Science Center: Increasing Your Metabolism
By The Weight Watchers Research Dept. | 3/31/2005


When it comes to weight loss, it's all about calories. Burning more
calories than the body takes in results in weight loss and taking in
more calories than are burned means a weight gain.

Metabolism is the number of calories the body burns and is made up of
three components: resting metabolic rate, physical activity and a
small amount needed for food digestion. Increasing the body's
metabolism has the potential to enhance weight management because the
number of calories needed each day would be higher (and so the amount
of food needed to fuel that need would be greater).

While many popular publications would lead you to believe otherwise,
metabolism can only be boosted in two ways: increasing the body's
muscle mass and increasing the body's heart rate.

Muscle Mass
Losing some muscle mass is considered to be an expected part of
weight loss because a smaller body needs less muscle to move the
body's weight around. Resistance (i.e., weight) training as part of a
comprehensive exercise plan can increase lean muscle mass in weight-
stable individuals and minimize loss of lean tissue during weight
loss. While a few studies have demonstrated otherwise, most studies
show that it is not feasible to decrease body weight and
simultaneously increase lean muscle tissue. 1

A popular theory concerning weight loss, increased metabolism and
exercise states that it is feasible to create a sustained increase in
metabolism through regular aerobic workouts. The studies that have
evaluated this theory for scientific merit have shown very mixed
results. The general finding for studies done in humans is that, if
this phenomenon exists, the impact on overall metabolism is very
small. 2 Further, there are no studies that have directly linked
the "after effects" of exercise with significant weight loss.

Heart Rate's Impact
A person's heart rate has an impact on metabolism – the higher the
heart rate, the more calories burned. Stimulants, whether from a
prescribed medication, dietary supplement, or a caffeine-containing
beverage, all work to increase the heart rate and fire up the nervous
system.

In a controlled study that looked at giving stimulants, including
amphetamines or a placebo, weight loss was greater with the stimulant
because heart rate and blood pressure were raised and food intake was
decreased as a side effect of being "hyper." 3

Most dietary supplements and herbal compounds that are sold over the
counter to promote weight loss contain stimulants, though at a lesser
strength than that found in amphetamines. These products are often
marketed as having "fat burning" properties, which are achieved
because they increase heart rate and blood pressure and decrease
appetite. They can work, but they do so at a cost to the body.
Negative side effects include insomnia, nervousness, anxiety and, in
extreme cases, death.

Increasingly, some of these products (including the ones that were
most effective, like fen-phen and ephedra) have been banned because
of their negative side effects.