> Digestion & Nutrition
Digestion, Absorption & Elimination
Digestion is the process by which our bodies break down the food
and liquid into small molecules that our blood can absorb. Absorption
is the basis of nutrition: it is how our bodies pull into the bloodstream
the required nutrients from the food and liquid we digest in order
to provide energy and life to all of our cells. Elimination is the
process whereby our bodies excrete that which is not absorbed or
not useful; for example undigested food particles, toxins, and dead
cells. Our bodies have built in elimination systems that encompass
a range of activities from bowel movements and urination to sweating
and breathing. In other words, our bodies turn food and drink into
absorbable nutrients via our digestive system. When you eat an apple,
your body is performing many different tasks in order to turn that
apple into substances that it can use, and then efficiently eliminate
what is not useable. It is essential to our health to keep our digestive
and elimination systems functioning properly. Anything preventing
proper digestion, absorption and elimination directly affects our
bodies' ability to nourish our cells; when any part of this system
is not performing, the system cannot absorb all the nutrients from
the food being ingested and our bodies suffer.
The Digestive System - How it all comes together
The digestive system is composed of the organs of the alimentary
canal (also called the digestive tract), and the pancreas, liver,
and gallbladder. In addition, the nervous system and circulatory
system play a major role in assisting the digestive process. The
alimentary canal is the long hollow tube (about 30 feet long) that
starts with your mouth and ends with your anus. This tube includes
the mouth, the esophagus, the stomach, the small intestine (20 feet
long, three main parts: duodenum, jejunum and ileum), the large
intestine (5 feet long, six main parts: cecum, ascending colon,
transverse colon, descending colon, sigmoid colon, and rectum),
and the anus. Inside this tube is a lining called the mucosa. In
the mouth, stomach, and small intestine, the mucosa contains tiny
glands that produce juices to help digest food. For hours after
eating, these organs work together to push food through the body
while secreting juices that break the food into tiny nutrients that
can be absorbed. Protein gets broken down into amino acids, starches
into simple sugars, and fats into fatty acids and glycerol. Water
is absorbed into the bloodstream to hydrate the body.
How food is turned into nutrients - from start to finish
Before food even enters the mouth the body secretes saliva (enzymes)
to help moisten food and start the digestion of the starch in food
into smaller molecules.
Food is chewed up and pushed down the esophagus in a small lump
called a bolus. This lump of food is pushed down into the stomach,
where three things happen: the lumps of food are stored (up to a
half gallon can be stored), then mechanically blended with stomach
acids and an enzyme that digests protein (pepsin), and then emptied
as a liquid solution in spurts into the small intestine.
Things really get interesting as food is emptied from the stomach
to the small intestine, where the majority of digestion happens.
The pancreas secretes a variety of enzymes in a solution known as
pancreatic juice. This helps digest proteins, fats and carbohydrates,
and helps to neutralize the acids used to digest foods in the stomach.
The liver and gall bladder secret a substance called bile which
helps the body break apart and absorb fat. Bile is composed of bile
salts (produced by the liver's breakdown of cholesterol), cholesterol,
phospholipids, bilirubin (the yellow by-product of dead red blood
cells, which bacteria in the intestines modify, thereby causing
the brown color of feces), protein and miscellaneous components.
The bile is stored between meals in the gallbladder. When food
enters the small intestine, bile is squeezed out of the gallbladder
into the bile ducts and then into the small intestine. Bile dissolves
fat the same way detergents dissolve grease from a frying pan. After
the fat is dissolved, it can be digested. Bile and pancreatic juices
break down the food into tiny particles that can be absorbed across
the wall of the small intestines into the blood stream.
The wall of the small intestines has a huge surface area (around
1,600 square feet), due to presence of villi, which are fingerlike
projections in the lining of the small intestine (think of egg carton
foam mattress pads, and their expanded surface area.)
At the bases of the villi are openings of intestinal glands, which
secrete a watery intestinal juice containing digestive enzymes.
