Weight Control Infocenter
Weight and Slow Metabolism: Myth or Reality?
by Caroline J. Cederquist, M.D.
Doctors and other health professionals often hear
their patients complain of a slow metabolism, certain
that they're just not burning calories as efficiently as
other people who eat the same amount.
Clinicians tend to think it's more likely that patients
are just mistaken about how much they're actually
eating. It's hard to blame them if they're a bit
skeptical, as there's a good body of research that
shows that people both under-report their intake,
and also honestly underestimate it.
But in the past, even if physicians suspected a
patient really did have a low metabolic rate, it wasn't
easy or even worthwhile to try to determine if that
The method for accurately testing metabolism was
complicated and cumbersome, and simply too
expensive to be practical in an outpatient setting.
But now, with a new instrument recently approved
by the Food and Drug Administration, clinicians can
get an accurate reading of a patient's resting
metabolic rate, or RMR, in 10 to 15 minutes.
Your RMR is the rate at which your body uses energy
just to keep its basic functions going when you're at
rest, circulation, breathing, digestion. Most people
are surprised to learn that 65 to 75 percent of our
energy is expended this way, without counting what
it takes to walk or talk or work, let alone actually
This is part of why people who try to lose weight by
exercising more, without making dietary changes,
typically get very little result for their trouble. Since
up to three-quarters of our energy is expended
without even moving, an exercise-only approach is
dealing with a pretty small proportion of the overall
calorie use anyway.
Of course, over time, a good exercise program will
speed up the RMR as well, and then people start to
see accelerated results in weight loss, but most folks
get discouraged and give up long before that
Conversely, people with a slow metabolic rate burn
less energy overall, so they will be more inclined to
gain weight, even if they're not eating any more than
the next guy.
For instance, say Betty has a slow metabolism and
Veronica has a normal one. If they go to lunch and
have the same food, then go for a walk together,
the same meal, the same walk, Veronica burns more
Sounds like a raw deal for Betty, but that's the way
it is. And the metabolism does slow down in obese
people, and once that happens, they can continue
gaining weight even if they don't ever add more to
their daily caloric intake.
So for people who seem especially prone to gaining
weight, you can see how it would be helpful to find
out if there was an abnormally slow metabolism
involved to begin with, particularly before it gets to
the point of obesity.
But for many years, the only reliable methods for
testing metabolism were direct calorimetry,
measuring precisely the amount of heat a body
released at rest in an atmospherically controlled
chamber, or indirect calorimetry, which involved
having a patient fast overnight, then capturing their
exhaled breaths in plastic bags and measuring the
content of the gases. Because the ratio of gases is
dependent on metabolic rate, that analyses provided
an accurate measure of RMR.
But these tests could really only be conducted in
research facilities, because few regular medical
hospitals were equipped with the expensive
equipment required for them, so various mathematical
formulas were developed for estimating metabolic
rate based on weight and intake.
Some worked pretty reliably for people of healthy
weight and body composition, when they were able
to accurately report what were eating. But with
the 'portion distortion' caused by the creeping
enlargement of serving sizes, even the most
conscientious patients nowadays can underestimate
And for people who are not of healthy weight and
body composition, the formulas don't apply. For
example, it takes less energy to sustain fat mass
than fat-free mass, so when a larger percentage of
someone's overall weight is in fat, there goes the
But someone has finally come up with a hand-held
device for indirect calorimetry that is practical and
affordable enough for doctors to have in their
offices. A patient basically just has to sit still and
breathe into a tube for 15 minutes, and the device
analyzes the exhaled gases and calculates the
Remember that we said that your RMR level can
actually improve. Exercise will do it as you gain
muscle, and so will weight loss itself, sometimes to a
surprising degree. Using the new indirect
calorimeters, we have often found that a patient's
RMR is higher after a 20-pound loss of fat mass than
it was before she dropped that weight.
That's a quantifiable improvement, and for a weight-
loss patient who's been struggling, that kind of
numerical proof really helps them keep up the good
THROUGH THICK & THIN:
What can cause an abnormally low metabolism?
1. Diabetes or insulin resistance (pre-diabetic
2. Higher percentage of body fat
3. Underactive thyroid function
4. Loss of lean body mass, muscle with age or
If you think you have an unusual metabolism, it may
be worth getting it tested, now that it's possible to
have that done easily and accurately. There's no
point in laboring against unseen obstacles.
How Appetite Works
Glycemic Index, now Meet the Satiety Index
If you had to choose just one food for snacking, based on how long
it would keep you from getting hungry again, what would you choose to
What if it wasnít about low-carb or low-fat, but it was about YOU?
It seems now that scientists have shown that the big variable in
deciding which is better isnít so much the fat or the carbsóitís you!
Dining Out, Weighing In:
Restaurant Meals are Higher in Calories
When we eat out, we simply have much less control over what ends up on
our plates, and from there, on our bottom line. That shows up in a
variety of ways.
Connection: Complexity in Weight Loss
You canít eat your way into healthy thinking, but you can probably
think your way into healthy eating, which in turn, actually could make
your thinking healthierÖ if only you could figure out where to start.
Caroline J. Cederquist, M.D. is a board certified
Family Physician and a board certified Bariatric
Physicians (the medical specialty of weight
management). She specializes in lifetime weight
management at the Cederquist Medical Wellness
Center, her Naples, FL private practice, you can also
get more information about Dr Cederquist and her
weight management plan by visiting