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Weight loss and exercise: What works and what doesn't?
This article is biased.
It is heavily influenced by my experience as a personal trainer
in the early 1990's. During that time, I saw literally hundreds
of people try — and fail — to speed up weight
loss with a program of regular aerobic exercise.
By aerobic exercise, I mean things like cycling, walking, rowing
or jogging, usually performed for between 20 and 60 minutes in the
so-called "aerobic training zone." Interval exercise,
on the other hand, especially when you get the length
of the work and rest intervals right, is another story entirely.
Despite what we've been told, aerobic exercise has very little
effect on weight loss. There's been enough research over the last
25 years to convince almost anyone that aerobic exercise programs
are not a very effective way to promote weight loss.
Weight loss
Most people begin an exercise program designed for weight loss
with the intention of sticking with it. Unfortunately, the majority
give up after six months, deciding they simply don't have the time
to exercise regularly.
There are usually two reasons behind any decision — the real
reason, and the one that sounds good! Individuals claiming, "they
don't have the time" are often hiding the fact that their expectations
were not met. Simply put, they were not making the progress they
were promised. For many people, the benefits of aerobic exercise
are not enough to justify the time and effort you put in.
On an intellectual level, most people know they "should do
more exercise." However, any good salesperson will tell you
that we don't make decisions based on intellectual reasoning. We
base them on emotion.
Most of us exercise because, at a very basic level, we want to
look and feel better. We exercise because it appeals to our sense
of vanity and pride. We want to look and feel good.
The problem comes when there is a conflict between the results
you expect from aerobic exercise, and what you actually get.
Many people starting an exercise program are told they can expect
to lose around two pounds of fat each week.
Some people do. But the majority doesn't.
It's easy to think the problem lies with you. Is it because your
metabolism is slow? Are you getting older and burning calories at
a slower rate? Is it in your genes? You stick to the program, and
still you don't lose any weight.
What's going on?
Although it comes as a surprise to many, the majority of research
shows that aerobic exercise has only a minor effect on weight loss.
Some evidence for this comes from a review of several hundred weight
loss studies conducted by Dr. Wayne Miller and colleagues at The
George Washington University Medical Center [5].
The team examined 493 studies carried out between 1969 and 1994.
Miller and his associates wanted to determine whether adding aerobic
exercise to a low-calorie diet accelerates weight loss. Twenty-five
years of weight loss research shows that diet and aerobic exercise
provides only a very marginal benefit (in terms of weight loss)
when compared to diet alone.
The average weight loss after a 15-week program of regular aerobic
exercise was seven pounds. Over the same period, dieting cut weight
by roughly 17 pounds. When exercise and diet were combined, average
weight loss was 20 pounds — just three pounds more than diet
alone.
A study completed at Appalachian State University also shows that
aerobic exercise has little effect on body composition over a 12-week
period [7].
The research team assigned a group of 91 obese women to one of
four groups. Group one followed a restricted calorie diet (1,200
- 1,300 calories per day), while group two performed aerobic exercise
for 45 minutes, five days each week. A third group combined exercise
and diet. The fourth group acted as controls.
The exercise-only group lost just three pounds. This is despite
the fact they were exercising for almost four hours each week. Not
surprisingly, the women combining diet and exercise got the best
results, losing 16 pounds of fat. However, this was only one pound
more than the group on the diet. These disappointing results led
the researchers to conclude that aerobic exercise has only a "minor,
nonsignificant effect" on fat loss.
A study at Pennsylvania State University shows similar results
[10]. A group of men took part in a 12-week program of diet and
exercise. Half the men dieted, while the rest used a combination
of diet and aerobic exercise. Despite the fact they trained three
times each week for up to 50 minutes (under the watchful eye of
certified personal trainers), the exercise and diet group lost only
one pound more fat than the diet-only group.
Research carried in the Journal of Applied Physiology also
shows that aerobic exercise has a minor effect on fat loss [21].
A group of 24 obese men was assigned to either a low- or high-intensity
exercise group for 12 weeks. The men were told to maintain their
dietary habits during the study.
The exercise program consisted of cycling at either low-intensity
(40% VO2max) or high-intensity (70% VO2max) three times per week.
