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Nutrition is a process that serves two purposes: to provide energy and to
maintain body structure and function. Food supplies energy and provides the
building blocks needed to replace worn or damaged cells and the nutritional
components needed for body function. Alcoholics often eat poorly, limiting their
supply of essential nutrients and affecting both energy supply and structure
maintenance. Furthermore, alcohol interferes with the nutritional process by
affecting digestion, storage, utilization and excretion of nutrients
[1].
Impairment of Nutrient Digestion and Utilization
Once
ingested, food must be digested (broken down into small components) so it is
available for energy and maintenance of body structure and function. Digestion
begins in the mouth and continues in the stomach and intestines, with help from
the pancreas. The nutrients from digested food are absorbed from the intestines
into the blood and carried to the liver. The liver prepares nutrients either for
immediate use or for storage and future use.
Alcohol inhibits the
breakdown of nutrients into usable molecules by decreasing secretion of
digestive enzymes from the pancreas [2]. Alcohol impairs nutrient absorption by
damaging the cells lining the stomach and intestines and disabling transport of
some nutrients into the blood [3]. In addition, nutritional deficiencies
themselves may lead to further absorption problems. For example, folate
deficiency alters the cells lining the small intestine, which in turn impairs
absorption of water and nutrients including glucose, sodium and additional
folate [3].
Even if nutrients are digested and absorbed, alcohol can
prevent them from being fully utilized by altering their transport, storage and
excretion [4]. Decreased liver stores of vitamins such as vitamin A [5] and
increased excretion of nutrients such as fat, indicate impaired utilization of
nutrients by alcoholics [3].
Alcohol and Energy Supply
The
three basic nutritional components found in food — carbohydrates, proteins and
fats — are used as energy after being converted to simpler products. Some
alcoholics ingest as much as 50 percent of their total daily calories from
alcohol, often neglecting important foods [3,6].
Even when food intake is
adequate, alcohol can impair the mechanisms by which the body controls blood
glucose levels, resulting in either increased or decreased blood glucose
(glucose is the body's principal sugar) [7]. In nondiabetic alcoholics,
increased blood sugar, or hyperglycemia — caused by impaired insulin secretion —
is usually temporary and without consequence. Decreased blood sugar, or
hypoglycemia, can cause serious injury even if this condition is short-lived.
Hypoglycemia can occur when a fasting or malnourished person consumes alcohol.
When there is no food to supply energy, stored sugar is depleted and the
products of alcohol metabolism inhibit the formation of glucose from other
compounds such as amino acids [7]. As a result, alcohol causes the brain and
other body tissue to be deprived of glucose needed for energy and
function.
Although alcohol is an energy source, how the body processes
and uses the energy from alcohol is more complex than can be explained by a
simple calorie conversion value [8]. For example, alcohol provides an average of
20 percent of the calories in the diet of the upper third of drinking Americans,
and we might expect many drinkers who consume such amounts to be obese. Instead,
national data indicate that, despite higher caloric intake, drinkers are no more
obese than nondrinkers [9,10]. Also, when alcohol is substituted for
carbohydrates, calorie for calorie, subjects tend to lose weight, indicating
that they derive less energy from alcohol than from food [summarized in
8].
The mechanisms accounting for the apparent inefficiency in converting
alcohol to energy are complex and incompletely understood [11], but several
mechanisms have been proposed. For example, chronic drinking triggers an
inefficient system of alcohol metabolism, the microsomal ethanol-oxidizing
system (MEOS) [1]. Much of the energy from MEOS-driven alcohol metabolism is
lost as heat rather than used to supply the body with energy.
Alcohol
and the Maintenance of Cell Structure and
Function
Structure
Because cells are made mostly of
protein, an adequate protein diet is important for maintaining cell structure,
especially if cells are being damaged. Research indicates that alcohol affects
protein nutrition by causing impaired digestion of proteins to amino acids,
impaired processing of amino acids by the small intestine and liver, impaired
synthesis of proteins from amino acids, and impaired protein secretion by the
liver [3].
Function
Nutrients are essential for proper body
function; proteins, vitamins and minerals provide the tools that the body needs
to perform properly. Alcohol can disrupt body function by causing nutrient
deficiencies and by usurping the machinery needed to metabolize
nutrients.
Vitamins
Vitamins are essential to maintaining
growth and normal metabolism because they regulate many physiological processes.
