HUMAN STRUCTURE AND LIFE-ACTIVITIES 501 



expensive than fat meat or butter when we consider that 

 fat has 9 calories per gram, and hence has more than double 

 the energy value of protein, which has 4 calories per gram. 



424. Mixed Diet. The three reasons given above have 

 led all physiologists to advocate a mixed daily diet containing 

 (1) the protein necessary for daily repair, and for growth in 

 early life ; and (2) enough non-nitrogenous foods to furnish 

 the necessary heat and muscular energy. Whether these 

 foods for energy should be fat or carbohydrates depends upon 

 availability and digestibility. One man may digest and 

 use 100 grams of fat and 300 of starch as well as another could 

 use 50 grams of fat and 412 of starch ; but the energy obtained 

 is nearly the same. 



Special foods are not known for special organs. That 

 celery is a " nerve " food, fish a " brain " food, lean meat a 

 " muscle " food, etc., are popular beliefs which are entirely 

 without scientific foundation. 



It is not yet known whether proteins from plants are 

 equally valuable with those from meat. Certainly many 

 people have lived well on a vegetarian diet ; but those who 

 adopt it in its strictest form without milk, cheese, and eggs 

 should eat more than 60 grams of protein, because it is 

 probable that the human cells select only certain kinds of 

 plant proteins for use in repair and growth of protoplasm. 



It also should be noted that with a strict vegetarian diet 

 there may be difficulty in getting enough protein without 

 an excess of carbohydrates, because there is relatively little 

 protein in many plant tissues. However, certain seeds (es- 

 pecially beans, peas, 'lentils, wheat, rye, and oats) contain 

 much more protein than the foods obtained from" green vege- 

 tables " (roots, stems, and leaves of plants). Hence, it is 

 possible by using such seeds to make a strict vegetarian diet 

 with proper proportions of protein and other food. How- 

 ever, the safest way for most people is to add milk and its 

 products and eggs to plant foods, if one has tastes or principles 