Each workout burned about 350 calories. The duration of each workout
for subjects in the low-intensity and high-intensity training program
was 57 and 33 minutes, respectively.
After analyzing the results, the researchers conclude that exercise
training "did not lead to significant changes in body weight
and body composition."
Aerobic exercise again failed to deliver any meaningful results
when the training frequency was increased to five times per week.
A team of Canadian researchers, publishing their findings in the
Journal of Applied Physiology, followed a group of men and
women for four months [16]. Half the group followed a restricted
calorie diet, while the rest combined the diet with five days a
week of cross training (a mixture of treadmill walking, cycling
and stepping).
At the end of the program, scientists were at a loss to explain
why the diet and exercise group had lost just one-half pound more
than the diet-only group, describing their findings as "perplexing".
In one 1997 study carried in the journal Medicine and Science
in Sports and Exercise, group of adult males lost just four
pounds in weight — despite three hours of exercise every week
for 14 weeks [11]. Hardly the dramatic results we're promised when
joining a gym.
Many people believe they need to spend six hours or more in the
gym each week to get the results they're looking for [9]. And it's
true that for aerobic exercise to be effective, you need to do a
lot of it. Scientists from Canada report that three months of aerobic
exercise was enough to cut body fat levels by an average of 13 pounds
[15]. However, the brave souls who volunteered for this study trained
for more than one hour, every single day, for three whole months.
Personally, all that aerobic exercise would bore me silly. The
exercise program I use to shed fat requires that I spend no more
than five hours in the gym each week. It's virtually identical to
the program you'll read about elsewhere
on this site. That's not because I'm lazy. It's just that I
don't have the time (or the motivation) for the marathon workouts
that all the "experts" tell me I need.
One of the main criticisms of weight loss studies is the small
number of participants they use. The more people that take part
in a study, the more reliable the results. The challenge for researchers
is trying to stop people dropping out. When a research group from
the University of Georgia attempted to examine the effect of aerobic
exercise on fat loss, more than half the subjects quit before the
study was finished [12]!
This shouldn't come as a surprise, especially when you consider
the fact most subjects make such little progress.
In an attempt to make their study more reliable, researchers designed
the HERITAGE Family Study, describing it as the largest, well-controlled
training study of its kind [13]. A large group of 557 men and women
was followed as they embarked on a 20-week exercise program.
Each subject was required to exercise three times per week for
an average of 42 minutes. Researchers even went to the trouble of
having each bout of exercise monitored by an exercise technician
and a computer. Following a grand total of 60 exercise sessions
over a period of almost six months, the average amount of fat lost
was slightly less than two pounds, prompting scientists to admit
that aerobic exercise "is not a major factor" in weight
loss.
Calorie counters
This isn't surprising when you consider how many calories are contained
in a pound of fat — the equivalent of roughly 3,555 calories.
The most fundamental aspect of any fat loss program is to create
a calorie deficit — to burn more calories than you eat. Unfortunately,
aerobic exercise burns around 187 calories per session [7]. Based
on this estimate, you'll need 19 workouts, each lasting 45 minutes,
to lose just one pound of fat.
This figure might come as a surprise if you use the calorie counters
on exercise machines to monitor calorie expenditure during a workout.
Unfortunately, these digital readouts are not always accurate. The
most reliable way to assess energy expenditure during exercise is
to measure oxygen consumption. Each liter of oxygen that you consume
generates approximately five calories of energy.
For example, if you exercise for 30 minutes and consume 30 liters
of oxygen, you'll have burned 150 calories. Without directly measuring
oxygen consumption, it's difficult to get an accurate estimate of
energy expenditure during a workout.
Another factor that affects the reliability of calorie counters
is the difference between net and gross calorie expenditure.
Gross energy expenditure refers to the number of calories
you burn during exercise plus your metabolic rate. Net
energy expenditure refers to just the number of calories
you burn during exercise.
Because calorie counters on some (but not all) exercise machines
display gross energy expenditure, the figures they give can
be misleading.
