contribute  30  percent  of  the  calories.  Saturated fat intake should be no more than 10 percent of the total calories. Cholesterol may be limited to 300  milligrams  (mg)  per  day. Many  fats  act  as  carriers  for  the  fat-soluble vitamins  A,  D,  E,  and  K;  they  also  act  both  as a  padding  for  vital  organs,  particularly  the kidneys, and as subcutaneous tissue to help con- serve body heat. Fat is stored as adipose (fatty) tissue to form a reserve supply in time of need. Fats delay gastric emptying and promote satiety. Excess calories from fat may produce obesity, the forerunner   of   arteriosclerosis,   hypertension, gallbladder  disease,  and  diabetes.  Too  little  fat in  the  diet  may  lead  to  being  underweight,  having insufficient  padding  for  the  vital  organs,  and lowered   energy.    Dietary  sources  of  fats  are butter,  margarine,  cream  cheese,  fatty  meats, whole milk, olives, avocados, egg yolks, nuts, and vegetable oils. CARBOHYDRATES Carbohydrates  (sugar  and  starches)  are  the most  efficient  sources  of  energy  and  are  known as the “fuel of life.” They are abundant in food. The  Senate  Select  Committee  on  Nutrition  and Human Needs, 1977 Dietary Goals for the United States,   Second   Edition,   recommends  that complex  carbohydrates  and  naturally  occurring sugars make up 48 percent of total caloric intake, and  refined  and  processed  sugars  10  percent. Each  g  of  carbohydrate  yields  4  calories  in  the process  of  its  metabolism.  Carbohydrates  must be reduced to glucose before they can be used by the  body.  Carbohydrates  are  stored  in  the  liver as  glycogen.  The  glycogen  is  broken  down  and released as glucose at the exact rate needed by the body.  This  mechanism  is  controlled  largely  by insulin from the pancreas. During fasting glycogen is rapidly depleted, which leads the body to use its  fat  for  energy. The  main  functions  of  carbohydrates  are  to (1)  furnish  the  main  source  of  energy  for muscular work and nutritive processes, (2) help maintain  body  temperature,  (3)  form  reserve  fuel, (4)  assist  in  oxidation  of  fats,  and  (5)  spare protein   for   growth   and   repair.   Excess   carbo- hydrates are converted into adipose tissue. Dietary sources  of  carbohydrates  are  fruits,  honey,  sweets, legumes,  potatoes,  grains,  sugars,  and  grain products. MINERALS Although   the   mineral   elements   constitute only  a  small  portion  of  the  total  body  weight,  they enter  into  the  activities  of  the  body  to  a  much greater degree than their mere weight would in- dicate. Table 3-1 lists the essential elements, the foods  that  contain  them,  and  their  functions. Certain  mineral  elements  are  essential  for  specific body functions. It is not known exactly how many of the mineral elements are indispensable to the body functions, but changes of concentration that may  seem  small  can  be  fatal.  These  essential inorganic elements contribute overwhelmingly to the skeletal framework of the body and the teeth and are an essential part of many organic com- pounds.  They  form  an  integral  part  of  all  cell structure  and  circulate  in  body  fluids.  In  addition, they exercise specific physiological influences on the function of body tissues. For the mineral needs to be met satisfactorily, the consumption of each element  must  be  sufficient  to  cover  body  tissue requirements and to meet changing physiological needs. It was once believed that any diet that was adequate in other respects would also provide an adequate intake of the essential minerals. This is not true. Foods vary greatly in their mineral con- tent. Depending on growing conditions and stor- ing  and  preparation  procedures,  they  may  vary considerably  in  nutritional  content. VITAMINS Vitamins are essential substances present in food in minute quantities. Although they do not furnish energy or act as tissue building materials, they  do  act  as  catalysts  in  many  body  chemical reactions and are necessary for normal metabolic functions,  growth,  and  health  of  the  human  body. Their  absence  results  in  malnutrition  and  specific deficiency  diseases.  Their  chemistry  is  complex and  nutritional  experimentation  is  difficult,  so our  knowledge  of  them  is  being  continually supplemented and revised. It is quite possible that additional vitamins will be discovered or that some of those already recognized may prove to contain more  than  one  factor. Vitamins are so widely distributed in food that a properly prepared normal diet usually provides an   adequate   amount.   Some  are  destroyed  in preparing  or  preserving  certain  foods.  Some manufacturers add vitamins to their products to replace  those  destroyed  or  removed  in  processing. Fat-soluble vitamins A, D, E, and K can be stored in  the  body.  It  is  possible  to  consume  excessive 3-2