DEAR DR. BLONZ: How long can vegetables such as carrots or broccoli be kept in the refrigerator without losing a significant amount of their nutrients? These are the vegetables we tend to buy regularly, always having them available for a meal. -- E.P., Oakland, California

DEAR E.P.: You have chosen a great pair of staples: ones that are available in most farmer's markets and grocery stores throughout the year, in most parts of the country. Depending on the way they are stored, you should have a week or two for the broccoli and about a month for the carrots, after which points both will have begun to experience decreases in their nutrients and flavors.

Carrots can lose sweetness as they sit, so purchasing carrots with fresh-looking greens intact can provide a good indicator of just-picked freshness. Once purchased, though, you should remove the tops, as the greens drain water and nutrients from the carrot. This makes perfect sense, given the fact that the portion of the carrot we consume is the root, which is the nutrient supplier for the above-ground greens.

Carrots store well in a refrigerator set no higher than 40 degrees F. They should be kept in a sealed plastic bag or container to prevent loss of moisture. They are at their nutrient and flavor peak in those first few days, and then begin to lose crispness and nutritional quality -- slowly for the first couple of weeks, but then quickly downhill until they become limp. If it gets to the point where the carrots become spotted or discolored, or get slimy, they are only fit for the compost bin.

Most of the carrots we get in the store are immature, being picked that way to maximize tenderness and flavor. More mature carrots often have a more "woody" texture, and while they might not have the same sweetness, they can be kept for longer periods of time. In pre-refrigerator days, root crops such as carrots were kept in root cellars for up to six months. Sustenance was the primary consideration in those times, and stored vegetables could always be incorporated into slow-cooked, flavorful stews.

Broccoli, similar to carrots, keeps best at low temps (35 to 37 degrees F), preferably in a high-humidity crisper drawer in the refrigerator. A perforated plastic bag is recommended to prevent wilting. Give your fresh broccoli a sniff and use that scent as a mental benchmark for later.

Count on broccoli keeping for up to a week or so, and possibly longer. Temperature is the key. At temperatures just above freezing (32 degrees F), broccoli can be kept up to four weeks. This drops to two weeks if the temperature is 41 degrees F, and only five days if the temperature is 50 degrees F.

Nutrient losses will be insignificant at first. Signs that things have begun to turn are new odors, signs of discoloration (yellowing), and a loss of the rigid texture that characterizes this vegetable. At that point, this broccoli should share the same fate as over-the-hill carrots.

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: I'm taking a dietary supplement that contains OPCs along with vitamins, minerals and herbs in an isotonic form. It is purportedly a more efficient delivery system, as it goes through the stomach and right to the small intestine, allowing for close to 95 percent absorption (since it's not diluted by stomach acid). Also, this speeds up the nutrients' entry into the circulatory system, occurring within five to 15 minutes, as opposed to the average four hours that a typical pill or capsule takes. What are your thoughts on this? -- G.C. San Diego

DEAR G.C.: Wow! Your descriptive statements certainly provide a supplement of puffery. They seem to be taken directly from promotional product literature. It is unclear whether there is any substantiation for these claims, or what extra benefits you stand to gain by taking such a product.

Ninety-five percent absorption for all nutrients? That's doubtful. The degree to which a nutrient is absorbed depends on the individual nutrient and a number of additional factors, including whether there is a deficiency (or an excess) of it in the body and in the diet. With many nutrients, only a small fraction gets absorbed even under the best of conditions.

You say your supplement's delivery system is "purportedly more efficient," but I would be interested to see any evidence supporting this claim. Pills, capsules or powders work just fine. As a rule, it's usually best to take vitamin and mineral supplements at mealtime. Digestion and absorption are designed to get the good stuff out of our foods by keeping the mass of food churning and in contact with the absorptive surfaces for an extended period of time.

For those interested, OPC is an abbreviation for "oligomeric proanthocyanidins." These are naturally occurring bioflavonoids found in grape seeds and skin, pine bark extract and other plants. They have been shown to perform as effective antioxidants and are currently being investigated for their role in protecting against chronic disease. But no one antioxidant can carry the entire load.

As with other lessons from nature, always consider the context in which the substance occurs. A whole food may contain a superstar nutrient with particular biochemical abilities, but it also contains a symphony of healthful components perfected over time to work together with that star. It is of questionable value to rely on a supplement without also having a healthful overall diet and lifestyle.

DEAR DR. BLONZ: I read with interest your article on the "milk effect" of putting tea in milk. It triggered this question of mine: Does adding half-and-half or milk to coffee also blunt coffee's antioxidant prowess? -- J.H.

DEAR J.H.: Great question. The phytochemicals in the coffee bean are a different family of compounds. They come from the bean (seed) portion, not the leaf, as with tea. They are not affected the same way.

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: I read that the best calcium supplements are made from bone. I have also heard that milk is not the best source of calcium because of the protein binding. What are your thoughts? -- R.T., Richmond, California

DEAR R.T.: Calcium hydroxyapatite is the key calcium compound found in bones. Because it is bone, it contains all the minerals found in bone, and somewhere along the line, someone came up with the idea that it would be an ideal calcium supplement. But calcium has to be absorbed before it can be utilized, and hydroxyapatite has yet to demonstrate its superiority as a calcium supplement.

Calcium carbonate is the most common form of calcium found in supplements, but if higher absorption is the key, the best bets are calcium citrate malate or calcium citrate.

The bottom line regarding calcium? It is more important to get calcium into your system than to spend time worrying over which form might have a few percentage points' greater absorption in a particular study. And regardless of which form you end up taking, it is widely accepted that the best time to take calcium is at mealtime.

You also bring up the issues of milk and "protein binding." Explaining the idea of protein binding in relation to calcium is a bit more complicated, so bear with me as I walk you through it. First, milk should not be the focus here. The primary issue is that when we consume more protein than the body needs, the excess does not get stored. Rather, excess protein gets directed to other uses. The bulk of protein's amino acids building blocks are converted into energy (fat), something we all know the body is quite efficient at storing.

Changing protein's amino acids into energy creates some metabolic refuse, and this must be eliminated from the body through the kidneys. Compounds being disposed of by the kidneys often grab "escorts" in order to leave the body through the urine. The refuse from the conversion of protein into energy tends to have a negative charge, and the kidneys must buffer this with something that has a positive charge; calcium can serve this purpose.

Calcium is not the first or only choice. In fact, there will be many other "positive" buffering compounds in any balanced diet that contains healthful amounts of fruits and vegetables. If, however, little else is around, calcium can get the call. When calcium leaves the body in this way, more calcium can be pulled from the bones to maintain the required level of calcium in the blood.

The bottom line is that some calcium can be lost when one eats a high-protein diet, but mainly when the diet does not contain the recommended intake of fruits and vegetables. The people who overdo it with protein, unfortunately, are often the ones who do not have a well-balanced diet.

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.