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Understanding Macronutrients
Carbohydrates
Fats
Proteins
Carbohydrate digestion starts in the
mouth. Starch in foods mixes with your
saliva during chewing.
The enzyme called Salivary amylase
breaks starch into smaller particles,
eventually it will be disaccharide
maltose which are not digested in the
mouth.
Chewing activates secretion of saliva to
help form the bolus of food in the
mouth; then it moves down to the
stomach, where the digestion of
carbohydrates finishes.
In the Small Intestine, where the
majority of the carbohydrate digestion
occurs, the pancreas secretes an
enzyme called pancreatic amylase that
breaks down the remaining starch into
maltose.
Maltase, sucrase and lactase break
down disaccharides into
monosaccharides in the small intestine.
All monosaccharides are absorbed by
small intestine.
In the liver, monosaccharides are
converted into glucose and then
transported into cells as energy. Excess
glucose is stored as glycogen.
Fats are not soluble in water, therefore
most fat reaches the stomach intact
where it is mixed and broken into
droplets.
In the mouth only occurs a little lipid
digestion; however some triglycerides
are digested by an enzyme called
lingual lipase.
Gallbladder, Liver and Pancreas
contributes in fat digestion. As fat
comes into the small intestine from the
stomach, the gallbladder contracts and
releases a substance called Bile that is
produced in the liver from cholesterol
and is stored there until needed.
On the other hand, lipid digesting
enzymes produced in the pancreas
goes into the small intestine. Each
triglyceride molecule is broken down
into two free fatty acids and one
monoglyceride.
Absorption of fats occurs in the
mucosal lining of the small intestine.
Due to the fact that fats do not mix
with water are not easily of being
transported into the bloodstream.
Fatty acids are reformulated into
triglycerides and then packaged into
lipoproteins before being release into
the bloodstream. Excess fat is stored in
the adipose cell.
Proteins in food are crushed by
chewing and moistened by saliva.
There is no protein digestion in the
mouth.
When protein reaches the stomach,
hydrochloric acid converts pepsinogen
into its active form, pepsin which is
itself a protein that work optimally in
an acidic environment.
There is a hormone gastrin that
controls the production of hydrochloric
acid and the release of pepsin. Pepsin
begins breaking proteins into single
amino acids and shorter polypeptides;
both then travel to the small intestine
for further digestion and absorption.
When polypeptides reach the small
intestine, the pancreas and the small
intestine secrete enzymes that digest
them into oligopeptides, tripeptides,
dipeptides and single amino acids. The
enzymes that digest proteins in the
small intestine are called proteases.
Once in the liver, amino acids may be
converted to glucose or fat.
Amino acids are transported to the
liver and sent to the cells as needed.
These macronutrients study teach me that carbohydrates are not fattening. Sugars do not cause
hyperactivity in children. Some Fats are essential for good health. Carbohydrates and Fats are the
primary source of energy; Proteins are not the primary source of energy for my body. The majority of
the US population consume almost two times more protein than we need.