Alcohol and
NutritionNutrition 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.
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. Alcohol impairs nutrient absorption by
damaging the cells lining the stomach and intestines and disabling transport of
some nutrients into the blood. 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.
Even if nutrients are digested and absorbed, alcohol can
prevent them from being fully utilized by altering their transport, storage,
and excretion. Decreased liver stores of vitamins such as vitamin A, and
increased excretion of nutrients such as fat, indicate impaired utilization of
nutrients by alcoholics.
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.
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). In
non-diabetic 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. 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. 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. 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.
The
mechanisms accounting for the apparent inefficiency in converting alcohol to
energy are complex and incompletely understood, but several mechanisms have
been proposed. For example, chronic drinking triggers an inefficient system of
alcohol metabolism, the microsomal ethanol-oxidizing system (MEOS). 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.
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. 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. Vitamin A deficiency can be
associated with night blindness, and vitamin D deficiency is associated with
softening of the bones.
Vitamins A, C, D, E, K, and the B vitamins,
also deficient in some alcoholics, are all involved in wound healing and cell
maintenance. 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. Rather,
deficiencies seem to occur secondary to other alcohol-related problems:
decreased calcium absorption due to fat mal-absorption; magnesium deficiency
due to decreased intake, increased urinary excretion, vomiting, and diarrhea;
iron deficiency related to gastrointestinal bleeding; and zinc mal-absorption
or losses related to other nutrient deficiencies. Mineral deficiencies
can cause a variety of medical consequences from calcium-related bone disease
to zinc-related night blindness and skin lesions.
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. 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.
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