24
remarkable leaps in TMR and heat production. When a well-
trained athlete exercises vigorously for several minutes, TMR
may increase 20-fold and remain elevated for several hours aFer
exercise stops.
±ood ingestion also induces a rapid increase in TMR. ²is
effect, called
food-induced thermogenesis
, is greatest when
proteins and alcohol are ingested. ²e heightened metabolic
and voluntary. BMR accounts for a surprisingly large part of
TMR. ±or example, a woman whose total energy needs per day
are about 2000 kcal may spend 1400 kcal or so supporting vital
body activities.
Skeletal muscles make up nearly half of body mass, so skele-
tal muscle activity causes the most dramatic short-term changes
in TMR. Even slight increases in muscular work can cause
“apple”) associated with heart disease
and diabetes mellitus. (This propensity
to these diseases, called “metabolic
syndrome,” appears to be due to
the large amounts of inflammatory
cytokines released by visceral fat cells.)
When dieting continued for a year,
those on the low-fat diets lost just as
much weight as did those on the low-
carbohydrate diets. Although there was
concern that the low-carbohydrate diets
would promote undesirable plasma
cholesterol and lipid values, for the most
part this has not been the case.
Diets that have users counting the
glycemic indexes of the food they eat,
such as the New Glucose Revolution
diet, distinguish between good carbs
(whole grains, nonstarchy vegetables
and fruits) and bad carbs (starches,
sugary foods, refined grains). Many
physicians approve.
The oldie-but-goodie Weight
Watchers diet, which has dieters
counting points, still works and allows
virtually any food choice as long as the
allowed point count isn’t exceeded.
Some over-the-counter liquid
high-protein diets contain such poor-
quality (incomplete) protein that they
are actually dangerous. The worst are
those that contain collagen protein
instead of milk or soybean sources.
3. Surgery.
Sometimes sheer desperation
prompts surgical solutions: reducing
stomach volume by banding; gastric
bypass surgery, which may involve
stomach stapling and intestinal
bypass surgery, or the more radical
biliopancreatic diversion (BPD); and
liposuction (removing fat by suctioning).
BPD rearranges the digestive tract.
The surgeon removes up to two-thirds
of the stomach and cuts the small
intestine in half, suturing one portion
to the stomach opening. This diverts
pancreatic juice and bile away from the
“new intestine,” so far fewer nutrients
and no fats are absorbed. Patients
can eat anything they want without
gaining weight, but exceeding the
stomach capacity leads to the dumping
syndrome (nausea and vomiting).
Many BPD procedures have been
remarkably effective at promoting
weight loss and restoring health. Blood
pressure returns to normal in many who
were originally hypertensive, and sleep
apnea is reduced. Additionally, up to
86% of patients with long-standing
type 2 diabetes mellitus find they are
suddenly diabetes free or demonstrate a
dramatic improvement in their regulation
of the disease within weeks after the
procedure. This result may prove to be
the single greatest benefit of BPD.
Liposuction reshapes the body by
suctioning off fat deposits, but it is
not a good choice for losing weight.
It carries all the risks of surgery, and
unless eating habits change, fat depots
elsewhere in the body overfill.
4. Gastrointestinal liners.
A GI
liner, which prevents food from
contacting the first 20 inches or
so of the intestinal wall, is inserted
endoscopically through the mouth.
Nutrients are still absorbed beyond the
liner but in obviously reduced amounts.
This device seems to help some obese
individuals lose weight.
5. Diet drugs and weight-loss
supplements.
Currently popular
weight-loss drugs include phentermine,
phendimetrazine, diethylpropion, and
orlistat. Phentermine is one-half of the
former fen-phen (Redux) combination
that caused heart problems, deaths,
and litigation for its producer in the
1990s. It acts by increasing sympathetic
nervous system activity, which raises
blood pressure and heart rate and
decreases hunger. Phendimetrazine and
diethylpropion have amphetamine-like
effects, stimulating the central nervous
system to increase heart rate and blood
pressure and decrease hunger.
Orlistat (Xenical) interferes with
pancreatic lipase so that part of the
fat eaten is not digested or absorbed,
which also interferes with the
absorption of fat-soluble vitamins. It is
effective as a weight-loss agent, but its
side effects (diarrhea and anal leakage)
are unpleasant to say the least. It also
carries the risk of severe liver injury.
Currently a number of drugs
are being developed that act at
several different CNS sites, including
neuropeptide Y inhibitors.
Several over-the-counter weight-
loss supplements that claim to increase
metabolism and burn calories have proved
to be very dangerous. For example:
Capsules containing usnic acid, a
chemical found in some lichens,
damages hepatocytes and has led to
liver failure in a few cases.
Ephedra-containing supplements
are notorious—over 100 deaths and
16,000 cases of problems including
strokes, seizures, and headaches
have been reported.
When it comes to supplements, the
burden of proof is on the U.S. FDA to
show that the product is unsafe. For
this reason, the true extent of problems
caused by weight-loss supplements
is not known—while the worst cases
attract attention, less serious ones go
unreported or undiagnosed.
So are there any good treatments for
obesity? To be absolutely honest—not yet.
However, animal studies have shown that
activating brown fat counteracts weight
gain and type 2 diabetes. The possibility
that activated brown adipose tissue could
deter or reverse obesity is definitely worth
exploring.
At present, the only realistic way to
lose weight is to take in fewer calories and
increase physical activity. Fidgeting helps
and so does resistance exercise, which
increases muscle mass. Physical exercise
depresses appetite and increases metabolic
rate not only during activity but also for
some time after. The only way to keep the
weight off is to make dietary and exercise
changes lifelong habits.
A CLOSER LOOK
(continued)
943
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