Nutrition can affect the body’s response to drugs; conversely, drugs can affect the body’s nutrition.
Foods can enhance, delay, or decrease drug absorption. Foods impair absorption of many antibiotics. They can alter metabolism of drugs; eg, high-protein diets can accelerate metabolism of certain drugs by stimulating cytochrome P-450. Eating grapefruit can inhibit cytochrome P-450 34A, slowing metabolism of some drugs (eg, amiodarone, carbamazepine, cyclosporine, certain calcium channel blockers, statins). Diets that alter the bacterial flora may markedly affect the overall metabolism of certain drugs.
Some foods affect the body’s response to drugs. For example, tyramine, a component of cheese and a potent vasoconstrictor, can cause hypertensive crisis in some patients who take monoamine oxidase inhibitors and eat cheese.
Nutritional deficiencies can affect drug absorption and metabolism. Severe energy and protein deficiencies reduce tissue enzyme concentrations and may impair the response to drugs by reducing absorption or protein binding and causing liver dysfunction. Changes in the gastrointestinal tract can impair absorption and affect the response to a drug. Deficiency of calcium, magnesium, or zinc may impair drug metabolism. Vitamin C deficiency decreases activity of drug-metabolizing enzymes, especially in older people.
Many drugs affect appetite, food absorption, and tissue metabolism (see table Effects of Some Drugs). Some drugs (eg, metoclopramide) increase gastrointestinal motility, decreasing food absorption. Other drugs (eg, opioids, anticholinergics) decrease gastrointestinal motility. Some drugs are better tolerated if taken with food.
Certain drugs affect mineral metabolism (see table Possible Effects of Drugs on Mineral Metabolism). Certain antibiotics (eg, tetracyclines) reduce iron absorption, as can certain foods (eg, vegetables, tea, bran).
Certain drugs affect vitamin absorption or metabolism (see table Possible Effects of Drugs on Vitamin Absorption or Metabolism).