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Fate of the Carbohydrates when They Are Ingested in Excess 1

sugar, alimentary, blood, glycogen, urine and fat

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1. Glycogen Storage.—The second contingency which we have now to consider is encountered when there is an excessive supply of car bohydrates. When the excess is but moderate and of short duration, there occurs, as we have shown above, a filling of the glycogen re servoirs in the liver and muscles. But the capacity of these reser voirs is limited. It is estimated that about 300 grams of glycogen may be stored up iu the human organism. Consequently, if the car bohydrates continue to be ingested in large quantity, and if, at the same time, by reason of a sedentary habit, but a small amount of carbohydrates is consumed in the muscles, the capacity of the stor age depots in the body is soon overtaxed. What now happens de pends upon circumstances, whether, namely, there is a sudden _flood ing of the body with carbohydrates, as, for example, when there is single excessive ingestion of sugar, or whether there is a more mod erate over-ingestion of carbohydrates continued for a series of clays or weeks.

2. Conversion of Carbohydrates into Fat.—The last-mentioned case is by far the most frequent. The problem thus presented to the organism is how to dispose of the superfluous material. It solves this problem by converting the excess of carbohydrates, for which there is no more room in the glycogen depots, into fat, and then stor ing this in the capacious fat reservoirs in the subcutaneous connective tissue and other parts of the body.

3. Alimentary process of conversion of carbo hydrates into fat requires a certain time, and so it may happen that by repeated accessions so much carbohydrate is taken up into the circulation from the intestinal canal that neither the consumption in the muscles, the storage in the liver and muscles, nor the conversion into fat is sufficient to dispose of the on-pressing stream.

The blood thus naturally becomes abnormally charged with carbo hydrates, a condition of hyperglymmia resulting. We have already seen that when the percentage of sugar in the blood is normal, neither the kidneys uor any other of the glands excrete more than mere traces of sugar. The condition is otherwise in the case of hypergly

mmia; as soon as the percentage of sugar in the arterial blood ex ceeds 0.2, the renal filter becomes inadequate and glycosuria results. When I mention about 0.2 per cent. as the limit beyond which gly cosuria arises, I do so with a certain reservation. The limit for man is, indeed, not exactly defined and may be subject to certain fluctua tions. The fact that the quantitative estimation of sugar in the blood is exceedingly difficult interferes with the more exact determination of this limit. Most of the estimates that we have date from an ear lier period when this difficulty was not sufficiently appreciated. The variety of glycosuria which is produced in the manner just described is called alimentary ylycosevia. It is a purely physiological process and has nothing whatever to do with the disease called diabetes mellitus. It is very important that the physician should have an exact under standing of the mode of origin and significance of alimentary glyco suria, for the diabetic and alimentary forms of glycosuria are often confounded. We may, therefore, briefly set forth here the most im portant practical points relating to the physiological and alimentary excretion of sugar : (a) Traces of sugar (1 to 2 decigrams to the litre) are, indeed, present in the urine under ordinary conditions of nutrition, but as none of the usual sugar tests gives any indication of this small percen tage, healthy urine must be regarded practically as sugar free.

(b) Sugar is present in the urine after the ingestion of various saccharine substances, provided they have been taken in considerable amount within a brief period.

(c) The sugar appearing in the urine under these circumstances is always of the same kind as that ingested in excess ; if it be glucose, for example, we have glycosuria, lactose—lactosuria, levulose—levu losuria, saccharose—saccharosuria.

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