Calories and Body Weight

KATHERINE H. FISHER AND RAYMOND W. SWIFT.

PEOPLE need a continual supply of food to supply energy for good health and well-being. The energy of food, in the form of stored chemical energy, is released as heat when the food is oxidized by the body. How much food a person needs depends on his activity and the weight he should maintain.

National and international groups of specialists in nutrition have suggested energy needs for people of all ages. The recommended energy allowances of the Food and Nutrition Board of the National Academy of Sciences-National Research Council (NRC) are the standards used in the planning of food supplies and in the evaluation of diets of Americans. The Committee on Calorie Requirement of the Food and Agriculture Organization of the United Nations (FAO) has prepared recommendations for use elsewhere.

In both systems of caloric assessment, the suggested energy values do not represent actual requirements but rather caloric levels that take into account the variations that occur within a population group.

The addition of carbohydrate to a diet provides a source of energy that the body may later oxidize to produce heat (Calories), or it may be stored as fat, or its energy may be represented by muscular exercise.

The recommended energy allowances for normal, healthy Americans have been grouped into two general categories: The Calorie allowances for adults and the Calorie allowances for children and adolescents.

The allowances for adults were patterned after the needs of a man who weighs 154 pounds and is 69 inches tall and a woman who weighs 128 pounds and is 64 inches tall, who are 25 years old, live in a temperate climate, and are fairly active physically. Adjustments for age and pregnancy and lactation were made so as to include adults who differ from such a "reference" man and woman.

The Calorie allowances suggested for children and adolescents were based mostly on standard patterns of growth rates early in life.

Although the recommended allowances are to be used solely as a guide in assessment of Calories, the values suggested for children and adolescents are less applicable to individuals than are those proposed for adults. The reasons therefor stem from the differences in physical activity, appetite, and size and composition of the body among children of all ages.

CALORIE ALLOWANCES for adults have been proposed by the NRC in terms of levels at ages 25, 45, and 65 years.

During early adulthood, when physical performance may be high, daily intakes of 3,200 and 2,300 Calories have been proposed for the 25-year-old man and woman, respectively.

As adults approach middle age and physical activity lessens, 3,000 and 2,200 Calories each day, respectively, have been suggested as enough to meet the energy demands of most 45-year-old men and women.

A further reduction in caloric intake has been recommended at age 65 in order to account for still lower physical expenditures and for the gradually decreasing basal metabolism. (Basal metabolism is the energy expenditure of the body during physical, digestive, and emotional rest.)

The daily Calorie values suggested for older people are 2,550 Calories for men and 1,800 Calories for women.

Extra Calories are needed to compensate for the increased energy demands of women during pregnancy and lactation. Because the energy costs and the reduced activity in the early stages of pregnancy balance one another, the addition of 300 Calories each day has been recommended only for the second half of the reproduction period.

The extra needs for Calories during lactation, however, are greater and more constant. It has been suggested that a daily supplement of 1,000 Calories should more than satisfy the energy needed for the average rate of human milk production (about 29 ounces a day). Nevertheless, about 130 Calories of food energy should be allotted for each 3.5 ounces of milk produced.

Size, activity, and rate of growth are the standards used in assessing the caloric needs of infants 12 months old or less. Based on body weight, a recommendation of about 55 Calories per pound (age 2 to 6 months) and about 45 Calories per pound (age 7 through 12 months) has been made to meet the energy demands during this period of fast growth. No recommendation was made for the first month of life, when many babies are breast fed.

The same caloric value has been recommended for both boys and girls in the preschool and early school years. The 1- to 3-year-old child has a daily need of about 1,300 Calories, and 1,700 Calories should provide enough energy for the 4- to 6-year-old boy or girl. For boys and girls 7 to 9 years old, 2,100 Calories are recommended; for those 10 to 12 years old, 2,500 Calories.

The adolescent years, 13 through 19, have an additional need for all nutrients, including food for energy. Because the curves of maximum growth are different for boys and girls at this period, separate energy values have been proposed.

The adolescent girl has her greatest daily energy need between the ages of 13 and 15 years--2,600 Calories. In the post adolescent period (16 through 19 years), 2,400 Calories are recommend.

The period of greatest energy need of adolescent boys occurs during the years 16 through 19. A daily intake of 3,600 Calories is recommended for them. Before this period of maximum energy intake, 3,100 Calories a day (age 13 to 15) are suggested.

The number of Calories should be adjusted when the conditions of environmental temperature, size of body, or activity differ from the factors used in determining the standard energy allowances of adult men and women.

The average temperature within the continental United States corresponds rather closely to 68 F. (20 C.) used in the standard energy allowances. Although metabolism is affected by environmental temperature, most people avoid actual exposure to excessive heat or cold by means of clothing and control of indoor temperatures.

When a person's body size differs from the values stated for the "reference" man and woman (154 pounds and 128 pounds, respectively), an adjustment in the energy intake must be made.

The first step in calculating the approximate Calorie need of an individual is to determine his desirable weight for his height (table 1, above).

For example, the desirable weight of a man 5 feet 6 inches tall (66 inches) is 142 14 pounds. This means that the desirable weight may be from 128 to 156 pounds.

The second step in calculating the approximate Calorie need of an individual is a consideration of age for this desirable weight (table 2). For example, a 43-year-old woman, weighing 110 pounds, needs about 1,950 Calories a day.

The one factor that may cause considerable variation in the actual energy requirement of adults, children, and adolescents is the amount of physical activity they perform. An adjustment must be made when a person's degree of physical performance differs from the rate of activity described in the standard energy allowance.