Chronic heavy drinking is associated with deficiencies in many vitamins because
of decreased food ingestion and, in some cases, impaired absorption, metabolism
and utilization [1,12]. For example, alcohol inhibits fat absorption and thereby
impairs absorption of the vitamins A, E and D that are normally absorbed along
with dietary fats [12,13]. Vitamin A deficiency can be associated with night
blindness, and vitamin D deficiency is associated with softening of the bones
[6].
Vitamins A, C, D, E, K and the B vitamins, also deficient in some
alcoholics, are all involved in wound healing and cell maintenance [14]. In
particular, because vitamin K is necessary for blood clotting, deficiencies of
that vitamin can cause delayed clotting and result in excess bleeding.
Deficiencies of other vitamins involved in brain function can cause severe
neurological damage.
Minerals
Deficiencies of minerals such
as calcium, magnesium, iron and zinc are common in alcoholics, although alcohol
itself does not seem to affect the absorption of these minerals [15]. Rather,
deficiencies seem to occur secondary to other alcohol-related problems:
decreased calcium absorption due to fat malabsorption; magnesium deficiency due
to decreased intake, increased urinary excretion, vomiting and diarrhea [16];
iron deficiency related to gastrointestinal bleeding [3,15]; and zinc
malabsorption or losses related to other nutrient deficiencies [17]. Mineral
deficiencies can cause a variety of medical consequences from calcium-related
bone disease to zinc-related night blindness and skin
lesions.
Alcohol, Malnutrition and Medical
Complications
Liver Disease
Although alcoholic liver damage
is caused primarily by alcohol itself, poor nutrition may increase the risk of
alcohol-related liver damage. For example, nutrients normally found in the
liver, such as carotenoids, which are the major sources of vitamin A, and
vitamin E compounds are known to be affected by alcohol consumption [18,19].
Decreases in such nutrients may play some role in alcohol-related liver
damage.
Pancreatitis
Research suggests that malnutrition may
increase the risk of developing alcoholic pancreatitis [20,21], but some
research performed outside the United States links pancreatitis more closely
with overeating [21]. Preliminary research suggests that alcohol's damaging
effect on the pancreas may be exacerbated by a protein-deficient diet
[22].
Brain
Nutritional deficiencies can have severe and
permanent effects on brain function. Specifically, thiamine deficiencies, often
seen in alcoholics, can cause severe neurological problems such as impaired
movement and memory loss seen in Wernicke/Korsakoff syndrome
[23].
Pregnancy
Alcohol has direct toxic effects on fetal
development, causing alcohol-related birth defects, including fetal alcohol
syndrome. Alcohol itself is toxic to the fetus, but accompanying nutritional
deficiency can affect fetal development, perhaps compounding the risk of
developmental damage [24,25].
The nutritional needs during pregnancy are
10 percent to 30 percent greater than normal; food intake can increase by as
much as 140 percent to cover the needs of both mother and fetus [24]. Not only
can nutritional deficiencies of an alcoholic mother adversely affect the
nutrition of the fetus, but alcohol itself also can restrict nutrition flow to
the fetus [24,25].
Nutritional Status of
Alcoholics
Techniques for assessing nutritional status include taking
body measurements such as weight, height, mass and skin fold thickness to
estimate fat reserves, and performing blood analysis to provide measurements of
circulating proteins, vitamins and minerals. These techniques tend to be
imprecise, and for many nutrients, there is no clear "cut-off" point that would
allow an accurate definition of deficiency [4]. As such, assessing the
nutritional status of alcoholics is hindered by the limitations of the
techniques. Dietary status may provide inferential information about the risk of
developing nutritional deficiencies. Dietary status is assessed by taking
patients' dietary histories and evaluating the amount and types of food they are
eating.
A threshold dose above which alcohol begins to have detrimental
effects on nutrition is difficult to determine. In general, moderate drinkers
(two drinks or less per day) seem to be at little risk for nutritional
deficiencies. Various medical disorders begin to appear at greater
levels.
Research indicates that the majority of even the heaviest
drinkers have few detectable nutritional deficiencies but that many alcoholics
who are hospitalized for medical complications of alcoholism do experience
severe malnutrition [1,12]. Because alcoholics tend to eat poorly — often eating
less than the amounts of food necessary to provide sufficient carbohydrates,
protein, fat, vitamins A and C, the B vitamins, and minerals such as calcium and
iron [6,9,26] — a major concern is that alcohol's effects on the digestion of
food and utilization of nutrients may shift a mildly malnourished person toward
severe malnutrition.
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