nutritional deficiencies

Although the potential health hazards associated with food additives and contaminants are of concern, much more significant are the global health problems associated with inadequate nutrition. In third world countries, undernutrition or protein-energy malnutrition (PEM) continues to be common; in industrialized societies, the most frequent diseases (atherosclerosis, cancer, diabetes, and hypertension) have all been linked to some form of dietary impropriety.

An adequate diet should provide: (1) energy, in the form of carbohydrates, fats, and proteins; (2) essential (as well as nonessential) amino acids and fatty acids to be used as building blocks for synthesis of structural and functional proteins and lipids; and (3) vitamins and minerals, which function as coenzymes or hormones in vital metabolic pathways or, as in the case of calcium and phosphate, as important structural components.

In primary malnutrition, one or all of these components are missing from the diet. By contrast, in secondary or conditional malnutrition, the supply of nutrients is adequate, but malnutrition may result from nutrient malabsorption, impaired nutrient use or storage, excess nutrient losses, or increased need for nutrients.

In developing nations, the incidence of overt hunger is high, and the incidence of more subtle forms of undernutrition is even higher. Vitamin A deficiencies are rampant in certain parts of Africa, iodine deficiencies occur in regions where iodized salt is not available, and iron deficiency is often seen in infants fed exclusively milk diets. Thus, ignorance about the nutritional value of foods also plays an important role in malnutrition. In the United States, the National Research Council recommends daily allowances for protein, vitamins, and minerals for healthy adults, specifying ranges for both men and women. These standards represent the scientifically based general consensus of the safe (not minimal) amounts of each nutrient necessary to maintain good health. Debates continue as to optimal levels of fat and fiber to prevent cardiovascular disease and cancer, and this subject is briefly discussed later.

Affluent societies are not immune to a significant incidence of undernutrition. The following listing of common causes in the United States highlights this point:

 Ignorance and poverty. Homeless persons, aged individuals, and children of the poor demonstrate effects of PEM as well as trace nutrient deficiencies. Even the affluent may fail to recognize that infants, adolescents, and pregnant women have increased nutritional needs.

 Chronic alcoholism. Alcoholics may sometimes suffer PEM but are more frequently deficient in several vitamins, especially thiamine, pyridoxine, folate, and vitamin A, owing to a combination of dietary deficiency, defective gastrointestinal absorption, abnormal nutrient use and storage, increased metabolic needs, and an increased rate of loss. A failure to recognize the likelihood of thiamine deficiency in chronic alcoholics may result in irreversible brain damage (e.g., Korsakoff psychosis, discussed later).

 Acute and chronic illnesses. The basal metabolic rate becomes accelerated in many illnesses (in patients with extensive burns, it may double), resulting in an increased daily requirement for all nutrients. Failure to appreciate this fact can compromise recovery.

 Self-imposed dietary restriction. Anorexia nervosa, bulimia nervosa, and less overt eating disorders affect a large population of individuals who are concerned about body image or suffer from an unreasonable fear of cardiovascular disease.

Other, less common causes of malnutrition include the malabsorption syndromes, genetic diseases, specific drug therapies (which block uptake or use of particular nutrients), and total parenteral nutrition.

In the sections that follow, we barely skim the surface of nutritional disorders. Included in the discussion are PEM, deficiencies of most of the vitamins and trace minerals, obesity, and a brief overview of the relationships of diet to atherosclerosis and cancer.

Types

 protein-energy malnutrition
 anorexia
 vitamin deficiencies