Insulin Regulates Energy Metabolism
A Healthy Metabolic System Supports Good Health
Carbohydrates, and fats are often called the high energy nutrients. Your body uses these nutrients as the primary sources of energy. To maintain good health, your body regulates the plasma levels of these nutrients to assure that you have adequate amounts of nutrients to meet your body's metabolic needs. Excessive or insufficient amounts of these nutrients are incompatible with good health. Life itself may cease if they are not adequately regulated. Insulin is the primary hormone that manages the distribution and utilization of these high energy nutrients. The influence of insulin is pronounced at three critical sites: the muscles, the liver and the fat cells.
The primary task for insulin is to maintain a steady-state level of blood sugar (homeostatic regulation of plasma glucose). To meet this goal, insulin stimulates the uptake of glucose by the muscles and other organs when the blood level of glucose is elevated, and activates glucose release into the blood when the plasma blood level is lowered. The muscles, liver and fat cells are the key players in the homeostatic regulation of plasma glucose. If high energy nutrients are not adequately managed, numerous adverse events can follow, and they range from obesity to type 2 diabetes, and from ischemic vascular disease to sudden death.
Stimulation of Insulin Release
Glucose is the nutrient that activates the release of insulin from the pancreas. When plasma glucose (blood sugar) rises the beta cells in the pancreas are stimulated to release insulin. The released insulin then stimulates the uptake of glucose by the muscles and other tissues. When glucose level goes down, insulin level will also go down. This coupled action of glucose and insulin works very well as long as this control system is not impaired. Consuming large amounts of refined foods, particularly refined carbohydrates can impair this glucose control system by making the system less sensitive. Foods that increase insulin resistance such as trans fats can also impair the proper functioning of this control system. In the presence of refined carbs or insulin resistance-inducing foods, plasma level of insulin would go up. This change is bad because sustained elevation in the plasma level of insulin supports fat storage and obesity.
Energy Utilization by the Muscles
Muscles are the biggest energy users in the body. Muscles can use both carbohydrate and fats (fatty acids) as metabolic fuels. Insulin plays an important role in energy utilization by the muscles. In the case of carbohydrate metabolism (glucose metabolism) Insulin plays critical role in the skeletal muscles (but not the heart muscle) because it helps to transport glucose into the muscle cells making it available for metabolism. The available type of metabolic fuel (fatty acids or carbohydrates) determines which metabolite is used for energy by the muscles.
If more glucose is transported into the muscle cells than is needed immediately for energy, glucose is stored in the muscle as glycogen. The synthesis of glycogen (a chain of glucose) is supported by insulin. This glycogen becomes an important source of metabolic fuel for the muscle if the supply of metabolic fuels from the blood becomes inadequate.
Nutrient Utilization by the Liver
Insulin has profound effects on the utilization of high energy nutrients in the liver. In sharp contrast to the muscles where metabolic fuels are burned, the liver can synthesize, store and release these nutrients so that they can be utilized by other organs and tissues. Insulin supports the synthesis and storage of these high energy metabolic fuels in the liver. Energy can be stored as glycogen (a chain of glucose). These high energy foods can also be converted to fat in the liver in the presence of insulin. The stored energy fuels in the liver can also be released into the blood stream to maintain adequate nutrient levels for various organs in the body.
The liver releases glucose into the blood stream when the blood glucose level goes down. This glucose release is very important for the homeostatic regulation of blood glucose. This glucose may come from the breakdown of stored sugar in the form of glycogen. It can also come from glucose that is produced by a process called gluconeogenesis. Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources. In this process, amino acids are typically converted to glucose.
Fatty acids can be released from the liver into the blood stream. These fatty acids are transported to the fat cells and reassembled as fats (triglycerides). Fats are a compact form of stored energy compared to glycogen. Consequently, fats have less mass compared to glycogen for any given amount of stored energy. This storage of fat in the fat cells is supported by Insulin .
The Fat Cells
insulin facilitates the synthesis and storage of fat in the fat cells. The word “facilitate” is used when describing the action of insulin in the fat cells because insulin does not directly catalyze or stimulate the biochemical reactions for the synthesis of fat but it has a profound effect on the enzyme that breaks down fat to fatty acids. Fats (triglycerides) must be broken down before they can go through the blood vessels to enter the blood stream. Insulin inhibits the activity of the enzyme that stimulate the break-down of fat in the fat cells. Agents such as epinephrine (adrenalin) and norepinephrine (noradrenaline) stimulate the breakdown of fats and the release of fatty acids from the fat cells.
Hormone sensitive lipase (HSL) is the primary enzyme that is activated to break-down fat. Glucagon, epinephrine and epinephrine can stimulate this enzyme, and this leads to loss of body fat. Insulin inhibits JSL and prevents or slows down the break-down of fat. Consequently, increased plasma levels of insulin supports fat storage. This helps to move some of the high energy nutrients from blood so that plasma levels of these high energy nutrients are maintained at appropriate levels. The potential adverse effect of this fat storage is that it can promote obesity.
Lowered plasma level of insulin has significant effects on the metabolism of fat in the fat cells. In conditions where the plasma level of the high energy nutrients is low, fatty acids are released into the blood from the fat cells. Insulin plays an important role in this release of fatty acids. Plasma level of insulin is lowered in this condition of lowered plasma levels of high energy nutrients. The decline in the plasma level of insulin facilitates the breakdown of fat (to glycerol and fatty acids) and the release of fatty acids from the fat cells. The released fatty acids can then be carried to the muscles where they are burned. Body fat reduction would result from this lowered plasma level of insulin.
Insulin and Body Weight Control
Since elevated plasma level of insulin supports body fat synthesis and storage, some diet plans try to lose body fat by staying on dietary protocols that prevent insulin level from going up. Low Carb Diet and Glycemic Index Dieting are two effective dietary plans that apply this approach for controlling body weight.
Carbohydrates are the primary nutrients that cause the release of insulin. Refined carbohydrates are the most potent carbs that release insulin. Low Carb Diet tries to control insulin by reducing the amount of carb that is consumed; whereas, Glycemic Index Dieting achieves a similar goal by refraining from consuming foods with high glycemic index values. These high glycemic index foods are mostly refined carbs (bad carbs).