Age.—As the individual grows older, the rate of metabolism decreases until, in old age, it is not more than a third to a fifth of what it was in earlier life. This is due to a general “slowing down” of the machinery, the heart does not beat so rapidly, nor is the respiration so quick. The digestive organs, the heart, the liver, and the kidneys, cannot handle the volume of food which was required during the period of greatest physical activity. Hence, any great excess over and above that which is needed for the maintenance of the body in health will be a source of danger to the elderly person. Von Noorden claims the food requirements of individuals from
60 to 70 years of age to be reduced 10%; for people from
70 to 80 years of age to be reduced 20%; for people from
80 to 90 years of age to be reduced 30%.
Sex.—Science has proved, that there is little difference in the food requirements of men and women, provided they are alike in age, weight and size, and are doing the same amount and type of work. But women, as a rule, weigh less than men, hence their food requirements are approximately less.
Murlin finds the food requirements of pregnant women to be some what higher than of non-pregnant ones, and the requirements of the nursing mother to be higher than either (see chapter on [Pregnancy and Lactation]).
For the Child.—The factors influencing the food requirements are different, to a certain extent, from those of the adult. The main difference lies in the fact that the adult needs food only for the maintenance and repair of the body, while the child must have food, not only to cover its maintenance requirements, but to support the growth and development which should be continuous from birth to maturity. Resistance, too, must be developed during this period in order to safeguard the child through life.
The rate of metabolism in the infant is greater than at any other period of life, consequently, even if a child were one-third the weight of its parent, it would inevitably cease to grow and would become malnourished, if its food requirements were reckoned at only one-third that of the parent.
Adjusting the Food Requirements.—Taking these factors as guides for estimating the food requirements of man, it is evident that no hard and fast law can be laid down to cover all, that each individual must adjust the food intake according to the weight and activity of the body. Sherman has arranged the following table showing the energy expenditures per hour for the average man (154 pounds), per pound of body weight (these are approximate averages only).
TABLE[21]
| Sleeping quietly | 60-70 calories per hour |
| Awake, lying still | 70-85 calories per hour |
| Sitting at rest | 100 calories per hour |
| Standing at rest | 115 calories per hour |
| Tailoring | 135 calories per hour |
| Typewriting rapidly | 140 calories per hour |
| “Light exercise” (stationary bicycle) | 170 calories per hour |
| Shoemaking | 180 calories per hour |
| Walking slowly (about 2¼ miles an hour) | 200 calories per hour |
| Carpentry or metal work | 240 calories per hour |
| “Active exercise” (stationary bicycle) | 290 calories per hour |
| Walking briskly (about 3¾ miles an hour) | 300 calories per hour |
| Stone working | 400 calories per hour |
| Severe exercise, such as sawing wood | 450 calories per hour |
| Running (about 5½ miles an hour) | 500 calories per hour |
| Very severe exercise (stationary bicycle) | 600 calories per hour |