Two-thirds of all visits to the doctor include a written prescription. To get the most benefit from a drug, you might need to take it with food, on an empty stomach or while avoiding certain foods. How much do you know about food-and-drug interactions? Test yourself with this quiz.

CHRIS ROSENBLOOM FIT TO EAT Have a question of general interest? E-mail Rosenbloom Related: • More on food and drink • Restaurant reviews and search More Rosenbloom You can work '101 Foods' into your diet  Know your nutrition: A quick quiz for fall  Three to be careful with in healthy diet  Grapefruit, cancer link considered preliminary  Beta carotene powers orange fruits, veggies  Our levels of the 'sunshine' vitamin decrease as we age  'Repair' muscles after long-distance running  Food-drug interaction an important issue  • Chris Rosenbloom, Ph.D., R.D., is a member of the nutrition faculty in the College of Health and Human Sciences at Georgia State University.

1. Mevacor and Zocor are drugs that can lower your cholesterol. What food can interact with these drugs to cause increased absorption from the gut, meaning that more of the drug will be in your system than recommended?
a) peanuts
b) milk and dairy foods
c) grapefruit

Grapefruit (fresh, canned, frozen or juice) can increase the amount of drug that your body absorbs, sometimes tripling the level. Scientists aren't sure which of the many compounds in grapefruit causes this effect, but it is wise to switch to another citrus juice or fruit while taking these medications. Cholesterol-lowering drugs aren't the only ones that interact with grapefruit; several blood pressure drugs, anxiety drugs and drugs that suppress the immune system can also react with grapefruit. Read the insert that comes with your medication and ask your doctor or pharmacist if you should avoid grapefruit when taking a drug prescribed for you.

2. Iron deficiency anemia is often treated with ferrous sulfate (a type of prescription iron supplement). What foods or beverages should you take with the supplement to help improve its absorption, and what foods or beverages should you avoid because they hinder absorption?
a) milk and iced tea
b) coffee and chocolate
c) orange juice and milk
d) beef and carrots

The answer is (c); citrus foods and juice improve about threefold the absorption of iron. However, some foods, like milk, can bind iron, making it less available for absorption. So take iron supplements with orange juice, but not with milk.

3. To treat conditions like asthma and rheumatoid arthritis, drugs called corticosteroids are often prescribed because they can decrease pain and inflammation. Persons taking corticosteroids should also take supplements of:
a) vitamin A and iron
b) calcium and vitamin D
c) vitamin C and magnesium
d) B vitamins

Corticosteroids are potent drugs with potent side effects, and one of the most serious side effects is bone loss that can result in osteoporosis. It is recommended that those on long-term steroid use take 1,500 milligrams of calcium and 800 IU of vitamin D every day to protect their bones. Don't forget to add exercise; walking can help make strong bones, too.

4. Your doctor prescribed Coumadin to reduce the risk of blood clots. You should completely eliminate all foods with vitamin K when taking blood thinners.
a) true
b) false

It might come as a surprise, but the answer is (b). You don't need to completely eliminate all foods containing vitamin K, but you should limit your intake. My students would say that is a trick question, but it is more important to keep a constant, consistent intake of vitamin K than to eliminate it altogether. Foods that are highest in the vitamin should be limited to no more than one serving a day (cooked kale, cooked spinach, cooked turnip, collard and mustard greens and raw parsley), and those foods moderately high in vitamin K can be eaten in smaller amounts (1 cup), including raw spinach, leaf or romaine lettuce, broccoli and brussels sprouts.