DEAR DR. BLONZ: It would seem that olive oil is generally recognized by nutritionists as the best oil for cooking and baking. It is my understanding that there are three pressings of olives to make three grades of olive oil. Other than price, what is the difference between extra virgin, virgin and regular olive oil? -- D.D., Santa Barbara, California
DEAR D.D.: The main differences between the different grades of oilve oil are color, flavor, price and phytochemical content. Extra-virgin olive oil is the darkest, the most flavorful, the richest source of beneficial phytochemicals and the most expensive. Regular is the palest in color, has a minimum of the olive's fruitiness and phytochemicals, and is the least expensive. Virgin olive oil is midway in all these categories. All three are more or less identical in fat content: They are 100 percent fat, with the fatty acids being approximately 14 percent saturated, 77 percent monounsaturated and 9 percent polyunsaturated.
DEAR DR. BLONZ: My dad had colon cancer, and luckily it was caught in time. This puts me at higher risk. In addition to regular screenings, one of the things I am doing is staying away from foods that use nitrite preservatives, because they can form cancer-causing nitrosamines. I now read that spinach, beets and other vegetables I eat contain nitrates, and that these can convert to nitrites. How dangerous are the nitrates in foods, and are these things I should also be seeking to limit? -- F.S. Eureka, California
DEAR F.S.: While they are very closely related, there is an important difference between nitrates and nitrites. Nitrates are compounds that are naturally present in many different types of foods, including vegetables and fruits. Nitrites are food additives used in cured meat products to decrease the risk of botulism. Nitrosamines are carcinogenic compounds that form when a nitrite combines with an amine. (Amines are released when the amino-acid building blocks of protein are metabolized.)
Before a nitrate can become a nitrosamine, it must first be reduced (a chemical process) into a nitrite, and it then has to be alongside an amine in an environment that encourages their combination.
The conversion of nitrate to nitrite is usually handled by bacteria, and while there are bacteria in our saliva, they convert only a small amount of the nitrates we consume. The process is inhibited in an acid environment, so if there is vitamin C present, as is often the case with fruits and vegetables, it proceeds even more slowly. Nitrates tend to be absorbed after they leave the stomach. There are bacteria in the large intestine, but by that point there is a negligible risk of any nitrate stragglers finding and sidling up to an amine and turning into a nitrosamine.
Contrast all this with nitrite-preserved meat products, in which all the players (the nitrite and the amine from the meat protein) are there in the same package. There is no guarantee that nitrosamines will form -- and nitrites are certainly preferable to the risk of botulism -- but by comparison, the natural nitrates in fruits and vegetables represent a healthful walk in the park.
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