Dear Dr. Blonz: There was a great deal of publicity about mad cow disease a few years ago, including some distressing videos of suffering cattle and several tragic human deaths. We were advised to cook any beef products very thoroughly, or better yet, to avoid beef altogether. Then the matter dropped off the media world. What became of this topic, and do we still need to overcook all beef? What about products such as gelatin? -- P/RL, Berkeley, California

Dear P/RL: It is good that we haven't heard that much lately about bovine spongiform encephalopathy (BSE), also known as mad cow disease, as it is reflective of good science and effective controls. In people, the disease caused by BSE is a variant of Creutzfeldt-Jakob disease (vCJD), and it is a progressive, ultimately fatal condition that affects the brain and nervous system. Both BSE and vCJD are caused by an abnormal protein, referred to as a "prion," acting as an infectious agent. The term "prion" was coined by University of California San Francisco scientist Stanley Prusiner, who discovered this protein as an infectious entity and won the Nobel Prize for his efforts.

Your comment about cooking is misplaced given that high-heat exposures from cooking, boiling or even microwaving cannot reliably destroy the infectious nature of prions. While they are not airborne and not transmitted by casual contact, prions can be transmitted by contact with infectious bodily fluids or tissues, or the consumption of BSE-contaminated cattle products. The outbreak was first discovered in the United Kingdom in the 1990s, and once the source of the disease was uncovered, it led to the isolation and destruction of thousands of suspect cattle and the institution of rigid control measures.

Worldwide, 95 percent of cases have occurred in the United Kingdom. There continue to be strict import restrictions to prevent BSE-positive cattle from entering the United States. A history of the epidemic in the United Kingdom can be found at tinyurl.com/n9f7u6k. There is also information at the U.S. Centers for Disease Control (tinyurl.com/29zmmhl) and the Food and Drug Administration (tinyurl.com/2wvgxa3).

The risk of BSE led to valid concerns, not only about tainted meat, but about the use of cow byproducts.

Gelatin is a type of protein that can come from bones and hides of cattle, but it usually comes from pork. Irrespective of the animal source, the tissues used to make gelatin are considered by the FDA to be low-risk for the spread of BSE. In addition, the FDA published a guidance in 1997 that prohibits the making of gelatin from high-risk cows (tinyurl.com/nc8t45t).

We next consider the fact that the manufacturing process by which gelatin is made involves acid and alkali treatments and extensive washing coupled with high temperature sterilizations. Each of these steps further reduces risk. While it is always difficult to speak in absolutes, the process does make the risk negligible, and, as such, gelatin retains its "generally regarded as safe" designation as an ingredient in foods, or as an ingredient in medications or dietary supplements.

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: We have been shifting away from meat and making more vegetarian dishes lately. We're considering eating tofu, and I have a few questions. How much fat and other nutrients are in tofu, and how long should soybean tofu be expected to last? What is going on when it starts to change color, and is it no longer safe to eat at that point? Does tofu interfere with minerals in other foods? -- S.T., Sun City, Arizona

DEAR S.T.: Unlike other legumes, the soybean is relatively high in fat content; about half the calories in tofu come from fat.

There are a lot of steps to get from the soybean to the tofu. After soybeans have been soaked, crushed, cooked and filtered, calcium sulfate is often added to the soy pulp, which causes it to form a gel. Excess water is then removed as the soy gets pressed into cakes.

There are minor differences among different tofu makers, and there will also be variations between degrees of tofu firmness. But as a general benchmark, just under half the calories in tofu come from fat. A half-cup serving of firm tofu made with calcium sulfate (nigari) supplies 88 calories, 10 grams of protein, 2 grams of carbohydrate and 5 grams of fat (43 percent polyunsaturated). Other nutrients include 2 milligrams of iron (11 percent of the Daily Value), and 253 milligrams of calcium (25 percent of the Daily Value for adults). The calcium comes primarily from the calcium sulfate used to form the tofu into cakes.

