DEAR DR. BLONZ: Besides fresh and frozen vegetables, I often use canned, especially tomatoes. I buy organic when available, and periodically they are imported. I recall lead solder used to be used in many brands of canned foods, mainly the imported ones. This type of solder seemed especially dangerous for acidic foods like tomatoes. Does the fact that the can is airtight make it safer, or are protective substances added to make it so the food won't react with the metal? -- F.S., San Jose, California

DEAR F.S.: Cans used to be made in three pieces: top, bottom and the cylindrical body, all soldered together into the familiar shape. Lead is an ideal soldering material, but its use where there would be contact with foods turned out to be risky business when we learned of its toxic effects in the human body. Lead is hazardous during pregnancy, infancy and childhood. (Read more about lead poisoning from the National Library of Medicine at b.link/c5yt9r.)

Domestically produced cans were the first to stop using lead solder; canned food manufacturers in the U.S. reported having stopped using it by 1991. Cans are now welded together or extruded into a two-piece shape that eliminates the need for the side seam. In all cases, the can materials are formulated to inhibit the leaching of metal ions into the food -- even when the goods inside are acidic. This sometimes involves using an enamel or vinyl liner substance designed to not react with the contents.

Food companies in developing countries have moved toward lead-free cans, but it is difficult to say that all are there yet. For those cans, the Food and Drug Administration has an action level of 250 parts per billion of lead in the food, a level considered to be safe. If a can exceeds that level, it can be seized by the FDA.

Although this may provide some comfort, it's not a safety guarantee. It is prudent to check the labels on any imported canned food, especially if it is one you would be purchasing on a regular basis. If there is no information on the label or product website, check with the supplier. Another option is to use test kits with swabs that turn a particular color when exposed to lead. These inexpensive kits, good to have around the house, can be used on cans, pottery, crystal, pitchers or any food-contact surface you want to examine.

While not raised in your question, another substance raising concern in food containers is bisphenol A, known as BPA, which is often used in can-lining materials. (Learn more about BPA at b.link/dzukfd.) The FDA regulates how much BPA can be present, and no longer permits its use in packaging and containers that will hold materials for infants. Manufacturers continue to phase out the use of BPA in cans; for more, see an article from the Environmental Working Group at b.link/48wu35.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 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 would like your help to settle an argument at a recent dinner. There seems to be such a push to restrict salt consumption in general, but the only hazard I am aware of is that salt can raise blood pressure in some people. Is there any other risk associated with salt, aside from high blood pressure? -- H.T., via email

DEAR H.T.: The main issue with excess salt intake is, as you mention, its association with high blood pressure (hypertension). But this is nothing to be dismissive about. High blood pressure currently affects roughly half of adults. It's called "the silent killer" because there are no warning signs until problems such as heart disease, stroke or kidney disease have already developed. The only reliable way to determine whether you have hypertension is to check your blood pressure regularly.

Salt and sodium are not automatically antagonistic for everyone, even those with high blood pressure. But there is no health benefit from excessive salt -- only liability. For those at high or uncertain risk about their blood pressure, it is best to keep salt to a minimum. Another point to consider is that one's sensitivity to salt, and ability to consume it safely, can change over time.

Finally, saltiness is one of our basic tastes. Salt helps to bring out the flavors in food. But the point should be to enjoy the natural flavor of foods, rather than that which comes from the salt shaker. Consider it a warning sign if you routinely reach for the shaker before you taste the food.

See b.link/2qkdb4 for more on high blood pressure.

DEAR DR. BLONZ: I work with second and third graders as a student teacher. We would like to know: How do scientists determine the levels of protein and other nutrients in fruits, vegetables, meats or processed foods that contain them all? And where can I take my students to show them scientists analyzing foods? -- T.T., Chicago

DEAR T.T.: To analyze foods, representative samples are put through a series of laboratory tests that measure the amounts of macronutrients -- such as protein, fat and carbohydrate -- and micronutrients in the item. ("Macro" means larger amounts of the nutrient, whereas "micro" means smaller amounts. Read more at b.link/33chvc.) Each nutrient has its own test. Independent laboratories around the country perform these analyses, although food companies often have their own labs, as well.

You should check in your area for food manufacturers with in-house labs that offer tours. Consider creating a list of options and allowing the students to vote for their selection. I grew up in the Chicago area, and a trip like that was one of my most memorable class outings. I predict you will find companies willing to open their doors to your students.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 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 READERS: You may have noted an increased number of self-proclaimed "experts" making dubious diet and health claims lately. These tend to come from those who eschew any obligation to be evidence-based, and their pronouncements often spread like weeds on social media. This is not what you want when looking for objective, reliable explanations for serious health issues; it is particularly dangerous during a pandemic's added stresses and complexities.

It helps to understand that scientific research is a complex cuisine, with the principal investigator serving as the equivalent of an executive chef. Unlike preparing an evening meal, research is a process that takes years to plan, conduct and analyze before any results are ready for consumption. Funding is pivotal; it governs what gets done, who will be available to do the work and, in the end, how the "serving" of science gets digested by the public.

Scientists at research institutions rely on grants from federal and private sources to keep their laboratories in operation. Competition for limited funds continues to increase, and the situation shows no improvement. Grant applications are reviewed by scientists selected for this purpose; the agencies distribute their funds according to priority scores assigned during evaluation. Many turn to industries and grant-giving foundations for their funding. This can mean looking at an issue from a different perspective: usually, one of interest to the organization writing the check. For many scientists, grant-writing takes up a big chunk of time. Some take courses on how to write better grants. Others form collaborations with scientists who have a better funding track record.

This reality behind scientific research is rarely understood or appreciated, and it helps explain what might come across as the conservative nature of mainstream science. How can one justify pursuing ideas on the fringes of science when such pursuits have a lower likelihood of funding? Consider, also, that challenges to mainstream thinking may place an individual at odds with the senior faculty members who will preside over their academic tenure (aka secure employment) decisions.

Even if initial research dollars are received, tackling new concepts can yield unclear results in the opening experiments. This can limit publishable results and affect the chances of a grant renewal. Scientists often opt to conduct smaller pilot experiments to help them design a better study; these can produce results more rapidly, while letting them know whether their theories make sense. Positive pilot study results can affirm theories, help with experimental design and increase the odds of future funding.

The message here: Don't assume that any questionable theories you hear have been put through the controls and constraints of the scientific process. To be our own best advocates, we each must ensure that the people providing advice are the real deal. If they're passing themselves off as experts, look into their training and education; find their peer-reviewed publication record; research who they work for. What are their accomplishments, outside of promoting a particular take for an organization or selling products claiming to provide a needed fix?

Stay away from those without appropriate academic and clinical training in the sciences. Simply because an individual claims mastery over their own experience with a health issue does not make them an expert for others facing the same challenge. If they present new concepts, be sure they provide support from objective, independent, science-reliable (preferably academic) sources.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 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.