DEAR DR. BLONZ: How real is the danger from the lead content in calcium supplements? One company promotes its products by saying it contains no lead, but it is unclear how much of an issue this is with other (less expensive) supplements. -- F.R., Phoenix

DEAR F.R.: Some natural sources of calcium do carry a risk of lead contamination when they are used in supplements. These include bone meal, oyster shell and dolomite.

When a body is exposed to heavy metals, such as lead, and if the contaminant is coming in at a greater rate than the body can cast it off, the bones become an inadvertent holding location. As a practical example, animals allowed to graze near sources of industrial pollution can end up with higher-than-normal levels of contaminants in their bones. If these bones are then used to make bone meal for dietary supplements, there is a risk of the unwanted elements ending up in the bottle.

The same argument can be made for oyster shell calcium, if the oysters live in contaminated waters. Dolomite, also called dolomitic limestone, is a mined mineral that's composed primarily of calcium carbonate and magnesium carbonate, plus some other elements. If the mineral happens to be in areas that contain elevated amounts of lead, this natural source could also contain a natural contaminant.

These scenarios do not mean that products made from natural sources will automatically be contaminated. But if you choose a calcium supplement sourced from any of these compounds, you should only select a brand that specifically tests and states that their product is low-lead or lead-free.

DEAR DR. BLONZ: I noticed a bread label that read "stone ground wheat bread," but upon closer inspection, I found it to be white bread with molasses coloring. Is this sort of misleading labeling illegal? -- G.T., Hayward, California

DEAR G.T.: Wheat bread is made with wheat flour, and it can be white, whole-grain or a combination. A 100 percent whole-grain wheat bread tends to tout its "100 percent whole wheat" or "whole wheat flour" content. One of those will be the first item on the ingredient statement and there will be no other flours listed.

All wheat flour is made from ground wheat, and "stone ground" says nothing about any "whole-grain" character of the bread. It is somewhat misleading when a bread that is not whole-grain uses colorants to make it appear as though it is. Molasses can be used to provide some nutrients and help make the bread less crumbly. It is not a legal (regulatory) issue as long as the bread is not claiming or implying that it is whole-grain when it's not.

DEAR DR. BLONZ: Do the X-ray security machines in airports negatively affect the vitamins or medications packed in my luggage? Does it destroy their effectiveness? -- T.T., Boston

DEAR T.T.: There is no evidence of negative effects on dietary supplements or medications from the routine use of security machines in airports.

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 am in my junior year of a nutrition and dietetics program, and I am confused as to what path I should take for graduate school. I could see myself working for a food company -- developing, testing and promoting food products, and creating and testing recipes. If I pursue that, would it be more beneficial to focus on food science or nutrition? -- S.T., San Diego

DEAR S.T.: I often receive questions from students interested in the fields of nutrition and food science. A dietetics degree (R.D.) could certainly serve you well, but seeing as you are interested in working in the food industry, a food science degree would also seem to be a logical pursuit. Along with learning essential information about the science of food production, you would be more marketable when it came time to look for a job. You might consider a grad school that has both a food science department and a nutrition department (at some universities, these departments are combined).

I would recommend you check out the Institute of Food Technologists (ift.org), the professional organization for that industry. The group is based in Chicago. IFT's website offers information about careers in the food industry. Also, consider attending one of the many trade shows put on by the food industry. This would provide you with some excellent exposure to products, approaches and opportunities. IFT has an annual meeting, but there is also the Fancy Food Show (specialtyfood.com) and a host of others.

Whatever schools you are considering, I encourage you to ask for a list of the research interests of the faculty. Academic department success relies on the strengths of its faculty, and this is a good way to see how a department is oriented. Look for a school with faculty members whose interests are aligned with your own. I wish you well with this important decision.

DEAR DR. BLONZ: Is there any value to be gained from drinking wheat grass juice? Is this a reasonable thing to do if I do not have enough vegetables in my diet? -- J.J., Berkeley, California

DEAR J.J.: Supplements are not a substitute for healthful eating. Drinking wheat grass juice will only provide a modicum of nutrients, along with some healthful phytochemicals. Aside from testimonials, there is little in the way of evidence to support its benefits.

If you try it, you will notice its unsurprising "grassy" taste. Find an organically grown product, if at all possible. Feel free to drink it if you like the taste, but it isn't a go-to product that will cancel the impact of poor food choices. Ending a cheeseburger-and-fries dinner with a shot of wheat grass juice doesn't make it all better.

Then there's the fact that these supplements are usually quite costly. All in all, I encourage you to rethink the juice and strive to eat more vegetables instead.

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: Can you help us understand the World Health Organization's (WHO) announcement on cancer and meat? Did the WHO study control for processed meats with and without nitrites? A nutritionist once told me that vitamin C blocks the formation of cancer-causing nitrosamines, and that if I choose to eat bacon, I should also have a lot of orange juice. -- M.C., via email

DEAR M.C.: One study I recall from graduate school revealed that physicians who ate more meat and consumed more alcohol had a one-third lower risk of dying in a plane crash. Does this mean it would have been beneficial to encourage doctors to grab a burger and a beer before they boarded a flight? Needless to say, we need to understand a plausible mechanism before we can give full credence to any population study.

The announcement from the World Health Organization provides useful, but not surprising, information. At the same time, it reflects problems inherent with population studies that extract and correlate data on the impact of a single class of food. With such efforts, there is no way of knowing what was in the rest of people's diets, or the general health status of the individuals from whom the data was collected.

The WHO pronouncement, which covered meats in general, came after a review of hundreds of studies, each with its own methodology. There was a comparison, on a spectrum of health statistics, between people who ate no meat and people who ate lots of it -- and everyone in between. Find a significant difference along that gradient and you have an "association" to report between the level of meat intake and the risk of disease.

Here, we must ask if the key factor is all meat, or only processed meats. Or, does meat only become an issue when paired with a less-than-optimal intake of healthful foods? Or a progressively unhealthful, more stress-filled lifestyle? Or an interaction of these and other factors? It is difficult to control for such fine points, and population studies are not able to report cause and effect.

It is predictable that, analyzing the spectrum from no- and low-meat intakes up to hefty daily doses of the stuff, a general theme would emerge that excessive meat consumption is risky business. Many news stories left off all qualifiers and simply pronounced that "meat causes cancer," period.

A healthful diet, lifestyle and attitude are powerful mitigating factors against potential negatives, but when it comes to food, there is only so much room in our stomach. If meat is on your menu, then enjoy it, keep a handle on the portion size and don't lose sight of your plant-based, whole-foods perspective.

As for your mention of preservatives, fresh meats are less risky than nitrite-preserved meat. Nitrites can combine with the amino acids in meats to form cancer-causing nitrosamines. Vitamin C can help inhibit the formation of nitrosamines, but having orange juice with bacon shouldn't be considered a fix. Routinely having fruit or berries at any meal is always a positive.

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.