatic receptors and with a cascade of signals inhibits glycogenolysis in favor of glycogenesis. Moreover, insulin links to its receptors in liver 224cause opening of glucose transport glucose 2 channels (GLUT2), allowing glucose to enter the hepatic cell. Insulin resistance is a condition characterized by a reduced capacity of muscular, adipose, and liver cells to respond to insulin; these cells become less sensitive to the action of insulin, making more insulin needed to perform the same actions. In the initial stages, the pancreas produces more insulin to maintain normal blood glucose levels with greater work by the β-cells and hyperinsulinemia. Over time, the pancreas begins to fail to compensate for the greater need of insulin due to insulin resistance; when this happens, glycemia begins to rise, initially after meals, and then even fasting. This constant increase in fasting blood sugar can, over the years, lead to type 2 diabetes mellitus. However, insulin resistance does not only cause diabetes, because hyperinsulinemia is also considered a predictor of future cardiovascular events. 1,2 Insulin resistance, in fact, can increase fibrinogen in the blood and is closely associated with hypertension in the obese and not obese. 3 For this reason, prevention is certainly important; since insulin resistance is almost always linked to excessive weight, the first intervention should be an appropriate lifestyle. Lifestyle changes require the patient to be educated to follow a proper diet, in order to obtain a correction of excess body weight. An appropriate nutritional plan is based on the model of the Mediterranean diet and provides a total fat intake of less than 30%; a supply of saturated fatty acids below 10%; a supply of fibers, half soluble, exceeding 15 g/1000 kcal; a carbohydrate intake of 45%–60%; and proteins equal to 15%–20%. Patients should limit saturated fat intake to less than 7% of daily caloric needs; monounsaturated fatty acids, such as olive oil and other vegetable oils, are recommended. 4 Patient should also be encouraged to increase physical activity and, in particular, to practice aerobic activity for at least 30–40 minutes, 3–4 times a week. If the patient is a smoker, he or she should be encouraged to quit. In addition to this, it is also important to address all cardiovascular risk factors (dyslipidemia, hyperglycemia, hypertension, smoking). Following an adequate healthy lifestyle, however, is not always easy, and nutraceuticals can be helpful to patients for this reason. The science of nutraceuticals is constantly evolving; different substances have shown a favorable effect in controlling lipid profile, glycemia, hypertension, insulin resistance, and metabolic parameters. 5,6 In the next pages, we will describe the main nutraceuticals with evidence of a certain action on glycemia and insulin resistance. For the description of how various nutraceuticals act, please see Table 13.1 and Figures 13.1–13.7. For a description of their chemical formula, see Table 13.2.
