Refueling: The Cycle of

Your body does its best to create cycles of activity that parallel a 24-hour day.
Like sleep, hunger occurs at pretty regular intervals, although your lifestyle
may make it difficult to follow this natural pattern — even when your stomach
loudly announces it’s empty!
Recognizing hunger
The clearest signals that your body wants food, right now, are the physical
reactions from your stomach and your blood that let you know it’s definitely
time to put more food in your mouth and — eat!
Growling and rumbling: Your stomach speaks
An empty belly has no manners. If you do not fill it right away, your stomach
will issue an audible — sometimes embarrassing — call for food. This rumbling
signal is called a hunger pang.
Hunger pangs actually are plain old muscle contractions. When your stomach’s
full, these contractions and their continual waves down the entire
length of the intestine — known as peristalsis — move food through your
digestive tract (see Chapter 2 for more about digestion). When your stomach’s
empty, the contractions just squeeze air, and that makes noise.
This phenomenon first was observed in 1912 by an American physiologist
named Walter B. Cannon. (Cannon? Rumble? Could I make this up?) Cannon
convinced a fellow researcher to swallow a small balloon attached to a thin tube
connected to a pressure-sensitive machine. Then Cannon inflated and deflated
the balloon to simulate the sensation of a full or empty stomach. Measuring the
pressure and frequency of his volunteer’s stomach contractions, Cannon discovered
that the contractions were strongest and occurred most frequently
when the balloon was deflated and the stomach empty. Cannon drew the obvious
conclusion: When your stomach is empty, you feel hungry.
Getting that empty feeling
Every time you eat, your pancreas secretes insulin, a hormone that enables you
to move blood sugar (glucose) out of the blood and into cells where it’s needed
for various chores. Glucose is the basic fuel your body uses for energy. (See
Chapter 8.) As a result, the level of glucose circulating in your blood rises and
then declines naturally, producing a vague feeling of emptiness, and perhaps
weakness, that prompts you to eat. Most people experience the natural rise
and fall of glucose as a relatively smooth pattern that lasts about four hours.