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.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Please forgive the indelicacy of this question, but is there something in asparagus that makes urine smell? My husband and I love asparagus, and now that it's spring, it is plentiful in our local market. We eat it every now and then, and I always seem to notice a telltale odor the next time I visit the bathroom. I only notice it after asparagus. My husband doesn't experience this. -- G.A. Sacramento, California

DEAR G.A.: Asparagus, garlic and onion are members of the lily family. These healthful vegetables all have sulfur-containing compounds that can give rise to distinctive odors. In the case of asparagus, though, the peculiar odor isn't noticeable in the raw vegetable. Rather, it comes from metabolic byproducts that are produced and then pulled out of the bloodstream by the kidneys soon after asparagus has been eaten.

There are some variables at play here: One is whether an individual produces the substances, and another is whether an individual is able to detect the odor. Most, but not all of us, produce varying concentrations of the byproducts. Some individuals are nonsmellers, while others are smellers but they can only detect the substances at certain concentrations. A capsule review of some of the science can be found at tinyurl.com/majcajz.

DEAR DR. BLONZ: When I hear about recalls of peanuts and other nuts (and nut butters) because of salmonella, I am puzzled. I had only thought this was an issue with raw nuts, not cooked ones. I was hoping you could explain. -- D.I., via email

DEAR D.I.: Nuts, whether they are peanuts, walnuts, almonds, pistachios, cashews or others, are great players in a healthful diet. In addition to providing healthful fats, they contain fiber and beneficial phytochemicals. No wonder that observational studies report that nut consumption is inversely associated with the incidence of cardiovascular disease and cancer.

Regarding peanuts, if we assume that roasting is done correctly, any salmonella contamination of a peanut should be completely eliminated during the roasting process, whether it's an oil roast or a dry roast. Oil roasting and dry (oven) roasting take place at temperatures well above the temperature needed to destroy this organism. It has to be done right, though, to assure that all the nuts get up to the right temperature. (An explanation of the temperatures used in peanut processing can be found at tinyurl.com/b6z7xa.)

Assuming the roasting is not the issue, the risk can come from what goes on afterward. Think, for example, of doing a great job of washing your hands, only to dry them off with a dirty towel. If a company does not have proper hygiene and food-safety protocols, their products are at risk anywhere along the line -- from the roaster to the final container. Recalls are designed to overcompensate and stop the outbreak while the food-safety detectives identify how the food was tainted and how it got into your store. Check the Food and Drug Administration website (fda.gov) for recalls, and watch for the brands you frequently buy.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Are there any health benefits from eating raw almonds, as opposed to roasted ones? Does oil roasting them add many calories from fat, compared to dry roasting? Also, is it best to store raw nuts in the refrigerator? -- T.N.P., via email

DEAR T.N.P.: Roasting nuts, or any food, for that matter, helps to bring about flavor-enhancing chemical reactions. This can be accomplished with or without the use of oil.

Dry roasting utilizes only hot air, and is done in specially designed ovens. Salt, paprika or other flavorings can then be added. Although dry-roasted nuts do not contain additional oils from the roasting process, this does not amount to a large difference in overall fat content. Half the weight of the raw nut -- and over 70 percent of its calories -- come from its oils. Honey-roasted nuts will contain less fat per serving, but only because some of their weight comes from the added sugars.

In terms of nutritional value, any high-heat process will destroy some thiamin (vitamin B1), but the other nutrients are relatively unharmed.

Nuts tend to be packaged in airtight bags or containers. They should be stored that way and kept in a cool, dry place to prevent mold and the slow oxidation of the oils. Refrigeration in a sealed container for raw nuts, or any nuts, makes sense as it effectively slows these damaging processes to an even greater degree. This is less of an issue if the nuts will be gone within a month after opening. But look to refrigeration if you want to store these perishable foods for longer periods of time.

DEAR DR. BLONZ: I appreciated your recent article concerning oils, but the term "room temperature" is vague. Please advise me of what you consider the temperature range for "room temperature." The reason for my request: My elderly parents keep their house between 85 and 95 degrees F, day and night, during our dry, hot, 100-degree California valley summers to save on electricity. Believe me, this is not what I consider a comfortable room temperature. My pleas to keep whole wheat flour and other whole grains, seeds and oils in the fridge during the long summer months fall on deaf ears, as they point out they have clearly been storing them at "room temperature." -- K.F., via email

DEAR K.F.: In the U.S., the temperature cited as "room temperature" is usually 68 degrees F, and the range commonly used is 68 to 72 degrees F. It is not a precise measure, and I have seen the range expressed in Centigrade as 20 to 25 degrees C (68 to 77 degrees F).

If one were in the tropics or in a desert climate in the U.S., room temperate would, of course, be higher. The guidelines for food storage in hot climates is different, as exposure at "room temperature" there would hasten spoilage. If there is no stated recommendation to refrigerate the product in question, it makes sense to at least store perishables in a cool place in the house. If there is no such place, perishables should be kept in the fridge. If this is not practical, my advice is to buy perishables in smaller containers. Please pass this on to your parents.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.