The Exercise “Myth” for Weight Loss
"The Exercise “Myth” for Weight Loss" When trying to lose weight,
which is more important: diet or exercise? A national survey found that
a "vast majority" of Americans trying to control their weight believed that food
and beverage consumption and physical activity
were equally important. Seven out of ten
went with equally important, about two out of ten thought
exercise was more important, and only about one
out of ten chose diet. The vast majority of Americans
are wrong. It's easy to understand
how people might think diet and exercise
play equal roles. After all,
our weight is determined by the balance of calories in
and calories out. What people may not understand about this
energy balance equation is we have much more power
over the "calories in" side.
In fact, on a day-to-day basis
we have full control, we could choose
to eat zero calories or 10,000 calories. But most of the "calories out" tend to be outside
of our control. Unlike wild animals
who tend to burn most of their calories
on activity, about 60 percent
of our daily calories are used up
just to keep us alive, what's called our resting,
or basal, metabolic rate, thanks in part
to our energy-intensive brains. Even if you stayed in bed
all day, you'd still burn
more than 1,000 calories just to fuel the basics
like thinking, breathing, keeping your heart pumping. In contrast,
even most "active" people accrue less than two hours
of exercise a week, which may average out
to be less than 100 calories burned off each day.
That's only about 5 percent of the total
daily energy expenditure, the "calories out" side
of the equation. So, the 2,000 calories we may
take in every day from our diet can exert 20 times
more influence than exercise over our weight destiny. Most people believe that
exercise is "very effective" as a way to lose weight, but this has been
referred to as a myth in the scientific literature. In fact, it's been labeled one of the most common
misconceptions in the field of obesity. Yet virtually all
formal weight-loss guidelines include some sort of physical
activity recommendation. Can you outrun a bad diet? Let's see what the science says. Population studies
have certainly found strong correlations between
physical inactivity and obesity. But does a sedentary lifestyle
lead to obesity, or does obesity lead
to a sedentary lifestyle? It probably works a little bit
in both directions. To prove cause and effect, and also quantify
the relationship, you really have to put it
to the test.
Dozens of randomized
controlled trials involving thousands
of participants have been published
on the effects of exercise on weight loss. Physical activity was not found
to be an effective strategy. For example,
if you look at the studies that tried using exercise alone
to induce weight loss, over an average
of about five months, people only lost
about three pounds. When you put
all the studies together, it looks like it took
around six weeks of exercising to get people
to lose a single pound. That was exercise alone, though. What about as an adjunct
to diet? If you randomize people into a diet
and exercise intervention versus just the diet alone, the added exercise group
does do better, but the difference
in weight loss only averaged about two pounds.
The studies lasted
between 3 and 12 months, and all of that
extra prescribed exercise only seemed to translate
into a few pounds. The two-pound difference
was statistically significant, which means we're pretty sure
it was a real effect, but losing two pounds
over a year's time can hardly be considered
clinically significant. As a general rule,
researchers like to see at least a five-
or six-pound drop. In a meta-analysis of 18
randomized controlled trials lasting a minimum
of six months, the diet-plus-exercise group failed to significantly beat out
the diet-only group at all. There appeared to be
no long-term benefit to encouraging people
to add exercise to their weight-loss regimen. What is going on? Maybe exercise is just better at preventing people
from regaining weight. No. The vast majority
of randomized controlled trials examining
weight-loss maintenance also failed to show
an exercise benefit. Part of the problem
is compliance. It's one thing
to tell people to adhere
to an exercise regimen; it's another thing for them
to actually do it.
When the same randomized
controlled trials were re-analyzed
to exclude people who flouted the instructions, and analysis was limited
to just those who actually put in
the time and sweat, a clear advantage
to exercise emerges. Exercise only works
if you actually do it, though one reason people
may become rapidly disillusioned with their new gym membership is their gross overestimation of the capacity of exercise
to burn off extra calories. A slice of pizza
has about 300 calories. That converts into an hour
of brisk walking per slice, an hour a slice! How many kids
are jogging two hours a day to burn off their happy meals? Who's got time to climb
50 flights of stairs to take care of the calories
in just one Oreo cookie? That's one of the reasons that what we put in our mouths
is most important.
Public health researchers
have been experimenting with including labeling
on junk food. Which label
is more informative? This one or these? Still want that Toblerone
if it means you have to walk two hours? Or cookies
you'd have to skip rope for 81 minutes for? I think I'd run an hour
just to avoid having to eat shrimp-flavored potato chips. Labeling fast food menus
with little pictograms of exercising stick figures
was found to help nudge people towards lower calorie options. Seeing that the decision
to supersize your fries would mean walking
an extra three miles that day or that choosing
the chicken salad over the garden salad
could mean having to run nearly three miles, people are more likely
to make the healthier choice..
