Holistic weight reduction - Part6 - The Biochemistry of Metabolism -Carbohydrates

SOME KNOWLEDGE about the biochemistry of the metabolism of the three major energy sources is also appropriate for anyone undertaking weight reduction. This is because of the interrelationships between these energy sources and the way they are handled by the body after they have been ingested as part of a meal. The word metabolism includes the process of absorption of the energy containing substances from the gastrointestinal tract, their passage through the blood stream to different storage sites, the later mobilization during periods of increased demand, their breakdown in the cells of the body and disposal of waste products out of the body.

CARBOHYDRATE METABOLISM

Common staple foods contain significant amounts of carbohydrate in the form of starch. Rice, bread made from wheat, food products made from corn, and the wide variety of foods prepared from potatoes and yams contain large percentage of carbohydrate in the form of starches, which are polymers of simple sugars. A large number of fast foods are also made of starch, as are many snacks and coated with simple sugars, mainly sucrose which contain equal amounts of glucose and fructose. Foods containing sugar and starch empty fairly rapidly from the stomach into the intestine. Because simple sugars are rapidly absorbed from the upper part of the intestines into the blood stream, they are able to meet energy demands swiftly. Insulin producing cells of the pancreas constantly monitor blood sugar levels and secrete appropriate amounts of insulin into the blood stream to maintain blood sugar levels in the range of between 70-120 mg. Insulin is the most important metabolic hormone in the body and drives the glucose present in blood into all the tissues of the body depending on their energy needs. Glucose that is not immediately utilized by the body is taken up by the fat cells of the adipose tissue and is converted into a substance called alpha glycerophosphate and is combined with fatty acid molecules to create neutral fats called triglycerides. In the other tissues of the body, glucose is broken down into smaller molecules and oxidized to produce energy. In muscle tissue and liver, a significant portion of glucose is also converted into its storage form called glycogen. If blood glucose levels rise above 180 mg%, the kidney excretes the excess amount of glucose into urine and thus its energy content is lost to the body, as happens in diabetes. The role of insulin is primarily to maintain blood sugar level within a small range and secondarily to increase storage of all excess energy intake as fat molecules thereby preventing the loss of scarce energy resources, a capability that was very important in primitive times. Since the amount of insulin secreted from the pancreas is directly proportional to the rate of rise in blood glucose, any food that is rich in sugar content if consumed in excess of immediate energy needs, results in large amounts of insulin secretion which in turn causes the formation of neutral fat in adipose tissue. Refined sugars especially tend to predispose to accumulation of fat. Complex sugars such as starches are absorbed much more slowly from the gastrointestinal tract, because they have to be broken down into simple sugars before they can be absorbed through the lining of the intestines into the blood stream. This causes a less rapid rise of blood sugar level and consequently less secretion of insulin and significantly less conversion of absorbed sugar into fat depots. When sugars are broken down into smaller molecules, carbon dioxide and water are formed. If there is excess availability of these smaller fragments called ‘two carbon fragments’, they are synthesized by the liver into fatty acids, and into cholesterol. Part of it is converted into triglycerides and sent to the fat depots of the body, from where they can be mobilized when more energy than is available from glucose, fatty acid molecules and aminoacids already present in the blood stream is required for the needs of the body. Such mobilization usually occurs 3-4 hours after a meal when blood sugar levels begin to reach the lower levels of the normal range and becomes maximal during major physical activity or overnight when food intake has been absent for close to 8-10 hours after the last meal. Thus there is a reciprocal relationship between the levels of glucose and fatty acids in the blood stream controlled by the blood glucose levels and plasma insulin levels. Early in the morning when blood glucose level is low, insulin level is also low and fatty acid level is high. After food intake blood glucose level and plasma insulin levels rise to what are called post-prandial levels and later fall to a lower stable level by about 3-4 hours after the meal. During this 3-4 hour period after each meal, glucose may provide most of the energy requirements of the body if large amounts of carbohydrate is consumed, whereas during the rest of the day and night, energy demands of the body are met mainly by the catabolism of fatty acids. As emphasized before, the brain uses glucose as its main source for energy production during all 24 hours of the day. During periods of exercise, fatty acids provide most of the energy requirements of the working muscles including that of the heart.

About the Author : Abe Kurien MD, is a proponent of holistic medicine. He writes profusely on subjects of Weight reduction. His enlightening articles can be found on the smatix weight reduction section : Health and Nutrition Guide

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