A Perspective on the Physiology of Fasting & Weight Loss – Part Two

When a meal is digested, the calories released are used to replace liver and muscle energy stores as glycogen and operate the nervous system. Oxidizing(burning) one gram of fat releases approximately 9.5 kilocalories (Calories). Oxidizing one gram of carbohydrate releases 4.2 Calories and protein 4.3 Calories. Excess calories are stored as fat. A very rough average Calorie consumption for an adult is 70 C per hour or 1680 C per day. [1] This number will vary greatly based on age, gender, physical activity, physical condition, body weight and muscle mass. However, the following rule applies to everyone. Eating more Calories than your body uses in a day results in fat storage and weight gain. Eating less Calories than your body consumes results in weight loss. In the strictest terms of calorie count, where the calories come from is irrelevant, however the speed with which calories are released during digestion can have profound effects on your sense of fullness, energy level and sense of well being. Generally sugars convert to glucose almost immediately releasing all of their calories at once. Monoglyceride fats may be immediately available for use as an energy source in the nervous system, but in general, fats and proteins are slower to metabolize, releasing their calories over time.  Of course, the issue of consuming ’empty calories’ vs. whole foods, which included micro-nutrients, vitamins & minerals is central to natural healing.

There are four basic mechanisms for producing energy. How the body uses these mechanisms to produce energy changes over time. It also depends on energy input and demand. For the first three hours after a meal our body is using glucose, glycerol and amino acids derived from carbohydrates, fats and proteins in our meal. It is also converting glucose into glycogen for storage in the liver and muscle. This process is called ‘glycogenesis‘. As stated above, excess calories are stored as fat at this time. After the initial three hours, the body enters a ‘not fed’ state, where the mitochondria inside a cell begin to break down stored glycogen into glucose in the presence of oxygen. This is called ‘ aerobic respiration’.

Intracellular glucose is almost immediately available for physical exertion, but ATP production from glucose depends on oxygen availability in the cell, which can be used up in approximately 17 seconds during physical exertion. [1] Once available oxygen is depleted, the cells must switch to an anaerobic (no oxygen required) energy production mode outside the mitochondria. This also involves breaking down stored glycogen and is called ‘glycolysis’.

At night, we enter an ‘at rest’ state during which muscle energy demand is low and skeletal muscle cells begin to break down fatty acids in a process called ‘lipolysis’. The amount of Calories burned by our muscle tissue during the night is primarily a function of our muscle mass and our basal metabolic rate (BMR), which is controlled by the thyroid. The more muscle mass you have the more calories you burn in the ‘at rest’ state. However, at rest, we may burn as few as 50 Calories per hour and it takes a 3500 C exertion to burn off a pound of fat. That’s 70 hours of ‘at rest’ fat burning. [1] It is possible to increase one’s BMR with supplements such as cayenne pepper, green tea, ephedra, ma huang or caffeine, which are often included in weight loss formulas. It is this mechanism that many supplement manufacturers allude to when they claim their product will turn you into a ‘fat burning machine’. The additional fat loss may be real, but it is minimal, while the hype is excessive!

Physical exercise temporarily raises the BMR during the day. Consistent physical exercise several times a week will maintain a higher BMR as long as one continues to stay active. If one becomes sedentary, the BMR will drop over time. Various levels and types of physical exercise will burn different amounts of calories in a given time period. Walking at 2 mph for 30 minutes, a 150 lb. adult will burn 90 Calories. Jogging (a 10 minute mile) for the same time they would burn 345 Calories. 30 minutes in a far infrared sauna at 130+ degrees Fahrenheit is claimed to burn 600+ Calories. But, these are not necessarily fat calories. Fat must be catabolized in the presence of oxygen. As we have seen above, skeletal muscles switch to anaerobic gylcolysis after just a few seconds of exertion. Therefore, fat loss is minimal during strenuous physical exertion. However, you are likely to increase oxygen capacity, tone muscle, increase muscle mass and lose inches. That’s good. It just doesn’t result in large weight loss.

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Don Gillmore, Licensed Massage Therapist(15 yrs), B.S.- Life Sciences

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3 Responses to “A Perspective on the Physiology of Fasting & Weight Loss – Part Two”

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  3. dgillmore says:

    In my post, I mentioned ephedra & mah Huang. These are the same thing and the FDA has strong warnings to the public regarding the possible serious side effects of using any product which lists their inclusion. I am not advocating their use. I am simply noting that they do elevate BMR and that they have been and may still be used in some weight loss products. For more information, please go to: http://www.personalhealthzone.com/ephedra.html