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Nutrition
and the Liver:
The liver is the major organ responsible for regulating and responding
to your body's metabolic demands. Your liver must be functioning well to
maintain normal metabolism of carbohydrates, fats, and protein; it is
also responsible for processing and using several vitamins. This section
deals with the role and healthy liver (and a healthy, well-balanced
diet) plays in these nutritional processes.
Carbohydrate
Metabolism:
The most common sources of dietary carbohydrate are sugars, such as
sucrose (table sugar), fructose (corn syrup), and lactose (milk sugar),
and starches, such as breads, pasta, grains, cereals, fruits,
vegetables, and potatoes. When you eat carbohydrates, specialized
enzymes in the pancreas and gut process them to yield simple sugars
(glucose, galactose, fructose, maltose).
These
sugars are absorbed by intestinal lining cells, enter the portal
circulation, and travel to the liver via the portal vein. During
overnight fasting, blood sugar levels dip to a relatively low level,
insulin secretion is suppressed, and blood insulin levels diminish.
After a meal, blood sugar increases (stimulating the release of insulin
from the pancreas), and insulin levels rise. Insulin, which rises in
response to a meal, is the hormone that stimulates the liver to take in
more glucose and to move the glucose into storage -- mainly in the form
of glycogen. The liver can then release glycogen to your muscles for
energy during periods of fasting or exercise. Although the liver can
store considerable amounts of glycogen, it is the first energy source
used during periods of prolonged fasting or caloric deprivation, and it
can be depleted rapidly. After glycogen, the body taps other energy
sources -- including protein and fat.
Protein
Metabolism:
We take in dietary protein from dairy products, produce, and meats.
Enzymes produced by the pancreas and intestine break down the protein
into its amino acids and small peptides. The intestine rapidly absorbs
the amino acids with specific transport systems within its lining cells
and then delivers the amino acids to the liver via the portal vein. When
they reach the liver, they are used for energy or for making
(synthesizing) new proteins. The newly synthesized proteins perform
specific body functions.
Fat
Metabolism:
In general, fats are neutral lipids (triglycerides), acidic lipids
(fatty acids), and sterols (cholesterol, plant sterols). Triglycerides
(dairy products, meats, oils, butter, margarine) are the most common
type of dietary fat and represent a major source of energy. The liver is
uniquely suited to regulate and process triglycerides.
Dietary
triglyceride is digested in the intestine by lipase, an enzyme secreted
by the pancreas in response to meals. Bile, secreted by the liver, makes
the digested fat soluble and promotes its absorption. Absorbed fat is
then repackaged and transported into blood, where the liver ultimately
removes it from the circulation. Fat that reaches the liver is processed
in three ways: (1) stored as fat droplets in liver cells, (2)
metabolized as a source of energy, and (3) repackaged, secreted back
into blood, and delivered to other cells in the body.
The
liver is also intimately involved with the processing of dietary
cholesterol and is the main source of newly synthesized cholesterol in
the body. Liver disease may be associated with both high or low blood
cholesterol levels. In general, as liver disease progresses in patients
with hepatitis C, the blood level of cholesterol drops.
Bile:
The liver produces and secretes a fluid (bile) that enters the intestine
to aid in digestion and absorption. Bile is clear yellow to golden-brown
and contains water, electrolytes (salts), cholesterol, bile salts
(detergents), phospholipids, and proteins. Bile helps to activate
enzymes secreted by the pancreas and is essential for the digestion and
absorption of fat or fat-soluble vitamins.
Source:
"Living with Hepatitis C: A Survivor's Guide" by Gregory T.
Everson, M.D., and Hedy Weinberg. 1997, Hatherleigh Press.
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