IV. Energy Storage Problems Henry A. Bent North Carolina State University Raleigh. 27650
Much of sugar's behavior (see Part 111) illustrates the well-known rule that like dissolves in like. Thus sugar (GCHOH-) dissolves in water (HOW. And water is absorbed by sugars and other carbohydrates: table sugar cakes in humid weather, wood (cellulose) swells in moist climates, and muscle-stored carbohydrate carries hydrogen-bonded to it into muscle cells nearlv three times its mass of water. Watered stock i i not a new deceit. Manufacturers water fat on the shelf ("Diet Margarine" is fifty-seven percent water, corresponding closely in composition, if not in structure, to a "hvdrocarbohvdrate": HnC.H?O) - .. as formerlv farmers wat e r ~ dpnrteillon-the hoof, and a always ~ H t l l rhas i watered carhohsdratcr in muscles. For quick energy it might seem best to store in working cells elucose and other simple sugars. Unfortunately for that &heme the cells would tend to swell-up and burst, through osmosis, unless their syrup solutions were relatively dilute, or unless metabolic energy was continuously expended to pump water out of the cells. T o thwart osmosis, animal cells polymerize simple sugars into the insoluble polymer glycogen, plant cells into a similar, less branched, longer chain polymer starch. To lay away in that way a forty-day supply of fuel for lean times would require, however, carrying around about 160 pounds of excess ~
~
--
havurarre ..-= -
keal
2400 -X 40 day X day
1g dry glycogen 4 kcal
.w.
3gwater
1 lb x -= I G 11,~
' 454 g -" 'T o avoid becoming excessively deliquescent, the body sequesters most of its standby fuel in subcutaneous deposits of hydrophobic fat, or "blubber," which is easily oxidized, has a large enthalpy of combustion, is non-explosive, has a good shelf-life, and is light. A forty-day supply of fat weighs about 25-30 pounds.
I g dry
Caloric Deficits and Weight Loss In brief, crash diets' caloric deficits are met largely by oxidation of muscle glycogen. Loss of water hydrogen-bonded to the glycogen consumed yields large initial weight losses. One 2400-kcal dav on an input of, for example. 1000 kcal of celery and cottage cheese, dr; toast, and tea, iields an energy deficit of 2400 - 1000 = 1400 kcal, corresponding to the oxidation of 350 grams of muscle glycogen (350 X 4 = 1400). Released simultaneously and soon lost by the body are 3 X 350 grams of bound water. Total mass lost is 4 X 350 = 1400 grams or 3 pounds of hydrated glycogen, and essentially zero pounds of fat. Fat is !
