TABLE 2.

Potential mechanisms to explain drug-nutrient interactions¹

Mechanism	Description
Ingestion	Both drugs and disease can cause changes in appetite and nutrient intake; resultant malnutrition can affect drug efficacy.
Absorption	Drugs and foods can have a mechanical effect, via binding or adsorption, that can increase or decrease drug and nutrient absorption. Some drugs can increase or decrease gastrointestinal motility, which may result in increased or decreased nutrient absorption. Chemical factors, in particular the pH of the stomach contents and the influence of foods therein, can affect the subsequent absorption of drugs. Nutritional status, infection, and inflammation can cause homeostatic responses, which lead to increased or decreased nutrient absorption.
Gastrointestinal transport	The ability of drugs and nutrients to be transported can depend on factors such as lipid solubility and competition for amino acid transport systems.
Metabolism	MFO and conjugase systems that convert drugs and nutrients into their active and excretory forms are nutrient/cofactor dependent. Certain drugs can increase the activity of the MFO systems required to convert nutrient precursors into their active forms. Nonnutritive components in foods/supplements can induce MFO activity and thereby affect drug metabolism.
Distribution	The use of both drugs and nutrients depends on body composition, the availability and functional integrity of transport proteins, receptor integrity, and intracellular metabolic machinery, all of which are sensitive to nutritional status and the impact of disease (inflammation and infection via the acute-phase response).
Elimination	Drugs and nutrients can synergistically and competitively interact to cause increased or decreased excretion. Systemic factors such as pH and physiologic state (eg, sweating) can dictate whether a drug or nutrient is excreted or resorbed.
Direct Action	The effectiveness of some drugs is directly related to their impact on nutrient metabolism (eg, antimalarial antifolate drugs, isoniazid, and vitamin B-6).

¹MFO, mixed-function oxygenase.