Page 171 - Nutrition Essentials for Nursing Practice

CHAPTER 7 Energy Balance 159

Table 7.2 Factors That Affect BMR

Variables Effect on Metabolism

Age Loss of lean body mass with age lowers BMR.
Growth The formation of new tissue, as seen in children and

Stresses during pregnancy, increases BMR.
Stresses, such as infection and many diseases, raise
Thyroid hormones:
tetraiodothyronine BMR.
(thyroxine, or T4) and An oversecretion of thyroid hormones (hyperthyroid-
triiodothyronine (T3)
ism) speeds up BMR; undersecretion of thyroid hor-
Fever mones (hypothyroidism) lowers BMR. The change
may be as great as 50%.
Height BMR increases 7% for each degree Fahrenheit above
98.6.
Extreme environmental When considering two people of the same gender
temperatures who weigh the same, the taller one has a higher
BMR than the shorter one because of a larger sur-
Starvation, fasting, and face area.
malnutrition Very hot and very cold environmental temperatures in-
crease the BMR because the body expends more en-
Weight loss from calorie ergy to regulate its own temperature.
deficits Part of the decline in BMR that occurs with these con-
ditions is attributed to the loss of lean body tissue.
Smoking Hormonal changes may contribute to the decrease in
Caffeine metabolic rate.
Certain drugs, such as With smaller body mass, less energy is required to
fuel metabolism.
barbiturates, narcot- Nicotine increases BMR.
ics, and muscle Increases BMR
relaxants Decrease BMR
Sleep, paralysis
Decrease BMR

Physical Activity

Physical activity (PA), or voluntary muscular activity, accounts for approximately 30% of
total calories used, although it may be as low as 20% in sedentary people and as high as 50%
in people who are very active. The actual amount of energy expended on PA depends on
the intensity and duration of the activity and the weight of the person performing the activ-
ity. The more intense and longer the activity, the greater is the amount of calories burned.
Heavier people, who have more weight to move, use more energy than lighter people to
perform the same activity.

Although it is possible to get a reasonable estimate of total calories expended in a
day by keeping a thorough record of all activity for a 24-hour period, it is a tedious pro-
cess. An easier rule-of-thumb method for estimating daily calories expended on PA is to
calculate the percentage increase above BMR on the basis of estimated intensity of usual
daily activities.