Test your nutrition knowledge by trying to figure out which food has the most of each nutrient.

Q. Which food has the most fiber?

A. Barley (1 cup)

B. Whole-wheat flour (1 cup)

C. Broccoli (1 cup)

D. Blueberries (1 cup)

A. Believe it or not, the barley has the most: 31.2 grams. Whole-wheat flour has 14.6 grams, broccoli 5.1 grams, and blueberries 3.5 grams.

Fiber is loaded with health benefits; it reduces your risk of heart disease and diabetes and lowers cholesterol. Plus, foods with fiber help to keep you fuller longer. Most people don't get enough fiber. Men should have 30-38 grams and women 21-25 grams per day.

Q. Which food has the most potassium?

A. Potato (1 medium)

B. Banana (1 large)

C. Raisins (1 cup)

D. Cucumber, with peel, raw (1 large)

A. One cup of raisins has 1,086 mg. The potato is a close second with 1,081 mg. Next is the banana with 537 mg, and, yes, even the cucumber is high in potassium with 442 mg.

Potassium is necessary for muscle contractions (including your heartbeat), transmission of nerve impulses, and the regulation of fluids and electrolytes. Diets rich in potassium blunt the adverse effects of salt on blood pressure, may reduce the risk of kidney stones and may decrease bone loss. The Institute of Medicine recommends 4,700 mg of potassium for adults, but more than 90 percent of Americans are not meeting this recommendation.

Q. Which food has the most iron?

A. Black beans, cooked (1 cup)

B. White mushrooms, boiled (1 cup)

C. Clams (3 ounces)

D. Prune juice (1 cup)

A. Clams offer the most iron with 23.77 mg in 3 ounces. Next are black beans with 3.61 mg, followed by prune juice with 3.02 mg, and mushrooms with 2.71 mg.

Iron is an essential component of hemoglobin, which carries oxygen in the blood, and myoglobin, which carries oxygen in muscle tissue. Many women are deficient in iron, resulting in fatigue, poor work performance and reduced immunity. Men should get 8 mg per day and women 18 mg.

Q. Which food has the most selenium?

A. Whole-wheat flour (1 cup)

B. Couscous, cooked (1 cup)

C. Halibut, cooked ( 1/4 fillet)

D. Brazil nuts (1 ounce)

A. Brazil nuts are the highest by far, with 543.5 micrograms. Next is whole-wheat flour with 84.8 micrograms, then halibut with 74.4, and couscous at 43.2.

Selenium is a trace mineral that helps certain enzymes function properly in the body. There are also studies that show a reduction in prostate cancer for those with high levels of selenium in their blood. However, a recent study reported in the Journal of Clinical Oncology suggests that if you already have prostate cancer, it may be bad to take selenium. The recommended daily value is 70 micrograms.

Charles Stuart Platkin is a nutrition and public-health advocate, and founder of www.DietDetective.com.