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September 2011, Week 4

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Mon, 26 Sep 2011 01:07:07 -0400
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(1)
Weight Loss through Cutting Calories Results Less 
than Expected
Diet, Obesity, Prevention, Issue 589
This article originally posted 01 September, 2011
http://www.diabetesincontrol.com/index.php?option=com_content&view=article&id=11423

Common rules of thumb exaggerate how much weight people
will lose from a given dietary calorie reduction,
leading to unrealistic expectations and disappointment,
researchers said....

According to Kevin D. Hall, PhD, of the National
Institute of Diabetes and Digestive and Kidney Diseases
in Bethesda, Md, whereas patients are often told that
cutting 500 calories a day will let them lose a pound a
week, a more realistic formula is that such a caloric
reduction would lead to a 50-pound loss over three or
more years.

Even then, such weight loss is possible only if the
calorie reduction is actually maintained over that time.
The standard rules -- endorsed by the National
Institutes of Health and the American Dietetic
Association, among others -- fail to consider that human
metabolism responds dynamically to changes in diet and
body composition, Hall and colleagues asserted.

If a 300-pound dieter could really lose a pound a week
by cutting his regular diet by 500 calories, he would
vanish entirely in six years.

"This ubiquitous weight-loss rule (also known as the
3,500 [calorie]-per-pound rule) was derived by
estimation of the energy content of weight lost, but it
ignores dynamic physiological adaptations to altered
body weight that lead to changes of both the resting
metabolic rate as well as the energy cost of physical
activity," the researchers wrote.

When people gain weight, their baseline energy needs
increase, to keep the extra tissue alive and to move it
around. Likewise, when weight is lost, their baseline
needs decrease.

So when people cut calories below the baseline
requirement -- thereby triggering weight loss -- the gap
between their intake and their baseline energy needs
begins to shrink. At some point, it may disappear
altogether, at which point weight loss stops.

Hall and colleagues put together what they said was a
better model of caloric intake and resultant weight
loss, incorporating feedback mechanisms to reflect
metabolic changes over time in response to diet and body
weight. It indicated that weight change in response to
caloric restriction occurs over a relatively long period
of time.

Each reduction of 100 kilojoules daily -- 24 calories --
in intake eventually leads to a loss of 1 kg (2.2 lbs)
in body weight, the researchers determined. But only
half that loss occurs in the first year. In three years,
95% of the ultimate loss will be realized.

On the flip side, using data from previous studies, Hall
and colleagues said their calculations suggest that the
U.S. population has a persistent excess energy intake of
30 kilojoules (7.2 calories) per day, explaining the
increasing prevalence of overweight and obesity.

For the population to return to body mass index values
that prevailed in the 1970s, average diets would need to
shrink by about 220 calories per day.

The researchers pointed out that these figures are
averages for the adult population. Individuals'
metabolic requirements for sustaining a given body mass
vary substantially. Consequently, "a given diet results
in an uncertain degree of energy deficit," Hall and
colleagues wrote.

The findings have important implications for policy, the
researchers argued.

For example, they pointed to a 2010 policy paper from
the U.S. Department of Agriculture, which included an
estimate that a 20% tax on sugar-sweetened drinks would
reduce average energy intake by 40 calories. Using the
standard 3,500 calorie-per-pound rule, the paper
indicated that an average weight loss of about 1.8 kg (4
lbs.) per year could be expected -- "incorrectly," Hall
and colleagues contended. Their model shows that it
would actually take five years to achieve that level of
average weight loss.

"We suggest that unrealistic weight loss expectations
obtained by erroneous use of the static dieting rule
should be replaced by our methods to assess other
population-wide and more targeted obesity prevention
interventions," the researchers wrote.

They also pointed out that, in evaluating interventions,
the model can also take account of physical activity and
its effects on body weight and metabolism.

On the other hand, a limitation is that "it assumes
perfect adherence to the intervention" and also doesn't
automatically include increases in food intake that may
accompany the start of an exercise program.

The problem, of course, is that adherence is usually
anything but perfect. Moreover, it can be compounded by
the long lag between changes in diet and changes in body
weight.

One manifestation is that patients lose weight while on
a program and continue to do so -- for a time -- after
they revert to their former lifestyle. "The dieter might
then incorrectly infer that adherence is not essential
for continuing weight loss when, in fact, impending
weight regain has already been set in motion," the
researchers indicated.

Practice Pearls:

Explain that a study using mathematical modeling
explains that weight loss and energy intake reduction
are not static processes and require much more time than
previously appreciated.

Point out that the formula predicts only 50% of weight
loss within the first year and 95% by three years with a
consistent calorie reduction.

Hall K, et al "Quantification of the effect of energy
imbalance on bodyweight" Lancet 2011; 378: 826-37.


(2)
Quantification of the Effect of Energy Imbalance 
on Bodyweight
Dr Kevin D Hall PhD a , Gary Sacks PhD b, 
Dhruva Chandramohan BSc a, Carson C Chow PhD a, 
Y Claire Wang MD c, Steven L Gortmaker PhD d, 
Boyd A Swinburn MD b
The Lancet, Volume 378, Issue 9793, Pages 826 - 837
27 August 2011
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2811%2960812-X/abstract

Summary

Obesity interventions can result in weight loss, but
accurate prediction of the bodyweight time course
requires properly accounting for dynamic energy
imbalances. In this report, we describe a mathematical
modelling approach to adult human metabolism that
simulates energy expenditure adaptations during weight
loss. We also present a web-based simulator for
prediction of weight change dynamics. We show that the
bodyweight response to a change of energy intake is
slow, with half times of about 1 year. Furthermore,
adults with greater adiposity have a larger expected
weight loss for the same change of energy intake, and to
reach their steady-state weight will take longer than it
would for those with less initial body fat. Using a
population-averaged model, we calculated the energy-
balance dynamics corresponding to the development of the
US adult obesity epidemic. A small persistent average
daily energy imbalance gap between intake and
expenditure of about 30 kJ per day underlies the
observed average weight gain. However, energy intake
must have risen to keep pace with increased expenditure
associated with increased weight. The average increase
of energy intake needed to sustain the increased weight
(the maintenance energy gap) has amounted to about 0ยท9
MJ per day and quantifies the public health challenge to
reverse the obesity epidemic.

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