You’ve probably
heard at some point that it takes a roughly 3,500-calorie
deficit between calories consumed and calories burned
to produce a one-pound drop in body weight. This old
chestnut is more than 60 years old and commonly cited
in scientific literature. Problem is, it’s not
exactly an accurate rule.
The 3,500-calorie rule
dates back to 1958, when Max Washnofsky, M.D., wrote
a paper in the American Journal of Clinical Nutrition
concluding “that 3,500 calories is the caloric
value of one pound of body weight lost.”
The number was simple,
stark, and capable of being reduced to 500 calories
per day multiplied by seven days a week to total 3,500
calories per week, or one pound of weight loss per
week. That’s why you also hear that healthy
weight loss for the average person is about four to
five pounds per month.
This all seemed logical
and even doable, so the 3,500-calorie rule stuck,
and prospered. Today, many conventional weight-loss
plans still tout the 500-calories-a-day approach.
This isn’t wrong—when oversimplified,
weight loss can boiled down to calories in need to
be less than calories out. But this approach won’t
work in the long term.
The 3,500-calories rule
is actually largely accurate if you’re burning
a pound of flesh in a chemistry lab. However, the
human body isn’t a lab, where you can isolate
and analyze one factor at a time and weight loss doesn’t
exist in a vacuum. Rather, the body is an organic
whole, and has many reactions to changes in calories,
carbohydrates, fats, proteins, metabolism, exercise,
hydration, and hormones.
When you’re making
a lifestyle change through diet, almost all these
interrelated events conspire to lower your daily metabolic
rate through a process known as “metabolic adaptation.”
As a result, a daily deficit of 500 calories produces
slightly less effect on each subsequent day. The difference
isn’t big at first, but grows substantially
with longer periods of time, producing just 50 percent
of the expected weight loss over 12 months.
“The biggest flaw
with the 500-calorie-rule is that it assumes weight
loss will continue in a linear fashion over time,”
says weight-change mathematician Kevin Hall, Ph.D.
“That’s not the way the body responds.
The body is a very dynamic system, and a change in
one part of the system always produces changes in
other parts.”
That’s why physiologists,
nutritionists, and researchers have since emphasized
that the 3,500-calorie-rule is an estimation that
doesn’t take into account the variety of factors
that affect weight loss over time.
What’s realistic?
According to Hall, in the first year of a new weight-loss
program, most people will lose about half the weight
that the 3,500-calories rule predicts. In other words,
over 12 months, instead of losing around 48 pounds,
the average person may lose around 24 pounds—if
that. And even still, this estimation largely depends
on the person, primarily assuming they have a significant
amount of weight to lose.
Individual weight losses
are highly variable. The most overweight people will
lose the most weight in the first few months of a
program; the leanest will lose the least. That’s
also why the “last five pounds” is always
the toughest. Once you get leaner, it’s more
difficult to lose additional weight—this is
our bodies’ natural survival mechanism.
Still, Hall believes
it’s better to succeed with an evidence-based
strategy than to fall short with the old, difficult-to-achieve
model. And evidence suggests that the best weight
loss plan is the one you can adhere to over the long
term, which tends to be less restrictive.
It’s important
to remember that counting calories is not the be-all-to-end-all
when it comes to weight loss. In fact, it can sometimes
create an unhealthy relationship with food and exercise.
Smartwatches, apps, and other calorie trackers are
available if you need them, but when you run regularly
and fill your plate with fresh, healthy options, you
know you’re doing the right things to keep your
body healthy—regardless of weight.
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