Protein Forms tissue \ White of eggs (albumen), (muscles, tendon, } curd of milk (casein), lean and probably } All serve as meat, gluten of wheat, etc. fat) } _fuel_ and yield } _energy_ in form Fats Form fatty tissue. } of heat and muscular Fat of meat, butter, olive oil, } strength. oils of corn and wheat, etc. } } Carbohydrates Transformed into } Sugar, starch, etc. fat. / Mineral matters (ash) Aid in forming bone, Phosphates of lime, potash, assist in digestion, soda, etc. aid in absorption and in other ways help the body parts do their work. Water used as a vehicle to carry nutrients, and enters into the composition of living matter. Footnote 36: Adapted from Atwater, _Principles of Nutrition and Nutritive Value of Food_, U. S. Department of Agriculture, 1902. Common Foods contain the Nutrients.--We have already found in our plant study that various plant foods are rich in different nutrients, carbohydrates forming the chief nutrient in the foods we call cereals, breads, cake, fleshy fruits, sugars, jellies, and the like. Fats and oils are most largely found in nuts and some grains. Animal foods are our chief supply of protein. White of egg and lean meat are almost pure protein and water. Proteins are most abundant, as we should expect, in those plants which are richly supplied with nitrogen; peas and beans, and in grains and nuts. Fats, which are melted into oils at the temperature of the body, are represented by the fat in meats, bacon, pork, lard, butter, and vegetable oils. Water.--Water is, as we have seen, a valuable part of food. It makes up a very high percentage of fresh fruits and vegetables; it is also present in milk and eggs, less abundant in meats and fish, and is lowest in dried foods and nuts. The amount of water in a given food is often a decided factor in the cost of the given food, as can easily be seen by reference to the chart on page 283. Refuse.--Some foods bought in the market may contain a certain unusable portion. This we call refuse. Examples of refuse are bones in meat, shells of eggs or of shellfish, the covering of plant cells which form the skins of potatoes or other vegetables. The amount of refuse present also plays an important part in the values of foods for the table. The table[37] on page 276 gives the percentages of organic nutrients, water, and refuse present in some common foods.