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NUTRIENTS

bloodstream—neither too little nor too much. Therefore, switching from one formulation to another has to be done carefully.

Effects of Foods and Food Components on Drug Biotransformation

Biotransformation can be divided into two phases: Phase I, in which compounds are transformed by enzymes (pro- teins that transform the structure of other molecules such as drugs to make them either inactive or more active), and Phase II, in which compounds are prepared for ex- cretion in the urine by attaching a molecule that makes them soluble in water. The small intestine has some ca- pacity for drug biotransformation, but the major site of biotransformation is the liver. Because blood from the small intestine must pass through the liver before it goes on to the rest of the body, some drugs that are readily absorbed may not be bioavailable, because they are inac- tivated by the liver before they can get to the site of ac- tion. Blood flow through the liver, and the size of the liver itself, decrease as people age, so some drugs may be effective at lower doses in the elderly than in the young.

The dietary factors that activate the liver enzymes are just beginning to be elucidated. These include both nutritive factors (protein, carbohydrate, and fat) and non- nutritive factors, compounds in charbroiled meat, in cru- ciferous vegetables such as cabbage, turnip, and broccoli, and in citrus fruits, especially grapefruit. If you are tak- ing a drug that is activated or inactivated by liver en- zymes, it is important to maintain a diet that does not vary much from day to day in order to assure a steady level of the active drug in your bloodstream. Note that large changes in macronutrient composition of your diet, for example, adoption of a low-protein diet, can also af- fect Phase II biotransformation, and therefore drug ex- cretion.

Effects of Drugs on Food and Nutrient Intake and Function

Drugs can affect food and nutrient intake, either as a de- sired effect or as a side effect. They can alter appetite; cause nausea and vomiting; cause food aversions; alter the taste of food, decrease taste sensations, or cause the mouth to be painful; cause gastric irritation; and alter in- testinal function. One class of drugs that can cause all of these problems consists of the anticancer drugs, which can potentially cause malnutrition because they can de- crease food intake dramatically.

Specific Diet/Food-Drug Interactions

There is a large number of well-known food-drug inter- actions in which the drug’s action is altered by specific dietary components. Common examples are diuretics used for hypertension, digoxin used for cardiovascular disease, coumarin anticoagulants used for blood thinning, and monoamine oxidase (MAO) inhibitors used for de- pression. Similarly, there are a number of drugs, such as

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the drugs designed to reduce stomach acidity, that affect vitamin and mineral status, requirements, and activity.

Drugs can inhibit enzymes that may be critical for the metabolism of toxic substances in food. In the case of disulfiram, a drug used to curb alcohol consumption, the enzyme inhibition is the desired therapeutic effect. This drug inhibits aldehyde dehydrogenase, the enzyme that breaks down the aldehyde derived from alcohol con- sumption. As a result, people taking the drug become ill when they drink alcohol, and thus learn to avoid alcohol. For most drugs, however, food-drug incompatibility is an undesirable side effect.

General Principles

The considerations we have discussed bring us to enun- ciate two important general principles:

1. First, if you are taking any drug, either prescription or over-the-counter, be sure to consult your phar- macist concerning any nutrient-drug interaction for that drug.

2. Second, be sure to take both drug and food on a reg- ular basis, so that drug absorption, action, metabo- lism, and excretion are consistent and predictable.

See also Assessment of Nutritional Status; Disease: Meta- bolic Diseases; Enteral and Parenteral Nutrition; Health and Disease; Immune System Regulation and Nutrients; Intestinal Flora; Nutrients; Nutrition.

BIBLIOGRAPHY

Joint Commission on Accreditation of Healthcare Organiza-

tions. 1996 Comprehensive Accreditation for Hospitals. Regu-

lation PF2.2.3. Oakbrook Terrace, Ill., 1995.

Utermohlen, V. “Diet, Nutrition, and Drug Interactions.” In

Modern Nutrition in Health and Disease, edited by M. E.

Shils, J. A. Olson, M. Shike, and C. A. Ross, pp. 1619– 1641. 9th ed. Baltimore: Williams and Wilkins, 1999.

Virginia Utermohlen

NUTRIENTS. Nutrients are those organic and in- organic compounds that a living organism must acquire from the environment to support essential life processes, including basal metabolism, growth and maintenance of body tissues, activity, reproduction, and maintenance of general health. Nutrients are normally obtained by the ingestion of foods. Organic nutrients include carbohy- drates, proteins or amino acids, lipids, and vitamins. In- organic nutrients include minerals. Water is sometimes included in a listing of nutrients.

Classification of Nutrients

Nutrients often are classified as essential or nonessential. Essential nutrients are those that cannot be synthesized in the body at all or in sufficient amounts to meet needs and, thus, must be obtained preformed in the diet. These include the essential (indispensable) amino acids, the es-

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