A good example comes from a trial carried in the International
Journal of Sport Nutrition [7]. A group of overweight women
took part in an aerobic exercise program. The program involved 45
minutes of aerobic exercise, performed in the so-called aerobic
training zone (70-80% of maximum heart rate).
The average number of calories burned during each workout was estimated
to be 255 calories. However, this figure doesn't take into
account the difference between net and gross caloric
expenditure.
The gross number of calories burned was 255. In contrast, the net
figure (remember, the net figure represents the "real"
number of extra calories you've burned) was just 187 calories. In
other words, if you rely on the numbers given by the calorie counters,
it might appear that you've burned more calories than you
really have.
Muscle loss
When you lose weight from dieting alone, some of the weight lost
comes from lean muscle tissue. Some experts believe that aerobic
exercise prevents this reduction in muscle mass. But the facts
tell a different story. Several studies show that diet and aerobic
exercise both lead to a drop in muscle tissue [10, 15]. Aerobic
exercise won't offset the loss in lean muscle caused by dieting.
When you lose weight by dieting, roughly seven of every 10 pounds
lost over a 12-week period come from fat. Adding aerobic exercise
doesn't prevent the loss of muscle. But it does reduce it slightly.
You'll get better results when you combine the right diet with aerobic
exercise and resistance training. Virtually all of the weight you
lose with this kind of program will come from fat [10].
One popular claim is that aerobic exercise leads to an increase
in your metabolic rate. However, researchers conducting the HERITAGE
Family Study found that almost six months of aerobic exercise has
no effect on resting metabolic rate [13].
Some studies do show that elite athletes do have a higher metabolic
rate than weight-matched controls. However, scientists have been
unable to establish whether this is due to a high calorie intake,
a superior level of fitness or if it exists simply as an after effect
of their last training session [6]. Furthermore, when an increase
in physical activity results in a calorie deficit, there is evidence
to show that the metabolic rate does not rise at all [6, 14].
Another popular misconception is the idea that aerobic exercise
increases caloric expenditure after a bout of exercise, thus
making a further contribution to fat loss. Unfortunately this is
not always the case. Excess post-exercise oxygen consumption (the
name given to the increase in caloric expenditure following a workout)
is more likely to occur after high-intensity exercise. Moderate-intensity
aerobic exercise (such as walking or jogging) has very little effect
on post-exercise metabolic rate.
Does this mean that aerobic exercise is a waste of time? Definitely
not.
Weight gain
There is evidence to show that aerobic exercise helps to prevent
the gain in weight that often happens following a period of dieting
[2]. It's extremely difficult to stick to the kind of diet needed
to maintain weight loss. As a result, many people soon return to
their original weight.
Aerobic exercise plays a vital role in helping you maintain a healthy
body weight. The National Weight Control registry contains a listing
of subjects who have lost at least 30 pounds of weight, and kept
it off for at least 12 months.
Although the people on the register use a number of different strategies
to reduce body fat, the one thing they have in common is a commitment
to regular exercise [4]. Scientists from George Washington University
also report that regular exercise helps to maintain higher levels
of weekly fat loss 12 months after starting a diet [5].
Researchers at Maastricht University have shown that just ten weeks
on a very low-calorie diet actually reduces the number of fat calories
your body burns each day [8]. This post-diet drop in fat oxidation
could explain why many people find it difficult to stop the weight
coming back once they've lost it.
A group of 40 overweight men took part in the study. They were
assigned to one of two groups. One group dieted, while group two
combined the diet with a program of regular aerobic exercise. The
men in the exercise group completed three sessions per week, consisting
of walking and underwater exercise. Each workout lasted for around
one hour.
During the first six weeks of the study, subjects in both groups
were given a very low-calorie diet providing just 500 calories daily.
From weeks 7 to 10, they gradually increased their food intake.
Both groups lost roughly the same amount of fat and muscle. However,
the subjects who didn't exercise had a reduced capacity to burn
fat, both at rest and during exercise. The good news is that exercise
served to prevent this decline.
What this means is that the benefits of low-intensity aerobic exercise
are more apparent when you're trying to keep the weight off. The
exercise doesn't have to be particularly vigorous or demanding.
Just three hours of walking each week is enough to prevent the post-diet
decline in fat oxidation.
