DEAR DR. BLONZ: There have been a number of articles lately questioning the wisdom of taking vitamin and mineral supplements. And although it seems to be at cross-purposes, I have also read about the benefits of wheatgrass juice. The product literature states the body will absorb about 90 percent of the nutrients from wheatgrass, which is much more than other foods or pills. Is there any truth to this? Is this food a better source of nutrients than others? -- M.S., Spokane, Wash.

DEAR M.S.: There is no evidence I am aware of that the nutrients in wheatgrass are absorbed more efficiently than those from other whole foods. If by "questioning the wisdom of taking vitamin supplements" you mean questioning the wisdom of relying on supplements to provide all that the body needs, that is certainly something I am in agreement with. I have never recommended supplements as a primary source for nutrients. There is no basis to believe that a lousy diet can be made "healthful" through supplements. With few exceptions, preparing, eating and enjoying whole foods will always be superior. The exceptions might be when there are elevated or specific needs for certain nutrients.

As regards that rate of absorption for the nutrients in wheatgrass versus those in vitamin or mineral supplements, we need to assume that they are constructed so that they will be in solution by the time they reach the absorptive surfaces of the small intestines. Taking a supplement at mealtime aids this process. Supplement manufacturers should provide data to affirm that their products dissolve. In general, there should be a comparable rate of absorption between the vitamins or minerals in foods, and those coming from dissolved supplements. There are exceptions. The absorption of naturally occurring folate in foods turns out to be less efficient than that of the synthetic folate found in fortified foods and supplements. Vitamins tend to be more bioavailable, but minerals are not always efficiently absorbed.

The form a nutrient is in, and the presence or lack of key food components, can affect absorption. For example, calcium is more efficiently absorbed from milk or milk products primarily because the lactose in the milk enhances calcium uptake. The form of iron found in meat, known as heme iron, is more efficiently absorbed than the iron found in fruits and vegetables. Non-heme iron absorption is enhanced in an acid environment, such as that found in citrus juices or tomato sauce. Please don't fret over every last bit of absorption. It does, however, strengthen the argument for variety.

As for wheatgrass juice, it's definitely an acquired taste. Depending on how much is consumed, it can be a source of certain nutrients and it does contain phytochemicals, but I question any acclaim for it being "magical." If you are taking or considering this product, or a similar powdered whole food supplement, I encourage you to visit consumerlab.com to see their recent report on contaminants found in some of these products (tinyurl.com/l3yzswy).

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: Does vegetable oil mellow or otherwise improve with age? We have a number of bottles that we received as gifts but they have been sitting on the shelf for about a year and a half. They were in such beautiful bottles that nobody wanted to open them. Are they still ok to use if they have not been opened? -- J.L., Glendale, Ariz.

DEAR J.L.: Unlike wine, oils do not improve in the bottle. An extra virgin olive oil, for example, will be at its best when first put in the bottle (or can) and it's all downhill from there. Oils should be tightly covered and stored away from heat and light. An unopened container of refined vegetable oil that is properly stored can maintain its quality for about a year. Some oils, including extra virgin olive oils, claim they can last up to two years unopened. After being opened, if stored properly, you have about six months with most oils.

As a general rule, the more unsaturated the oil, the shorter the shelf life. Oils that have been sitting for questionable periods of time should get a sniff and a taste test before being used.

It is always best to buy your oil in containers that match your expected rate of use. If you end up buying in large containers, consider splitting the contents and putting half in the refrigerator for later. Select a container size that allows for very little air space atop the oil as it is stored. To help you keep track, mark the date of purchase, and the date the container was opened, on the label.

DEAR DR. BLONZ: What is taurine? I saw it listed as an ingredient in cat food and didn't give it much thought. Now I find that it is an ingredient in some of those energy drinks. I don't know what it is or what it is supposed to do, and was hoping that you could help. -- R.G., Bend, Ore.

DEAR R.G.: Taurine is a common amino acid, one of the building blocks of protein. Although needed by cats, it is not an essential amino acid for healthy human adults in that the body can make all that it needs. In addition, there are plentiful amounts in meats and fish. There is, however, some preliminary evidence that taurine at higher levels of intake may be of therapeutic value for those suffering from congestive heart failure. It is unclear what taurine adds to energy drinks, especially given the small amounts present in such beverages. 

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 it dangerous to eat an entire apple, including the seeds? One of my friends does this all the time, but I know there is cyanide in apple seeds. I have mentioned it and he said he has been doing it his entire life. -- H.N., Piedmont, Calif.

DEAR H.N.: You are correct about the cyanide. Apple seeds -- along with apricot kernels, peach pits, cherry pits and stems, and the leaves and roots of some rose family species -- are natural sources of the cyanide-containing compound known as amygdalin. Cyanide has an ability to quickly and effectively slow down body metabolism, so it can be a very potent poison. But as with most toxic materials, it is the dose that's the key.

The body has a recovery mechanism that can cope with small amounts of cyanide, and the relative amount of amygdalin in the seeds of one apple does not represent a significant health risk. There is little to worry about if you happen to eat the seeds while enjoying your apple.

Consider also that apple seeds have a rather tough seed coat that is difficult to digest. Most seeds pass through the digestive tract intact -- that is, without transferring any amygdalin to the person eating them. (Actually, this is a method of seed dispersal found in nature: An animal in one location eats the entire fruit and eventually expels the seeds in a new location.) Because whole-fruit blenders and juicers crush the seeds, and because multiple apples can be used in one serving, it would be prudent for those using these devices to remove the seeds beforehand.

DEAR DR. BLONZ: Does it become dangerous to drink orange juice once it has become slightly fizzy? How does this differ from carbonation? -- R.L., Berkeley, Calif.

DEAR R.L.: Fizz, when intentional, comes from carbonation, which is the addition of carbon dioxide gas (CO2). Carbon dioxide will not dissolve well into warm water, but it becomes more soluble as the temperature goes down. Pressure helps "hold" the gas in solution. This explains the "pop" and greater release of gas when a soda is uncapped at room temperature. At best, the carbon dioxide is only loosely held in the water, which explains why agitations such as pouring a warm soda over ice, or shaking the bottle, brings forth a gaseous eruption.

When you consume carbonated beverages, some of the swallowed gas can be absorbed and exits the body through exhaled air. The rest exits the body through belching, a process by which the esophagus opens and allows the pent up gas out from the stomach. If it manages to make its way past the stomach, the gas can pass through the GI tract and exit at the other end.

Fizz that develops in orange juice is a sign of spoilage due to microbial fermentation of the sugars in the juice. The fermenting organism gives off carbon dioxide gas that can be detected by your tongue, thus giving a sensation similar to that caused by carbonation. There will also tend to be a loss of sweetness during this type of spoilage since the fermentation organisms feed off the simple sugars for fuel. Because the spoilage organism is unknown and there is a potential health risk, it is best to discard the juice when you sense any type of unplanned fizz.

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.