FOR IMMEDIATE RELEASE
September 2, 2009
Contact: Donna Krupa
Office: (301) 634-7253
commoff@the-aps.org
Exercise Minimizes Weight
Regain By Reducing Appetite, Burning Fat,
And Lowering ‘Defended’ Body Weight
BETHESDA, Md. (September 2, 2009) — Exercise
helps prevent weight regain after dieting by reducing appetite and by
burning fat before burning carbohydrates, according to a new study with
rats. Burning fat first and storing carbohydrates for use later in the day
slows weight regain and may minimize overeating by signaling a feeling of
fullness to the brain.
The University of Colorado Denver study also found that
exercise prevents the increase in the number of fat cells that occurs during
weight regain, challenging the conventional wisdom that the number of fat
cells is set and cannot be altered by dietary or lifestyle changes.
These coordinated physiological changes in the brain
and the body lower the ‘defended’ weight, that is, the weight that our
physiology drives us to achieve, and suggest that the effects of exercise on
these physiological processes may make it easier to stay on a diet.
The study is “Regular exercise attenuates the
metabolic drive to regain weight after long term weight loss.” Paul S.
MacLean, Janine A. Higgins, Holly R. Wyatt, Edward L. Melanson, Ginger C.
Johnson, Matthew R. Jackman, Erin D. Giles, Ian E. Brown and James O. Hill,
all of the University of Colorado Denver, conducted the study. The
American Physiological Society published the research in the American
Journal of Physiology – Regulatory, Integrative and Comparative Physiology.
How exercise works
Weight gain is, on the surface, remarkably simple,
occurring when the calories consumed exceeds the calories expended. On
closer examination, the process is remarkably complex. Laboratory, animals
eat according to physiological signals that may suppress appetite or arouse
the desire to eat. These signals are relatively weak in humans, as their
intake is largely influenced by psychological, cognitive and lifestyle
factors. After dieting, however, the physiological signals emerge to play a
more substantial role in controlling intake. Being persistently hungry
after losing weight with restricted diets is a big part of the weight regain
problem. Most people are unable to ignore this physiological cue and are
pushed by their biology to overeat and regain the weight they worked so hard
to lose.
Some people are successful at keeping the weight off,
and those tracked by The National Weight Control Registry share a number of
common characteristics, including a program of regular exercise. The aim of
this investigation was to uncover how exercise affects the body’s physiology
to minimize weight regain.
The researchers used obesity-prone rats. For the first
16 weeks, the rats ate a high-fat diet, as much as they wanted, and remained
sedentary. They were then placed on a diet. For the following two weeks, the
animals ate a low-fat and low-calorie diet, losing about 14% of their body
weight. The rats maintained the weight loss by dieting for eight more weeks.
Half the rats exercised regularly on a treadmill during this period while
the other half remained sedentary.
In the final 8-weeks, the relapse phase of the study,
the rats stopped dieting and ate as much low-fat food as they wanted. The
rats in the exercise group continued to exercise and the sedentary rats
remained sedentary.
Compared to the sedentary rats, the exercisers:
-
regained less weight during the relapse period
-
developed a lower ‘defended’ body weight
-
burned more fat early in the day, and more carbohydrates
later in the day
-
accumulated fewer fat cells and less abdominal fat during
relapse
-
reduced the drive to overeat
-
enhanced the ability to balance energy intake with energy
expended
During feeding, the sedentary group preferentially
burned carbohydrates while sending fat from the diet to fat tissue. This
preferential fuel use stores more calories because it requires less energy
to store fat than to store carbohydrates. In addition, burning away the
body’s carbohydrates may contribute to the persistent feeling of hunger and
large appetite of the sedentary animals.
Exercise blunted this fuel preference, favoring the
burning of fat for energy needs and saving ingested carbohydrates so that
they could be used later in the day. Taken together, the exercise led to a
much lower appetite and fewer calories ending up in fat tissue.
The researchers also found that exercise prevented the
increase in the number of fat cells observed with weight regain in sedentary
rats. In sedentary rats, a population of very small, presumably new, fat
cells appears early in the relapse process. Small, new fat cells would not
only accelerate the process of regain, but also increase fat storage
capacity in the abdomen. It would also explain why sedentary rats overshoot
their previous weight when they relapse.
Conventional wisdom holds that the number of fat cells
is determined by genetics, rather than being regulated by diet or lifestyle.
Because this effect of exercise is a novel finding, the team will do further
research to demonstrate that exercise is, indeed, preventing the formation
of new fat cells early in relapse and not simply altering the size of
pre-existing fat cells.
Editor’s Notes: To arrange an interview with Dr.
MacLean, please contact Donna Krupa (301) 634-7253 or at
commoff@the-aps.org.
To read the full study click
here or cut or paste the following link into your web browser:
http://ajpregu.physiology.org/cgi/reprint/297/3/R793
Physiology
is the study of how molecules, cells, tissues and organs function to create
health or disease. The American Physiological Society (APS) has been an
integral part of this scientific discovery process since it was established
in 1887.
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