ESTIMATION OF ENERGY EXPENDITURE
Basal metabolism is the process in which energy is produced by the body. The amount of
energy used by the body at rest is called the basal metabolic rate, or the BMR. About 60
to 70 percent of the energy
used by your body during the day is to maintain the body's systems, such as digestion of
food, beating of the heart, breathing, maintaining body temperature, and many other
life-sustaining functions. If you consume more calories than needed for basal metabolism,
you will need to burn these calories off with some form of physical activity.
Several factors determine the basal metabolic rate. Age is the one of most influencing
factors; generally, the younger you are, the higher your BMR. This is due to the fact that
during infancy and childhood there are many growth spurts requiring high amounts of
calories. After you reach 30, your BMR slows down by a rate of one to two percent a year.
It becomes increasingly harder to lose and keep weight off as you grow older. The
"middle-age spread" is often a result of a slowing of the BMR and an inclination
to be inactive.
Another significant factor is the influence of your body composition. Muscle tissue is
highly active even at rest. The more muscle tissue in your body, the higher your BMR. Men
usually have a higher BMR because of their greater tendency toward lean muscle tissue.
Hormones also play an important part in basal metabolism. The BMR is likely to change
during puberty and pregnancy due to hormonal changes.
FOR MORE ENERGY, STAY IN ZINC
According to a recent USDA study, eating foods high in zinc may help prevent fatigue
and increase endurance. Researchers placed 12 men on a diet containing 18 milligrams (mg)
of zinc for 9 weeks, then fed them only 3 mg for 9 more weeks. Exercise tests showed that
they fatigued faster and their blood levels of carbonic anhydrase--an enzyme that protects
against sore muscles --were 10 to 12 percent lower when they ate the low-zinc diet,
explains Hank Lukaski, Ph.D., the research leader. To keep zinc up and fat down, eat lean
cuts of red meat.