On average, about 2 quarts of intestinal juice are secreted into
the small intestine each day. As with the lining of the stomach,
a coating of mucus helps protect the lining of the small intestine.
The digestive enzymes wear away the lining, which is replaced about
every two days. These dead cells of the lining are pushed down the
digestive tract to be eliminated with other fecal matter.
Each villi contains a lymph vessel surrounded by a network of capillaries.
The nutrients absorbed into the lymph vessel pass into the lymphatic
system. The particles that are absorbed into the capillaries empty
into the portal vein and travel directly to the liver, where the
liver filters the blood of toxins and sends the filtered, nutrient-rich
blood to the heart for circulation around the body.
Simple sugars and amino acids pass through the capillaries to enter
the bloodstream. Fatty acids and glycerol pass through to the lymphatic
It is important to note that the small intestine, contains an extensive
immune system. The immune system protects the intestine from disease-causing
viruses, bacteria, yeasts, fungi and parasites. Beneficial bacteria
provide a defence against harmful organisms by taking up residence
where harmful bacteria would otherwise settle in. Additional beneficial
bacteria ("intestinal flora") live in the large intestine (we'll
cover this later.)
Unabsorbed and undigested food, along with water, digestive juices
and dead cells continue their journey through the small intestine
where some of the substances are reabsorbed and recycled (like bile
Whatever is not absorbed in the small intestine gets pushed
through to the large intestine.
By the time food gets to the large intestine, digestion is largely
completed. The primary goals now are the re-uptake of water, sodium
and minerals; the absorption of Vitamin K and B created as by-products
of bacteria that live in the large intestine; decomposition of undigested
food (aided by bacteria); and the compaction and elimination of
The large intestine hosts at least 500 different types of bacteria.
In fact, about 3-4 pounds of bacteria live in the large intestine.
These bacteria produce methane (CH4), hydrogen sulfide (H2S), and
other gases as they ferment their food.
Occasionally, some of this gas is released as flatus. As these
bacteria digest/ferment left-over food, they secrete beneficial
chemicals such as vitamin K, biotin (a B vitamin), and some amino
acids, and are our main source of some of these nutrients. Beneficial,
or symbiotic "friendly" bacteria have several roles in our bodies:
to protect us from bad bacteria; to assist with decomposition and
breakdown of undigested food; to synthesize vitamins B & K; to maintain
proper pH; and assist with immune system functions. Ideally, about
85% of the bacteria in your digestive tract are beneficial, and
have established large, healthy populations that keep the growth
of bad bacterial in check.
However, higher amounts of bad bacteria are usually present due
to a variety of reasons including poor/acidic diet, chlorinated
water, and antibiotics. Over-colonization of disease causing micro-organisms
like E. coli, Staphylococcus aureus, salmonella and Candida can
harm the body by producing toxins and even carcinogens.
Higher levels of bad bacteria also account for the production of
gases inside our intestine, which causes digestive discomfort, foul
flatulence and may be implicated in some diseases. In the large
intestine (a.k.a., the colon) water is absorbed back into the body
via the walls of the large intestine.
Approximately 1.6 quarts of water per day flows through the large
intestine, 85% of which comes from digestive secretions. 95% of
this water is reabsorbed into the intestinal walls. But if the water
is not absorbed, diarrhea can result.
The remains - rotting food, bacteria, dead epithelial cells from
the walls of the intestines, dead red blood cells filtered by the
liver and released in bile, and other toxins that were filtered
by the liver and secreted with bile during digestion - proceed to
the rectum, where they are stored until they are excreted as feces.
The evacuation of feces should occur at least daily, ideally two
or three times daily shortly after each meal. Constipation is defined
as having less than three bowel movements per week. Bowel movements
should be comfortable and easy. If you are forcing them, or if you
are not having a bowel movement for 1-2 days at a time (or for some
people even longer!) then your digestive system is not working
efficiently and you are likely over-exposed to rotting putrefying
food in your digestive tract.