EXERCISE AND WEIGHT
CONTROL
by Dr. Ed McLaughlin
As a health professional, I can guarantee that on a daily basis a patient will
express the desire to lose weight. I am certain that they mean they would like
to lose fat, and become leaner, to be more accurate. The presence of overweight
or obesity can indeed be said to be epidemic in modern society, and has known
consequences on the heart and joints, not to mention the accompaning problems
of self-esteem and embarrassment. Yet from a medical standpoint, we still have
great limitations in treating weight problems: the drugs available for weight
control have plenty of side effects and do not have a track record for long-term
success. A better understanding of obesity may emerge from the recent unravelling
of the human genome and other research, but in the meantime, what can we do to
be helpful?
Diet and Exercise
Dieting alone is often a frustrating process. Fad diets come and go on a regular
basis, and can sometimes help with short-term weight loss, but the likelihood
of regaining the weight is high. The addition of exercise can be quite valuable
due to the following principle: exercise will raise the resting metabolic rate
for several hours afterwards! The actual energy useage during exercise is much
less than people might think (and much less than they would like). For example,
I recently pedaled away on an exercise bike in a gym, and after 30 minutes, pushed
the button to get a readout on calories burned, and the number "200" lit
up. Not very much indeed, and I knew that fewer than half the calories came from
fat stores! About the number of calories in the small yogurt container I was
eyeing for a snack later on.
Energy metabolism
Humans have two main fuels available for exercise, carbohydrates (glucose and
its storeage form, glycogen), and fats. Some members of the animal kingdom are
well-adapted to burning fats. For example, wolves and migratory birds can metabolize
fat stores allowing them to travel long distances without new food sources, but
humans are not so lucky. Even during sleep or rest, we burn a mix of fats and
carbohydrates, about 60% fats and 40% carbs.
There are some interesting differences between carbs and fats that will help
us understand human metabolism. It can be said that we humans are very good at
burning carbs, and also quite good at storing fats. Our ability to store carbohydrates
is limited to about 2000 kcal (kilocalories, the unit used to measure energy
supplied by food and energy burned during exercise). Curiously, a highly trained
endurance athlete needs about 2000 kcal to run a marathon! The amount of calories
we store as fat is well over 100,000 kcal, even in a lean person, enough to run
several consecutive marathons. But storage amounts are only part of the story.
In a laboratory setting, the mix of fuels being combusted for energy production
by an exercising person can be determined by measuring the mix of oxygen and
carbon dioxide being exhaled, but that's another topic entirely. Suffice it to
say that these matters of exercise physiology have been well described in recent
years by research scientists. From these types of scientific studies, it is known
that as we begin to exercise, the percent of fuel provided by carbohydrates goes
up due to its greater fuel efficiency, meaning greater energy production per
liter of oxygen taken in. In fact at maximal effort, the fuel being used is 100%
carbohydrates. This has led to some misunderstanding that is fairly widespread,
in which the advice is given to "workout at lower intensity in order to
burn more fat". Lower intensity will burn a higher percentage of fat, but
the absolute amount of fat burned is quite small. A pound of body fat is equal
to 3500 calories of fuel, enough to exercise for several hours if we had the
metabolism of migratory birds. But that 3500 calories in humans translates to
several hours of exercise. So while the amount of fat calories burned during
exercise is not so great, the metabolic rate after exercise will rise and stay
elevated for several hours. In fact, the rise in post-exercise metabolism is
greater after intense exercise than after mild or moderate exercise! And recall
that at rest, fat is the predominant fuel being used. So for those persons in
whom weight loss, or fat loss, is a worthy goal, regular exercise will be a great
help to modification of the diet. It doesn't mean that all overweight persons
should begin training to run a marathon, but regular walking at a tolerable rate
for 20 minutes or more on most days of the week is a reachable goal for most.
Purchasing a good pair of athletic shoes intended for walking or running is a
nice reward for getting started! So lace up those shoes and get started. Your
metabolic rate will thank you!
Charles E. McLaughlin, M.D.
–copyright © 2008,
Dr. Ed McLaughlin
DISCLAIMER
Medical information on the DrEd website (sportsmed.info) is intended for educational
purposes only and is not intended to be a substitute for medical advice. Always
contact your doctor if you feel you need medical advice or treatment.
