Basal Metabolism (continued)

When we eat, our food is broken down biochemically in the mitochondria through the process of thermogenesis. This usually takes 10% of the total 100% basal metabolic rate for a day. The other 70% of the 100% total of our daily basal metabolic or resting metabolic activity occurs within the organs of the body: liver 27%, brain 19%, heart 7%, kidneys 10%, skeletal muscle 18%, other organs 19%. The final 20% of the total 100% of daily basal or resting metabolic rate comes from physical activity.

What unifies the basal metabolism in thermogenesis, in resting metabolism or through activities of daily living is the need to process all of our substrates with oxygen and then to consume the production that occurs as carbon dioxide which is explained by the Krebs cycle. So the value of our food is certainly there for our survival, but there are relative meanings to how the body uses energy to keep our organs functioning normally based on the rate of oxygen needed to break down food biochemically.

For example, because the ratio of hydrogen to oxygen atoms in all carbohydrates is always the same as that in water, that is 2 to 1, all of the oxygen consumed by the cells is used to oxidize the carbon in the carbohydrate molecule to form carbon dioxide. Consequently, during the complete oxidation of a glucose molecule, six molecules of carbon dioxide are produced and six molecules of oxygen are consumed.

The overall equation for this reaction is:

    C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

Because the gas exchange in this reaction is equal, the R.Q. for carbohydrate is unity or 1.0

    R.Q. = 6 CO2 / 6 O2

The chemical composition for fats differs from that of carbohydrates in that fats contain considerably fewer oxygen atoms in proportion to atoms of carbon and hydrogen. Fats are generally divided into 6 categories: total fats, saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, dietary cholesterol, and trans fatty acids. From a basal metabolic or resting metabolic perspective, more energy is needed to burn a saturated fatty acid than an unsaturated fatty acid. The fatty acid molecule is broken down and categorized based on the number of carbon atoms on its molecular structure.

The chemical equation for metabolism of the 12 to 16 carbon atoms on a saturated fatty acid molecule shows the difference between metabolism of carbohydrates and fatty acids. Palmitic acid is a commonly studied example of the saturated fatty acid molecule. When palmitic acid is broken down more oxygen is needed and more carbon dioxide is produced but the respiratory quotient moves below unity to account for the increased energy required to burn fat molecules (generally 9 calories per gram of fat versus 4 calories for a gram of carbohydrate or protein.)

The overall equation for the substrate utilization of palmitic acid is:

    C16H32O2 + 23 O2 → 16 CO2 + 16 H2O

Thus the R.Q. for palmitic acid is 0.696.

    R.Q. = 16 CO(2) / 23 O2 = 0.696

There are several companies that are testing the public for this value to assist with weight loss. It is theorized that if a person can more accurately know what amount of energy is needed to survive, then a person can select consumption patterns to more efficiently match what is required by the body for daily activities. Thus the emphasis shifts from caloric restriction which slows the BMR or RMR, and causes frustration of weight management goals, to substrate utilization which focuses on what the body needs to stay healthy.

By measuring the carbon dioxide expended (VCO2) in ml/min and dividing that by oxygen consumed (VO2) in ml/min you can determine the R.Q. which can then be compared to heart rate for purposes of application.

What is interesting about the study of basal metabolism or resting metabolism is the paradoxes that are inherent in its formulas for prediction. For example if muscle is the principle determinant of resting metabolism, why does metabolic rate go up when we gain weight and become weaker physically due to loss of muscle mass from caloric restriction? Why does metabolism go up when we drink coffee which has no appreciable effect on muscle gain?

Why is metabolism different for different cultures requiring different formulas to be devised by scientists with equipment that measures the rate with extreme precision? Why do we assume that 2,000 kcals are the standard amount of nutrition needed for a woman to survive daily, and 2,500 for a man when the basal metabolic rates are so different in all the studies that are performed on this topic each year?

That is why weight management is a very difficult undertaking requiring sophisticated expertise. Each person is unique and their metabolism is also unique. Menopause affects metabolism but in different ways for different people.

Weight training can have a longer impact on metabolism than aerobic training, but there are no formulas currently written which can predict the length and duration of a raised metabolism from trophic changes with anabolic neuromuscular training. Careful graphing of the bodies response to rest or exercise with a gas analyser that also records heart rate, is one attempt that scientists use to measure the variation in basal metabolic rate between subjects.

Gastric Bypass surgery also has implications because it affects the storage capacity of the body by closing the contents of the stomach and bypassing the intestines. Thermogenesis is impaired, the ability to consume fruits and vegetables are drastically reduced, and the essential nutrients are rationed so that a healthy diet becomes problematic.

Knowing what the body burns at rest or through exercise yields (via heart rate monitoring) a targeted program of energy utilization based on metabolic performance. The resting heart rate is correlated to the resting metabolic rate because of the singular contribution made by the heart to survival. By measuring heart rate we can then derive estimations of what level of substrate utilization is actually causing biochemical metabolism in our bodies at rest or in activity.

This in turn can help a person to maintain an appropriate level of consumption and utilization through heart rate monitoring confirmed by blood tests, gas analysis using either direct or indirect calorimetry, to show the effect of substrate utilization. Thus basal metabolic rate or resting metabolic rate are becoming essential measures to maintain healthy body weight for survival throughout the lifespan.

Source: Wikipedia.org