Physical activity as part of a fat loss strategy also appears to
encourage healthier eating patterns. Individuals who exercise frequently
may perceive food as "activity fuel", and place greater
importance on the quality of their diet.
Californian researchers have identified a direct link between physical
activity and various markers of dietary quality [3]. They found
that physical activity was associated with healthy eating habits,
such as eating fruit and vegetables. More physically active individuals
are also less likely to eat foods with a high calorie content.
That said, there are also people who eat what they want, then
do hours and hours of exercise in an attempt to burn it off again.
This is mistake. When it comes to shedding fat while preserving
lean muscle, one of the most important hormones is testosterone.
Although testosterone is considered a muscle-building hormone,
there are studies showing that it also helps to cut body fat.
Unfortunately, too much exercise can lower testosterone. Endurance-trained
men, for example, have lower testosterone levels than men of the
same age who never exercise [19]. Men with low
testosterone levels are also more likely to develop a pot belly
[17].
In short, trying to make up for a poor diet by doing a lot of aerobic
exercise is not a good idea.
Subcutaneous fat
Publishing their findings in Medicine and Science in Sports
and Exercise, Japanese researchers have shown that dieting leads
to a greater reduction in visceral fat [1]. Exercise, on the other
hand, has a greater impact on subcutaneous fat. Subcutaneous fat
(pronounced sub-cue-tain-ee-us) is stored just under your skin.
Visceral fat (pronounced viss-er-al) surrounds and protects
your internal organs.
The women in the study took part in a 13-week program that combined
exercise with a restricted-calorie diet. One group followed the
diet, combined with 1-2 days per week of exercise. Group two made
no change to their diet, but exercised 3-4 days each week.
Both groups lost roughly the same amount of fat. In the group who
exercised more frequently, six of every 10 pounds of fat lost came
from subcutaneous fat. However, in the group who exercised less
frequently, less than three of every 10 pounds of fat lost came
from subcutaneous fat.
Energy flux
Aerobic exercise also allows for a higher energy flux, which refers
to the flow of calories (or energy) through your body.
A high energy flux means that you're eating a large number of calories,
but balancing that with an equally high volume of exercise. A good
example of someone with a high energy flux would be a cyclist taking
part in the Tour de France. Despite the fact these athletes eat
thousands of calories each day, they're still able to remain lean
simply because they're doing so much exercise.
An example of a low energy flux would be someone following an extremely
low-calorie diet while doing little or no exercise.
A high energy flux is linked with a high metabolic rate. Endurance-trained
males, for example, in a high state of energy flux have a higher
metabolic rate compared with a low energy flux state.
As they age, people are generally less physically active. The result
is that they burn fewer calories each day. Unless they eat less
to compensate for this reduction in calorie expenditure, weight
gain is the inevitable result.
The good news is that you can minimize the age-related drop in
basal metabolic rate by maintaining a high energy flux — balancing
a higher calorie intake with an equally high volume of exercise.
Not only will this help you to stay lean, it's also a great way
to provide your body with more of the vitamins, minerals and other
nutrients it needs.
The bottom line
Many people starting an exercise program are told they can expect
to lose around two pounds of fat each week. Some people do. However,
the majority doesn't.
It's easy to think the problem lies with you. Is it because your
metabolism is slow? Are you getting older and burning calories at
a slower rate? Is it in your genes? You stick to the program, and
still you don't lose any weight.
Although it comes as a surprise to many, the majority of research
shows that aerobic exercise — such as waking, jogging, cycling
or rowing — in the so-called "aerobic training zone"
is not a very effective way to lose fat.
At best, you can expect to lose between one-quarter and one-half
pound of fat per week, depending on how much aerobic exercise you
do.
Regular exercise is important because it promotes the loss of subcutaneous
fat. Subcutaneous fat is stored just under your skin. Visceral
fat surrounds and protects your internal organs.
Aerobic exercise also allows for a higher energy flux, which refers
to the flow of calories (or energy) through your body. This lets
you balance a higher calorie intake with an equally high volume
of exercise. Not only will this help you to stay lean, it's also
a great way to provide your body with the vitamins, minerals and
other nutrients it needs.
References
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