110 Metabolism of Healthy Man. 



influence of diet on body-weight and the store of water. 



Nearly all experimental diets differ widely from the normal. In some diets 

 there is a large preponderance of carbohydrates, or of fat; occasionally there 

 is a large proportion of protein. Rarely is an experimental diet so evenly ad- 

 justed as to correspond exactly to the diet on which people commonly live. 

 A striking series of experiments has demonstrated very clearly that a change 

 from a diet poor in carbohydrates to one rich in carbohydrates is accompanied 

 by a considerable retention of water by the tissues of the body. Conversely, 

 it is shown that when a change is made from the rich carbohydrate diet and a 

 fat diet is substituted, there is a considerable loss of water to the body. It is 

 obvious, therefore, that if a change is made from a normal diet to one con- 

 taining an excessive proportion of carbohydrates, even though the total nutri- 

 ents in the food may be insufficient for the maintenance of the body, the excess 

 carbohydrates may cause the retention in the body of a sufficient amount of 

 water to more than make up for the loss in body-material resulting from the 

 decrease in the total food-supply. Moreover, the body must draw upon its 

 body-material, chiefly fat, and with a diet such as is under discussion, the loss 

 of 100 grams of fat, furnishing some 900 calories of energy, may be compen- 

 sated by the addition of 100 grams of water to the body. These facts will not 

 be seen from a mere observation of change in body-weight, and one must be 

 very careful in drawing deductions from such changes, particularly in experi- 

 ments of short duration. 



Effect of Transition from Large Carbohydrate to Large Fat Diet. 



The influence of marked changes in diet upon the body-weight has been 

 shown in connection with a series of experiments conducted in the laboratory 

 of Wesleyan University. 1 The diet of the subject in this series was for three 

 days largely carbohydrate. It was then suddenly changed to a diet having 

 equal energy which, however, was derived in large part from fat. The changes 

 in body-weight during the series were most remarkable and interesting. The 

 series consisted of work experiments, and the amount of energy in the diet 

 was, therefore, large. During the carbohydrate period there were ingested 

 about 970 grams of solid matter each day and sufficient water in food and 

 drink to make the total weight of food and drink about 4500 grams per day. 

 During 3 days on this diet, the body-weight as determined by a platform balance 

 increased on the average 61 grams per day. The more accurate determinations 

 of the gains and losses of body-material calculated from the amounts of protein, 

 fat, carbohydrates, water, and ash katabolized showed an average gain of 88 

 grams per day. 



On the fourth day of the series, the diet was so changed that the greater 

 part of the energy came from the fat rather than the carbohydrates. The fat 



1 Benedict and Milner, U. S. Dept. Agr., Office Expt. Stas. Bui. 175, 1907. 



