DEAR DR. BLONZ: I am interested in your thoughts on pesticides and organic fruits and vegetables. What are the dangers of foods grown using pesticides, and what is your view of the benefits of the alternatives (such as buying organic)? -- N.T., San Diego

DEAR N.T.: Health experts consider the hazards from pesticides to be well behind other dangers in our food supply, such as bacterial contamination and naturally occurring toxins. However, pesticides still do pose a challenge. One alternative is organic agriculture, where foods are raised without synthetic chemicals, such as pesticides, herbicides or fungicides. Another, called integrated pest management (IPM), limits the use of synthetic chemicals whenever possible, although they remain a part of the farmer's arsenal to be called upon when needed.

Farmers' markets can be a great source for organically grown fruits and vegetables or those produced on farms that practice IPM. There are an increasing number of supermarkets that offer these foods as well.

The discussion of organic vs. conventional agriculture needs to go beyond the safety of the foods we eat. Such concerns must also include the risk to workers who manufacture, transport and apply these powerful chemicals, and to our environment. All this helps to explain why, despite assurances, survey after survey reveals that American consumers continue to be wary of pesticides.

We are the best-fed country in the world, but this status comes with a tremendous price tag in natural and human resources. Billions of pounds of commercial fertilizers are used annually, and the use of pesticides made from petroleum to control weeds, insects, diseases and other pests helps explain why farming uses up more oil than any other single industry.

America's preoccupation with perfect-looking produce is a factor behind the continued demand for pesticides. A 1998 report out of the National Academy of Sciences titled "Alternative Agriculture" detailed how the food industry encourages the use of pesticides solely to maintain high cosmetic standards. A survey conducted on citrus fruits by Public Voice and another by the American Farm Bureau Federation found that, in some cases, over half the pesticides used are for purely cosmetic reasons, such as to prevent minor external blemishes that had nothing to do with the taste or wholesomeness of the fruit.

To eat, or not to eat, should never be the question. No one wants to impair our ability to feed the nation. The focus should be on the direction agriculture should be heading. We all need to balance human needs with costs and environmental consequences. Agriculture cannot continue to operate using environmental "deficit spending." Today's output should not mean a loss of tomorrow's resources. There needs to be a course that guides our agricultural environment back to health without impairing our current capabilities. Ideally it would be a balanced, sustainable system that gives back as it takes.

Information is power, so I encourage additional reading. The EPA has a page on pesticides at epa.gov/safepestcontrol. I also encourage you to check out the FAQs at the nonprofit Organic Farming Research Foundation: ofrf.org/organic-faqs.

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: What does the "L" stand for in L-arginine? Is it the same thing as plain old arginine? I have also seen this letter on other amino acids such as ornithine. -- L.T., Santa Rosa, Calif.

DEAR L.T.: The "L-" or "D-" before a chemical substance reveals something about the compound's three-dimensional structure. To be more specific, it refers to the optical rotation of the substance, and while this may seem like a subtle structural difference, it has definite effects on how the compound can be used chemically and in the body.

We use "L" amino acids in the synthesis of our proteins, and they are found in the protein foods we eat. "D" amino acids have no nutritional value for humans. As you indicate, the "L" might be left out in some writings. It is a bit less precise, but it saves the need for this explanation. On the "D" side of things, we have D-alpha-tocopherol (vitamin E); in this case it is the "D" version that's the active substance. One final point: If both a "D" and an "l" are noted together, as in "Dl-alpha-tocopherol," this is usually a sign the compound has been made synthetically.

DEAR DR. BLONZ: I take a calcium supplement that contains calcium carbonate along with magnesium and vitamin D. I have been advised by a close friend that calcium carbonate is the least absorbable form of calcium, and that I need to switch. My question is whether the presence of vitamin D makes up for this and helps with the calcium absorption issue. Are the other forms of calcium still more absorbable than calcium carbonate, even with vitamin D? Thanks for any light you might shed on this issue. -- N.N., Phoenix

DEAR N.N.: First, on vitamin D: Having it in the same pill with calcium doesn't enhance the absorption of the calcium in the pill, but our body definitely needs adequate vitamin D to produce its "calcium-binding protein." That's the protein made by the body that attaches onto dietary calcium in the small intestine and facilitates its absorption. This makes vitamin D an important part of the big picture, but it doesn't need to be in your stomach at the time as the dietary calcium.

We do find vitamin D in calcium-containing foods (it is added to many dairy products), and as you indicate, it's not uncommon to find it as an ingredient in calcium supplements. The body makes its own vitamin D when it is exposed to sunlight (about 15 minutes per day on the face and hands is plenty). Seniors, particularly the homebound elderly, are at risk for a vitamin D deficiency because they don't often get out into the sun.

As regards your supplement, don't be that concerned about it being a calcium carbonate product. People always seem to yearn for "The No. 1 Best Supplement," but in the case of calcium, the degrees of improvement from one form of calcium to another are not significant enough for you to toss your pills. You will be fine as long as you take it regularly -- ideally at mealtime or with an acidic beverage, such as orange or tomato juice.

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: Is there more vitamin A in dark-colored vegetables than lighter-colored vegetables? There is a debate in our class. -- M.H., San Jose, Calif.

DEAR M.H.: There is no pre-formed vitamin A in fruits and vegetables; rather, plant foods have compounds that the human body can convert to vitamin A as needed. The key players are the carotenoids, a group of colorful compounds that range from yellow to deep red. Any food's vitamin A potential depends on the carotenoid present, as not all can end up as vitamin A. For example, lycopene (red), lutein and zeaxanthin (yellow-orange) do not get changed into vitamin A.

Let's look at a group of vegetables to see how much vitamin A they provide per serving, first on a weight basis (vitamin A per unit weight), then on a calorie basis (vitamin A per calorie). Our eight representatives are all examples of healthful foods and excellent dietary sources of carotenoids. They are: fresh spinach, basil, kale, carrots, and leaf lettuce; baked sweet potato; canned pumpkin; and dried pasilla peppers.

Taking portions of identical weights, they rate, from highest to lowest: dried pasilla peppers, sweet potato, carrot, pumpkin, kale, spinach, lettuce, basil.

Viewing this same list on vitamin A per calorie, the highest to lowest are: lettuce, pumpkin, carrots, spinach, kale, sweet potato, basil, dried pasilla peppers.

In both cases, there is a slight straying from any conclusion that dark equals more vitamin A. Perhaps the issue is that your discussion was limited to one known nutrient. Eating foods rich in natural colors is a great goal, and their presence tends to signify a richness of natural, healthful phytochemical compounds.

You can get additional information on the nutrient content of foods by visiting the USDA database at ndb.nal.usda.gov.

DEAR DR. BLONZ: I just read an article about potatoes, and I am a bit concerned. I just bought a bag of organic Russet potatoes, and they sprouted very quickly. I have been pulling the sprouts off, and the potatoes don't appear terribly green. Are these still harmful to consume? I would not prefer to waste five pounds of organic potatoes! -- K.S., via email

DEAR K.S.: You might consider returning them, especially considering that you "just" bought them. But if there is no green on the potatoes, and they are still firm, you can remove the sprouts and a bit of the sprout base and it should be fine. One issue with the alkaloids present in green potatoes (solanine) is the dose, so as long as they are only for a side dish, there should be no problem. Potatoes should be stored in a cool, dark place and you shouldn't get more than you would expect to eat in a week or so. One issue is that you don't know how long the potatoes were at the store before you bought them. Always give produce a good inspection before you put it into your cart.

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.