Drug-Nutrient Interactions:
What and When You Eat Matters
A drug-nutrient interaction is the specific changes that a nutrient may cause to the actions of a
drug, or the changes that a drug may cause to the actions of a nutrient.
Not paying attention to potential drug-nutrient interactions is risky. Ignoring these possible
interactions could lead to medications not achieving their intended effects, discontinuation of
medication usage because of adverse side effects, the need for additional medication, and disease
complications.
Normal drug absorption/metabolism
Drugs usually are absorbed mainly in the small intestine and then transported through the
intestinal lining to the blood. The drugs are then deposited into the fat or muscle, or are bound to
proteins and carried throughout the body. The liver inactivates the drug, and the kidneys excrete
it once it is metabolized.
Age
Many age-related changes impact the way that drugs are absorbed. For example, drugs are either
fat soluble or water soluble. The changes that occur with normal aging are an increase in body fat
and a decrease in body water, which obviously causes a difference in absorption of the drugs in
an older person vs a younger person. Another reason for age-related changes in the metabolism
of drugs is that the liver and kidneys, intricate to the inactivation and elimination of drugs,
become smaller with age and blood flow lessens, leading to an increased risk for medication to
build up in the system.
Disease and drug absorption/metabolism
A decrease in albumin, which often occurs with malnutrition, chronic heart failure, chronic renal
disease, rheumatoid arthritis, cirrhosis, and some cancers, can affect drug metabolism, and
because drugs often are carried by albumin, an albumin deficiency could lead to drug toxicity.
Diseases that change the rate of passage through the gastrointestinal (GI) tract, such as irritable
bowel syndrome, also affect the absorption of nutrients.
Drugs and nutrition
Vitamin and mineral deficiencies may develop in a person if the nutrients are bound to the drug
and excreted along with it. A good example of this is the many antacids that bind phosphate, so
that the phosphate is unusable. This results in hypophosphatemia, with the attendant symptoms
of weakness, fatigue, and osteomalacia. Furthermore, phosphate is necessary for the absorption
of riboflavin, copper, and iron, so these minerals also could end up in short supply.
Another example is antibiotics, which can kill the GI system’s natural flora (bacteria), which is
necessary for the absorption of thiamine, riboflavin, vitamin B6, vitamin B12, vitamin K, and
biotin. Iron also binds to some antibiotics, and absorption of iron is decreased. These are just two
examples of drug-nutrient binding that causes nutrient deficiencies.
Drugs that change the functioning of the GI tract will naturally affect the absorption of nutrients.
Damage to the lining of the GI tract, which normally contains enzymes necessary for food
digestion and supplies transporters to carry nutrients into the blood, can occur with certain drugs,
such as aspirin. Some drugs cause decreased usage of vitamins and/or minerals by changing the
acid content of the stomach, especially necessary for absorption of vitamin B12, and other
conditions necessary for proper absorption.
The speed of nutrients as they move through the GI tract may cause some deficiencies to
develop. For example, laxatives speed up the rate of elimination, moving fat-soluble vitamins
(vitamins A, D, E, and K) too quickly through the system for absorption. Laxative usage also can
cause serious electrolyte imbalances. Individuals using laxatives should do so only under the care
of a physician.
Drug side effects
Some drugs cause hyperphagia (increased hunger) or hypophagia (decreased hunger), which can
lead to body weight changes. Other drugs cause changes in taste (ie, imparting a metallic flavor
to any food eaten).
The following can occur with some medications and can alter a person’s nutritional well-being:
 Changes to smell
 Dry mouth
 Mouth pain
 Difficulty swallowing
 Nausea
 Vomiting
 Shaking
 Agitation
 Dizziness
 Sleepiness
 Light-headedness
 Confusion
 Unusual cravings
Impact of nutrition
Non-nutrient compounds in food can impact drug metabolism. For example, compounds in
cabbage, broccoli, and cauliflower can increase the rate of medication metabolism. Grapefruit
juice inhibits the intestinal enzyme that breaks down many medications and may lead to drug
toxicity, regardless of when the grapefruit juice is ingested. Some studies have demonstrated a
similar effect exerted by Seville oranges (often used in marmalade), pomelos, and tangelos.
Side effects associated with the use of hypnotics, antidepressants, and antianxiety drugs are
sometimes exaggerated by the consumption of alcohol. Alcohol also can have strong effects on
people taking a variety of other drugs, including beta-blockers and diabetes medications. Alcohol
use is not recommended when taking any medication that may lead to liver toxicity, such as
Tylenol®. Caffeine can interact with medications to increase the stimulant effects of caffeine,
often by reducing excretion of the caffeine.
You should not take some medications, particularly antibiotics, with foods containing calcium or
iron, because these nutrients decrease the absorption of these medications. Sometimes, the basic
components of a diet can alter drug metabolism. For example, the bronchodilator theophylline
requires a high-carbohydrate, low-protein diet for optimal use by the body. A high-fiber diet can
inhibit the absorption of digoxin and tricyclic antidepressants.
When to take drugs
It is important to take drugs at the recommended times. Sometimes drug absorption is reduced,
delayed, or increased by the presence of food. Most drugs are absorbed more quickly on an
empty stomach, which is sometimes good and sometimes not.
Some drugs need exposure to stomach acid for a longer period of time to break down properly.
Patients usually are advised to take these medications with food, which holds the medication in
the stomach and exposes it to acid for longer. Acidic foods or beverages are not recommended
when taking some medications, because the increase in stomach acid may interfere with drug
absorption.
If you are to take a medication on an empty stomach, you should avoid eating 1 hour before
taking the medication and 2 hours after taking it.
References and recommended readings
Pronsky ZM, Crowe JP. Food-drug interactions. In: Mahan LK, Escott-Stump S, Raymond JL.
Krause’s Food and the Nutrition Care Process. 13th ed. St Louis, MO: Elsevier Saunders;
2012:209-228.
Santos CA, Boullata JI. An approach to evaluating drug-nutrient interactions. Pharmacotherapy.
2005;25(12):1789-1800. http://www.medscape.com/viewarticle/518759_1. Accessed March 21,
2014.
Review Date 3/14
G-0865