THE NORMAL DIET OF MAN 699 







determined by finding the minimum quantity on which nitrogenous equi- 

 librium can be maintained, while the Calorie needs of the body are sufficiently 

 satisfied at the expense of carbohydrate and fat. Under these conditions it 

 has been found that 35 to 40 grm. of protein may suffice. In these experi- 

 ments the protein was largely milk protein. Where animal protein is entirely 

 absent from the food a larger amount of vegetable proteins will be necessary, 

 since they are of lower ' biological value/ and .it is safe to lay down as a 

 rule that for an average man the protein ration should not be diminished 

 below 70 grm. per day. This should include different kinds of protein 

 and if possible a certain proportion of animal protein, so as to ensure that 

 all the essential amino -acids are supplied in the food. 



Some authorities have recommended the diminution of protein to the minimum 

 amount on the idea that the kidneys and other organs may suffer from the strain of 

 eliminating excess of nitrogenous waste products. But the energy metabolism of 

 protein results almost entirely in the formation of urea, an innocuous substance, which 

 can have little harmful effect on the kidneys, even if we make the unjustifiable 

 assumption that these organs, unlike other organs of the body, suffer as a result of their 

 normal functional activity. There is no doubt that many of the disorders of middle 

 life may be put down to over-feeding and lack of muscular exercise, but there is just 

 as much reason to ascribe these evils to the carbohydrates as to the proteins of the 

 diet. Indeed, it has been found that for men leading a sedentary life a moderate 

 protein and fat diet is more suitable than one consisting chiefly of carbohydrates. In 

 this case the normal stimulation to oxidation of the foodstuffs viz. muscular exercise is 

 absent, and the stimulating effect of proteins on metabolism, their specific dynamic 

 action, useless when muscular work has to be performed, is under these conditions 

 of real value to the organism. 



Carbohydrates are, as a rule, the most abundant and cheapest con- 

 stituents of any diet, and form the greater part of cereals and tubers and of 

 the pulses. Only in the arctic regions may there be a lack of this con- 

 stituent of the diet. A certain amount of carbohydrate is essential for man. 

 We shall see later that sugar is always present in the circulating blood and 

 is necessary for the normal functioning of the tissues, especially of the 

 muscles. In the absence of carbohydrate in the food this sugar is manu- 

 factured by the body out of protein. Moreover under the same circum- 

 stances there is a deficient oxidation of the fats, so that the half-oxidised 

 products of fat metabolism accumulate in the body, giving rise to acid 

 intoxication. However in temperate climates a shortage of carbohydrates 

 can arise only under artificial conditions, and no need exists for laying down 

 a minimum below which this constituent of the diet should not be reduced. 



Fats can be produced by the animal body from carbohydrate. It would 

 thus seem that, given sufficient carbohydrates in the food, there should be 

 no absolute need for fats in the diet. It is stated by Hindhede that a man 

 can be kept alive and can work normally on a diet in which fat is practically 

 absent. In such cases it is essential that plenty of green food be provided 

 in order to supply the fat-soluble accessory substance normally contained 

 in the fats of milk and of meat. This statement may be true, but it is 

 certain that it cannot be applied to all human beings. In practice we have 

 to provide for each race a minimum desirable quantity of fat, which will 



