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Ever wonder why your body weight and general physique so seldom change? Most of us maintain
our weight within a small range and when you do the math, that is really quite remarkable.
An active adult takes in and expends about one million calories a year, but a continuing
positive imbalance of just 50 measly calories daily (that equals a few potato chips or
morsels of a sports bar) should, in theory, lead to a gain of 50 pounds in 10 years. Of
course, none of us monitors calories that closely, yet our weight doesn’t fluctuate with
every binge or missed meal.
Furthermore, when weight is lost, whether through illness or dieting, it’s almost invariably
regained. It’s as if the body knows where it wants to be and takes the necessary steps to
get there. Even animals regulate their weight. Underfed lab rats will lose weight. But as
soon as they’re given unlimited access to food, they overeat until their weight catches up
with their brothers and sisters who have never dieted.
What’s the answer to this conundrum? It’s been suggested that animals, including humans,
have a “natural” weight that is probably genetically determined, a phenomenon called
“set-point.” But here’s the important point: This weight varies from one individual to the
next. Some of us were born to maintain higher weights than others. When weight deviates
from this natural set-point, the body attempts to get things back to normal. In other
words, losing weight activates mechanisms that lead to weight gain, and vice versa.
How Does the Set-point Work?
In the last five to ten years, there’s been an explosion of research on body weight
regulation. A key discovery has been leptin, a molecule produced in fat cells and released
into the blood. Leptin is taken up by the brain where it activates processes that reduce
appetite. So according to the theory, as fat cells shrink during weight loss, they produce
less leptin, leading to less appetite reduction. The result? Food intake increases, fat
cells get bigger and produce more leptin as weight is gained. Appetite returns to normal
when the “set-point” is restored.
So Why Is Everyone Getting Fatter?
The set-point isn’t perfect—it can be overridden. Laboratory rats fed a normal diet rarely
become obese; their set-points function effectively. But if you provide them with unlimited
amounts of a high-fat, high-sugar “tasty” diet (similar to the food choices widely
available to humans today), many overeat and become obese. If they go back to their normal
(boring!) diet after a short period of time, they lose the excess weight. But—and this is
a large but—if they’re on the tempting diet for longer time periods, they don’t lose the
weight, even after returning to their normal diet.
This phenomenon has probably contributed to the recent epidemic of obesity in American
“humanimals.” We’re exposed to an ever-expanding cornucopia of tasty, convenient foods,
freely available 24 hours a day. And guess what? Between 1991 and 1998, obesity in the
U.S. increased from 12 to 18%. (In this study, obesity was defined as a Body Mass Index
over 30, equal to 186 pounds for a 5’6” person). Obviously, genetics can’t explain those
changes.
Can Exercise Adjust the Set-point?
It depends—increased activity in people already at their natural weight rarely leads to
weight loss—appetite usually increases, and weight is maintained. That’s why elite cyclists
and marathoners can put in massive miles without withering away. The good news, though, is
that in overweight people above their natural weight, exercise doesn’t seem to stimulate
appetite as much, and they may lose weight. Exercise also helps maintain any weight loss
that does occur.
Also, regardless of whether you lose weight with exercise, you’ll still be healthier if you
work out. Recent studies from the Cooper Clinic in Texas show that being “lean and unfit”
is actually a greater risk for heart disease and death than being “fat and fit.”
What About Food Choices?
Even if it would help maintain weight, most of us probably wouldn’t want to live on the
human version of rat chow. Nor should we—variety is a cornerstone of a healthy diet. But
eating more of your food in forms that Mother Nature provides might help your set-point do
its job. A recent study found that adults with higher fiber intakes gained less weight over
a 10-year period. Higher fiber choices include whole grains instead of refined, more fruits
and veggies, and whole fruits instead of fruit juice or (perish the thought) soft drinks.
How Do You Know What Your Set-point Is?
In an ideal world, it would be the weight you maintain without conscious effort. But we’re
not living in an ideal world, at least from the set-point perspective. (Remember the rats
and the tasty diet?) So the best way to determine your unique set-point is to think back to
when you were a child. Were you always “sturdy,” or were people on your case because they
thought a gust of wind would knock you over? That should give you an indication of the
natural weight your body will try to maintain. In other words, don’t aspire to be a size 4
if you were born to be a size 14.
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