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With the popularity of low-carb diets today, most of us have at one time or another considered cutting carbs. In this series of articles we have discussed 'low-carbing' and whether or not it's right for everyone.
In this article we're going to talk about carbohydrates and how they are stored in the body. Does a large supply of excess carbs make us fat?
Many people believe that only dietary fat will lead to body fat. False! Actually, eating more calories than your body needs to perform daily activities and daily metabolism is what causes body fat. It is as simple as putting 20 gallons of gas in a 15 gallon gas tank.....the excess must go somewhere. In the case of human nutrition, the excess is stored as fat.
Just as excess protein can be stored as body fat, excess carbohydrate can be stored as body fat. Unfortunately for the American public, our consumption of simple carbohydrates has skyrocketed over the last ten years! Too many of us took the popularity of the low-fat and fat-free diets as an excuse to fill up on empty carbo-calories. After all, it's okay to eat the entire package of licorice since it's all fat free....right? Again, False!
Carbohydrates that the body cannot use are stored as body fat, plain and simple. Carbohydrates usually are ingested in the forms of polysaccharides (starches), disaccharides (sucrose and lactose) and monosaccharides (glucose and fructose). Essentially what occurs in the digestive process is a breakdown of the polysaccharides and disaccharides to the monosaccharides. The primary site of digestion is the small intestine, where the monosaccharides are then absorbed into the blood. Of the three monosaccharides, glucose is of most importance to human physiology. This is called blood sugar. Fructose and galactose are converted to blood glucose either in the intestinal wall or the liver.
A high-carbohydrate meal will lead to a rapid increase in the blood sugar level, usually within an hour. Naturally, the higher the food is on the glycemic index (refined sugars), the higher the blood sugar level will rise. The maintenance of a normal blood sugar level is very important for proper metabolism. The human body regulates blood sugar levels by a hormone called insulin. The rises in blood sugar levels stimulate the pancreas to secrete the hormone insulin into the blood. Insulin then facilitates the uptake and utilization of blood sugar by various tissues in the body, most notably the muscles and adipose tissue.
The fate of blood sugar is dependent on many factors, with exercise being one of the most important.
1) Blood sugar may be used for energy, particular
ly by the brain and other parts of the nervous system.
2) Blood sugar may be converted to either liver or muscle glycogen. Liver glycogen may then be later converted to blood sugar. Muscle glycogen is, for the most part, locked into the muscle cell once it enters, where it is converted to energy.
3) Blood sugar may be converted to and stored as fat in the adipose tissue. This situation occurs when the dietary carbohydrate, in combination with caloric intake of other nutrients, exceeds the energy demands of the body, and the storage capacity of the liver and muscles for glycogen.
4) Some blood sugar also may be excreted in the urine if excessive amounts occur in the blood, because of rapid ingestion of simple sugars.
So, what happens if we don't consume enough carbohydrates? Because the carbohydrate stores in the body are rather limited, and because blood sugar is normally essential for optimal functioning of the central nervous system, it is important to be able to produce blood sugar or glucose internally if the stores are depleted by starvation or a zero-carbohydrate diet. This process is called gluconeogenesis, meaning the formation of glucose. In this process, protein is converted to glucose, and fat is converted to glucose by breaking down glycerol in the liver. The by-products of carbohydrate metabolism, lactate and pyruvate, may also be converted back to glucose in the liver.
With this understanding of how carbohydrate is metabolized in the body, it is clear that low-carb or no-carb diets may lead to decreased levels of energy.
Low-carb diets, however, have been proven to take off the weight. In some cases, weight loss has been dramatic when the subjects abruptly switched to a no-carb diet. Such rapid weight loss is attributed to water loss. Low carbohydrate intake depletes liver and muscle glycogen (stored sugars) and water molecules linked to these sugars. This depletion triggers a drop in body weight.
Especially during the introduction phase of a low-carb diet (2 weeks), the dieter is encouraged to eliminate virtually all carbohydrates from the diet. Even a slight intake of high glycemic foods during this phase would cause immediate weight gain by rebuilding glycogen stores.
Because carbohydrate is the body's preferred fuel source, this first phase of the diet would most certainly challenge exercise enthusiasts.
So, is the low-carb lifestyle right for you? Maybe. We hope that this series of articles has helped you understand low-carb diets and their potential impact on the body.
SOURCE: (International Sports Sciences Association; Frederick C. Hatfield, Ph.D.; 2001)
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