What really happens to what you eat?

A man eating a cookie.

“I’m hungry!”

When your body makes this urgent demand, few put up much resistance to it.

But did you ever wonder what happens to what you eat?

But what happens in between and why it happens is for the most part a real mystery—even to scientists.

Let us, nevertheless, take a close look at current theories as to how the human machine is “fueled.”

Why you get hungry?

A lady having a snack at a restaurant.

The expression “you are what you eat”.

Your body cells are almost entirely composed of molecules extracted from foods and liquids you have consumed.

Constantly your body is fueling, making, repairing or destroying these cells.

So eating has a greater purpose than filling one’s stomach.

It provides fuel and material for your body’s nonstop construction program.

Our body is wisely designed with an alarm that lets us know when our bodies need more food.

Many researchers believe that a part of the brain called the hypothalamus—not the stomach—plays a large part in igniting the desire to eat.

True, a person with an empty stomach can suffer what maybe called “the pangs of hunger”—sharp stomach contractions.

But most of us have never experienced this.

Often one’s eating is prompted by habit or by psychological factors.

Why, just the sight or smell of food can initiate hunger!

In addition, though, the brain seems to monitor the body’s level of glucose in the blood, and a drop in this level can make you feel hungry.

Some even think that the brain has a predetermined “set-point” controlling how much body fat you have.

Chemical “messengers” may inform the brain when fat levels are too low for the brain’s liking. As a result, you feel hungry.

Fortunately, the brain also informs you when you have eaten enough.

But if this system malfunctions (as it seems to do in some people), one may eat long past the point of satiation.

This may be one of the many causes of obesity.

The journey from mouth to stomach

Picture of digestive system.

Meat and vegetables supply vital nutrients, such as proteins, fats and starches. 

The problem is, however, that your body only assimilates small food molecules, whereas protein, fat and starch molecules are quite large. 

Digestion, therefore, chops these long chemical chains down to size.

From the moment you see, smell or even think about a tasty food item, your body prepares itself for digestion.

Imagine, for example, that you have before your eyes a piece of juicy, boneless breast of chicken, nestled between two fresh slices of whole-wheat bread.

Just the sight of it starts your mouth watering, doesn’t it?

Secretly, your stomach starts secreting digestive fluids.

Now take a healthy bite of this luscious treat and your body’s digestive system swings into full gear.

Your mouth warms (or cools) the food to the right temperature.

Chewing not only lets you savor the food but also grinds it to an easily swallowed pulp.

Salivary glands help by pumping out saliva to moisten and soften the food.

Enzymes in the saliva go to work on the bread, transforming starches into simple sugars.

From the mouth, your meal must now journey to its next stop—the stomach.

There the chicken can be digested.

Take a swallow. 

A reflex action closes your windpipe so that the food slides into the gullet, or esophagus.

Its stay there is quite brief, however.

Within a few seconds, muscle contractions help move it down toward the stomach.

“The contractions are so strong,” says one writer, “that food would be forced down even if the eater were standing on his or her head.”

A one-way valve called the cardiac, or lower esophagal, sphincter allows the food to pass into the stomach but prevents gastric juices from flowing back into the esophagus.

Anyone who has ever had the unpleasant experience of vomiting knows that the stomach is nothing less than a vat of acid.

So for several hours the food churns in hydrochloric acid and enzymes.

There your chicken is blended, sterilized and broken down into protein molecules called polypeptides.

Unfortunately, some people have a deficiency of hydrochloric acid and stomach enzymes.

As a consequence, their digestion is seriously impaired.

They may stuff themselves on nutritious food but suffer malnutrition nonetheless.

On the other hand, some have an excess of stomach acids and suffer the familiar heartburn or even develop ulcers.

A person does well to watch his diet and not eat foods that generally cause him stomach upset.

Be aware, too, of the effect of your emotions.

Absorption and distribution

Picture of an anatomy of a stomach.

Several hours in the stomach and the food is now a liquid mass called chyme.

This liquid is gradually squirted into the duodenum, the first part of the small intestine.

There the digestive process continues.

The liver then comes to the aid of enzymes present in the intestine by producing bile—a yellowish alkaline fluid.

Your body produces about 17 to 27 fluidounces (500 to 800 ml) of this salty fluid daily and stores it in the gallbladder.

When needed, this organ secretes just enough bile to do its job of emulsifying fatty globules.

This job accomplished, the enzymes are free to perform their chemical wonders.

What’s left of your sandwich is transformed into microscopic particles!

But how do these particles become a part of your body?

By absorption.

You see, it takes the digested food some four hours to pass from the small intestine to the next step of its journey: the large intestine. 

In the meantime, it encounters millions of tiny, finger-like projections called villi that line the walls of the small intestine. 

Through these villi, food is absorbed—either into the lymph (lymphatic) system or into the blood system.

The blood system carries away the digested food material to that remarkable “factory,” the liver.

There molecules are broken down yet further.

Now when your body cells need repair, the liver uses these raw materials to manufacture or synthesize “spare parts”—amino acids and proteins.

Too, it can store and later send out glucose to fuel your cells.

The liver is also a warehouse.

When further cell repair is needed, the body sends out a signal and the liver supplies some of the needed repair materials on demand.

What, though, of the food that wasn’t absorbed?

Water eventually goes to the kidneys for elimination via the urinary bladder.

Solid waste passes into the large intestine, or colon, for elimination through the rectum.

Since the colon is at its most efficient when it is relatively full (and there is evidence of further health benefits), many doctors recommend a diet high in fiber, that is, indigestible materials such as bran, to aid in regular elimination.

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