Diet Composition and Fat Balance
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People who have a difficult time maintaining a desirable body weight are experiencing the First Law of Thermodynamics with a vengeance. Once it is lodged in adipose tissue, body fat persists. To remove triacylglycerol from the fat cell, fatty acids must be mobilized by hormonally activated lipolysis and oxidized in mitochondria in muscles and other tissues. This trait perfectly suits our only truly long-term energy reserve. And adipose tissue is a marvelous invention; it stores about 4,000 kilocalories (17 MJ) per pound of pure fat, or 8,800 kilocalories (37 MJ) per kilogram of pure triacylglycerol. It insulates us against loss of heat, cushions our internal organs, and provides metabolic water when it is oxidized, so that it is equally useful in the chill of winter or the parched heat of late summer. Yet this marvelous substance has been discredited by fashion designers who have a sense of style but none of evolution and its mysteries. Alas, our labor-saving devices have now conserved so much of our energy, and our restaurants make so much available so readily, that many millions of people have become obese; non-insulin-dependent diabetes, once rare, has become commonplace, and death comes to the unmindful by what is called the Metabolic Cardiovascular Syndrome, with blood clots blocking one or more coronary arteries.
KeywordsEnergy Intake Diet Composition Respiratory Quotient Rest Energy Expenditure Lean Tissue
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