The immune system protects the body against infection by producing
specific substances in response to foreign materials called antigens.
Immunity to specific antigens occurs through the cooperative
interactions of two subsets of blood cells, T lymphocytes and B
lymphocytes.
There are several subtypes of T lymphocytes, each with specific
functions. Helper and suppressor T lymphocytes regulate the quantities
of antibodies produced, while killer T lymphocytes respond selectively
to foreign material, search and destroy internally infected, or
malignant body cells.
Severe infections can compromise nutritional status through a
variety of mechanisms: hypermetabolism, appetite depression, decreased
absorption of nutrients, altered nutrient metabolism, increased
nutrient excretion, and internal diversion of nutrients. additional
nutrient losses occur with vomiting, diarrhea, and sweating.
Hypermetabolism
Fever causes metabolic rates to increase. This hypermetabolism
affects all cells in the body. Because this extra energy comes largely
from amino acid metabolism the body stores of muscle protein amino
acids are rapidly depleted. Loss of nutrients also occur during
sweating associated with fever. Controlling the infection reduces fever
and losses of body nutrients.
Severe loss of appetite is a common symptom during most infectious
diseases and often leads to an almost total cessation of food
consumption. Vomiting and diarrhea further reduce the absorption of
nutrients. Antibiotics and other medications also modify intestinal
absorption.
Excess nitrogen is metabolized to urea and excreted in the urine.
Even brief viral infections and brief fevers induced by bacterial
infections can cause sizable losses of nitrogen.
Tissue and plasma concentrations of most vitamins decline during
infections, because of increased metabolism or excretion. The
accelerated metabolism or loss of vitamins during infections may
precipitate recognizable deficiency states.
Food Associated Illnesses
Adverse reactions to food involve immunologic and nonimmunologic
mechanisms. Immunologic reactions are known as food allergies.
Nonimmunologic intolerances include those that are biochemical or
psychologic.
Food allergies are examples of the negative consequences of immune
function on the gastrointestinal tract, skin, lungs, and other organs.
The most common foods to which people are allergic are eggs, milk,
fish, shellfish, chicken, wheat, and nuts. Symptoms include acute
abdominal pain, swelling, nausea,vomiting, rashes, chronic itching,
headache, tension, and fatigue.
The causes of nonimmunologic adverse reactions to foods include food
toxicities, food poisonings, and pharmacologic or metabolic reactions.
Such intolerances occur more frequently than true food allergies and
are related to dose as well as to the concurrent presence of
medications, other diseases, or genetic errors of metabolism.
Sulfites
Approximately 10 percent of people with asthma are sensitive to
ingestion of sulphite, which induces asthma. Foods containing sulfur
dioxide, as a preservative, should be used with caution.
FDA has taken two major steps to protect consumers who are sensitive
to sulfites in food. No longer can these preservatives be used on raw
fruits and vegetables. And processed foods that contain sulfites will
have to say so on the package label.
The allergic-type reactions range from mild to severe, and in some
cases can cause death. "Sulfites" or "sulfating agents" are general
terms used to describe sulfur based substances that have been in
widespread use for many years by the food and drug industries. They
include sulfur dioxide, sodium sulfite, sodium and potassium bisulfite,
and sodium and potassium metabisulfite. Although they have various
permitted uses, their primary function is as a preservative or
antioxidant to prevent or reduce spoilage and discolouration during the
preparation, storage and distribution of many foods.
There is some evidence that some non-asthmatics also can suffer
adverse reactions to sulfites. For example, out of more than 500
reports of sulfite reactions investigated by the FDA, about one-fourth
involved people who had no known history of asthma.
Asthma is also induced by tartrazine, a yellow dye used to color
medicines, soft drinks, and foods. Tartrazine can also cause
hyperactivity in sensitive individuals. It has no nutritional value.
Because of the negative effects associated with tartrazine, foods and
drinks containing it should be avoided. Other substances that cause
adverse reaction or neurologic disorders are monosodium glutamate (MSG)
and the preservative benzoic acid.
Psychologic mechanisms can provoke physical and mental symptoms of
food sensitivity that do not appear to be medicated by the immune
system. In individuals with psychologically induced allergic symptoms
no physiologic or biochemical nonimmunologic mechanisms can be
identified.
Individuals with food intolerances should exclude the offending
foods from their diet. Those with potentially life-threatening
sensitivities should carry an epinephrine-containing syringe and wear a
bracelet identifying the problem.
HIV Infection and AIDS
Acquired immunodeficiency syndrome (AIDS), caused by the human
immunodeficiency virus (HIV), is a disease with multiple pathologies,
most of which are the consequence of a profound immunodeficiency.
Weight loss and deteriorating nutritional status are critical
features of the AIDS disease. Anorexia, nausea and vomiting, fever, and
diarrhea are common features of advanced AIDS, as are malabsorption of
fats, carbohydrates, and protein. Immune abnormalities resulting from
malnutrition seen in AIDS implies that malnutrition might predispose to
AIDS or that nutritional therapy might improve immune status and
prevent AIDS.
Folate levels were measured in HIV-infected patients. For persons
not supplemented with folic or folinic acid and not taking antifolate
drugs, serum and erythrocyte folate was decreased significantly. Folate
deficiency was frequent and observed at all stages of HIV infection. [Boudes, P. et al: The Lancet. 335:1401, 1990.]
Nutrition Programs and Services
Food Labels:Evidence related to diet-immune function
interactions reinforces the need for food manufacturers to include
explicit and complete ingredient statements to protect individuals who
may have severe adverse reactions to foods.
Food Services:Current evidence about the role of dietary
factors in the maintenance of optimal immune function currently has no
special implications for change in policy related to food service
programs. Evidence related to the spread of infections suggests that
food service personnel should receive adequate training in sanitary
food handling and storage procedures.
Food Products:Evidence related to diet-immune function
interactions suggests that food product manufacturers should take
special precautions to use good manufacturing practices to avoid
contamination with ingredients that may produce severe reactions and to
reduce microbial and chemical contamination during production and
storage. Manufacturers should continue to develop new products that are
free of substances likely to induce allergic symptoms in susceptible
individuals. [The Surgeon General's Report on Nutrition & Health, 1988.]