Because of its relatively high content of polyunsaturated fats (PUFAs), tofu is susceptible to oxidation when exposed to the air for an extended period of time; the warmer the air, the greater the risk. As such, most tofu is kept refrigerated in water, or is vacuum-packed. When you purchase tofu, make sure it's stored in a similar manner. Tofu should be discarded if the storage water becomes cloudy, if a slippery film develops on the surface, or if you notice any unusual smells or tastes. Also, the tofu should be discarded if it takes on a pinkish tinge -- usually the effect of exposure to air. If the water is changed daily, fresh tofu can last up to two weeks in the refrigerator.

Regarding minerals, as long as it is consumed in moderation, tofu and soy milk are versatile, nutritious foods. Soy does contain phytic acid (phytate), as do other legumes and grains. This substance has anti-nutritional properties, in that it can bind with certain nutrients like iron and zinc and inhibit their absorption. This is a direct, physical effect that takes place in the digestive system; the ability to bind is limited by the milligrams of phytate present.

Tofu and soy milk contain phytates, and regular cooking doesn't affect the phytic acid that much. One way to blunt the phytate effect is via fermentation. This can occur in grains, as a yeast changes flour into bread. With soybeans, phytate gets broken down when the beans are fermented into products such as natto or tempeh.

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 recently that some people did a chemical analysis of white wines and found them to have five to 10 times the amount of arsenic that is allowed in an equal amount of drinking water. I was all set to throw my stash out when a friend suggested that we drink far more water than white wine, ergo the arsenic intake would not be harmful. Please offer your thoughts. Sincerely, B.R., via email

Dear B.R.: This is an evolving issue where there may be uncertainty over who or what to believe. Here is a brief background, and a number of links for follow-up. To start with, arsenic is a naturally occurring element (chemical symbol: As) that is distributed throughout nature. It tends to be present at varying levels in geological formations and, as a result, it can also be found in groundwater. It then is naturally taken up by fish and plants, and can also be found in animals that consume them. Arsenic is also found in various commercial products, including wood preservatives, fertilizers, paints, dyes and semiconductors. Various industrial practices, such as smelting and coal burning, release arsenic into the environment. Arsenic is considered a potent poison because it can interrupt essential reactions in the human metabolism. Acute overexposures can be fatal, but chronic exposures at sub-toxic levels can also cause problems. The U.S. Department of Health and Human Services has an information page on arsenic exposure (tinyurl.com/btcrc3o).

The toxicity of arsenic depends on its chemical (oxidation) state. Inorganic arsenic, which is found in geological formations, mines and groundwater, is considered the most toxic. Organic arsenic, which represents the forms of arsenic that have been taken up by plants and animals and made a part of their biochemical substance, is less harmful. (Depending on the circumstance, a plant, fish or animal can contain both forms at the same time.)

The human body has a means, albeit slow, to eliminate unwanted arsenic. The most critical element, of course, is to avoid the possibility of an acute exposure to a dangerous level of any type of arsenic. If the body experiences chronic exposures at a lower level, such as from the water supply, the key is to avoid an intake of the more-toxic inorganic arsenic that exceeds the rate at which the body can send it on its way. The half-life of inorganic arsenic in the human body is about 10 hours, and about 70 percent leaves via the urine. The Environmental Protection Agency sets limits for arsenic in drinking water of 10 parts per billion (tinyurl.com/3eu8sws).

Back to your question about arsenic in wine: There are some lawsuits filed, and when you toss in the possibility of litigation, everyone tends to shut up, save those who have a personal interest in a certain slant on things. What to do in the meantime? I found a number of accounts worth reading. The first, by National Public Radio, is informative and provides needed perspectives (tinyurl.com/o8jwkjs). Another is from Snopes.com, a site that strives to inject objective perspectives into various "urban legends" (tinyurl.com/q485ext). For those interested in a more scientific approach, there is a fact sheet from the University of California at Davis with specific ranges and implications(tinyurl.com/krrbls8).

As one who enjoys a glass of wine, I will continue to follow this issue.

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.