From: caf@omen.UUCP (Chuck Forsberg WA7KGX)
Subject: Re: Adiposity 101
Organization: Omen Technology INC, Portland Rain Forest
Date: Tue, 12 Jan 1993 15:23:13 GMT

In article <18004@pitt.UUCP> geb@cs.pitt.edu (Gordon Banks) writes:
>In article <1993Jan5.181328.9701@speedy.aero.org> nadel@attatash.aero.org (Miriam Nadel) writes:
>
>>>That is compatible with (1) the possibility that the caloric goal
>>>was set too high for some of the subjects, and (2) systematic
>>>errors in measuring caloric intake, as you describe later.
>>>In other words, it is not, as described, in conflict with the NEJM
>>>study.
>>>
>>It was in conflict with the report that I heard of the NEJM study which 
>>implied that *all* of the subjects were grossly underreporting their intakes.
>>
>All of the ones who failed to lose the NEJM study were underreporting.
>8 of the 9 were grossly underreporting.

The NEJM study has a number of loose ends that should be understood.

		DOUBLY LABELED WATER METHOD

The centerpiece of the study is the "doubly labeled water" (DLW)
method for which was claimed to have an accuracy of +- 5 per
cent.  To the uninformed, this appears to mean that measurements
made with this method will fall within 5 per cent of reality, as
one would expect when using a bathroom scale with a 5% rated
accuracy.  In fact, the 5% refers to the AVERAGE precision; some
readings will exceed this error.

DLW measures the disappearance of the components of water that
includes deuterium and 18 weight oxygen.  The idea is that the
body loses H2O as urine, sweat, etc., and oxygen in the form of
carbon dioxide from metabolism.  By measuring the disappearance
of deuterium and oxygen-18 we can observe the entrails of a
number of processes, one of which is the body's total metabolism (EE).

Of course few things are all that simple, and DLW requires a few
fudge factors to obtain "reasonable" numbers.  The accuracy of
EE measurement depends on the nature of the organism studied.
The DLW method over-reports EE in some organisms by as much as
50 per cent or more.  The papers validating DLW cited by the
NEJM article suggest an over-reporting bias on human males of
three percent error for each increment of BMI above 23.  Data
was not available to allow calculation of a correction factor
for females.

It is unfortunate that data on individual subjects were not
disclosed; with a sample size of only 10, conservation of ink
and page space was not the motivating factor.

The average BMI of the diet resisters was 34, so a correction of
30 per cent is called for.  This reduces the under-reporting of
energy intake from 47% to 17%, a figure comparable to that of
non obese subjects.  Without the correction, only three of the
subjects were consuming more than the 2200 kcal/d average energy
input for females (U.S.  Government data quoted in Consumer
Reports), and one of the subjects was a male!

As shown in the 3rd panel of figure 2, all but three of the 10
were in substantial energy imbalance, enough to gain or lose
a pound a week.

		EE PER UNIT OF FAT FREE MASS

The NEJM paper argues against a metabolic defect in the diet
resisters by noting that their resting metabolic rate (RMR) and
total energy expenditure (EE) are roughly proportional to fat
free mass.  Such an intellectual maneuver should be reassuring
to fat people who have been warned that their weight strains their
body.  "There should be no doubt that simply walking, climbing
stairs, or pumping blood through all of the excess tissue is a
form of exercise." (IJO 1989;13;s2 17)  A study of energy
requirements of dieting men found that replacing lost body
weight with equivalent lead weights reduced the fall in energy
expenditure by more than 50%.  Adipose tissue is more active
than either lead weights or many components of FFM, so
normalizations based on other than total weight must be regarded
with cynicism.

What arguments do nutritionists use to justify normalizing RMR
and especially EE by FFM?  None, really, except that it fits the
observed data!  That's about as useful as saying "Johnny flunked
reading because he can't read" without analyzing WHY Johnny
can't read.  The real reason is that normalizing EE by FFM hides
the association between low energy expenditure and many forms of obesity.

		LIARS, DAMM LIARS, and STATISTICIANS

It is interesting to note that the mean number of diet attempts
in the 10 diet resisters was 8 with a standard deviation of 7,
yet several (3-5) had as many as 20 serious attempts.

It is interesting to note that the diet resistant subjects had a
lower BMI but higher percent of fat than the other subjects.
Diet resisters had on average twice as many diets, and the
higher BMI / %fat ratio suggests the high cyclers lean body mass
had been reduced by diet cycling.  It could also mean there
weren't enough subjects to properly test for much of anything.

-- 
Chuck Forsberg WA7KGX          ...!tektronix!reed!omen!caf 
Author of YMODEM, ZMODEM, Professional-YAM, ZCOMM, and DSZ
  Omen Technology Inc    "The High Reliability Software"
17505-V NW Sauvie IS RD   Portland OR 97231   503-621-3406