DEAR DR. BLONZ: Are some calcium supplements better than others? I had been using oyster shell calcium, but read there are risks of a contaminant. Is this form safe? -- B.B., Milwaukee, Wisconsin

DEAR B.B.: Calcium supplements from natural sources are the ones at higher risk for lead contamination, mainly because they tend to form in areas where lead is also hanging around. These sources include oyster shell, dolomite and bone meal.

Oyster shell calcium can become a problem when the oysters developed in lead-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 would also have its share of this unwanted mineral.

Bone meal makes sense as a calcium supplement because, in addition to the calcium, it contains the other trace elements used to make bones. The problem is that an animal’s bones often serve as storage tissue for heavy metal contaminants in the diet. Animals allowed to graze near sources of industrial pollution can become sources of higher-than-normal levels of these contaminants in their bones and other tissues.

This doesn’t mean that all natural sources are contaminated; it is just to let you know that when you choose a calcium supplement made from any of these compounds, you need to check the source. That means verifying that the company providing the supplement has tested their product and can provide assurances of its purity. Opt only for those brands that state their product is low-lead or lead-free. In general, only purchase supplements that provide you with the quality assurances that you, as a customer, need in order to be comfortable.

DEAR DR. BLONZ: I appreciate your science-based, respectfully written column, and never miss it. But I have a small correction to a recent answer about chelation therapy. You stated that the EDTA in lavender blood-collection tubes prevents blood from clotting by chelating the iron. Actually, it chelates the calcium in the plasma; the iron in cells is not accessible to the EDTA because the cells remain intact. -- E.B., retired clinical lab scientist, via email

DEAR E.B.: Thanks much for this correction.

DEAR DR. BLONZ: I was surprised when I read that the pH of lemon juice was actually lower than that of vinegar, making it more acidic. I can drink lemon juice straight, but vinegar takes my breath away. I have always been under the impression that if I substituted lemon juice for vinegar in a dressing or recipe, I should use slightly more lemon juice, which now seems unnecessary. -- B.G., San Diego, California

DEAR B.G.: pH is a measure of acidity, and it does not necessarily equate with taste. The vinegar used in foods comes from acetic acid, a substance that is produced during spoilage. It is pure acetic acid, so your taste buds get a real shot of that one component. In lemon juice, we have citric acid with a few other organic acids, but there are other flavor qualities to balance out the sensation. Vinegar acidities can vary, but most are about 5 percent. Lemon juice is in the same range. Your reactions make more sense when you consider the larger flavor context.

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: Does the fact that muscle weighs more than fat explain the annoying fact that I tend to gain weight when I exercise? -- S.M., Hayward, California

DEAR S.M.: Let’s first acknowledge the obvious: that a pound of muscle weighs the same as a pound of fat. There are differences in caloric density, which is the number of calories (energy) per unit weight. A gram of fat contains nine calories, over twice the four calories in a gram of protein or a gram of carbohydrate. (A gram of alcohol, for what it’s worth, contains seven calories.) Using a monetary analogy, a $10 bill weighs the same as a $5 bill, but the 10 has twice the “spending energy” as the five.

The answer to your question lies with the fact that we are water-based organisms. Fat is the most concentrated form of energy in the human body, and adipose tissue, which is where fat is stored, contains very little water. By contrast, the protein that makes up our metabolically active muscles and organs is mostly water. The body prefers not to waste energy, so it will only have around the amount of muscle needed to maintain the status quo.

Whenever our routines become less active, the body will slowly reduce its muscular mass down to the basic level needed to keep the show going. When our routines or exercise habits involve an increased muscular demand, the body will respond by increasing its muscle mass. Other adaptations to regular increased muscular demand include an increased vasculature (blood vessels) and blood volume to carry the nutrients and waste products, and increased ventilatory capacity to deliver oxygen and remove carbon dioxide as needed.

Let’s assume you are eating a fixed number of calories when you begin an exercise program. As your body experiences the stress of exercise, it responds by making new muscles to handle the load. It also makes all the other supporting tissues and fluids -- all of which are primarily water. This means that the numbers on the scale can go up slightly, but realize that it is mostly water weight you are gaining. You are not getting fatter, but home scales do not provide that breakdown. (For this, you need to do a body composition test.)

If you were to stop exercising, you might lose weight. But again, it is water you are losing, and you might be getting fatter (increased percent body fat) at the same time.

Focusing solely on the scale can be discouraging and misleading, because it does not give you the complete picture, even when good things are going on inside. And never forget that additional muscle mass means that more energy is being burned, even while you are at rest. Think about an 8-cylinder engine versus a 4-cylinder engine, with the larger engine burning more gas even while idling.

Becoming fit is the way to go. It improves your general health and enhances your body’s ability to handle many types of stress.

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: You tend to go negative about products sold through network marketing. In my view, if a particular product has health benefits, these marketing programs allow people to join a company, help their friends and others, and make a profit at the same time. It is such a natural way to help and participate, and I am troubled by your typical rejections. -- S.T., Casa Grande, Arizona

DEAR S.T.: Any nutritional product sold should be able to support its claims with published research in real-world situations. I search for evidence that the directions for use and amounts provided are consistent with the claims being made. These claims are the ones that tend to attract prospective customers (and network marketers) in the first place.

Consider the regulatory context -- namely, that there is none. There is currently no regulatory requirement that dietary supplements demonstrate they are safe, or that they work as claimed, before they are marketed. If misconduct is suspected, the companies can be challenged by those charged with consumer protection, such as state attorneys general, the Federal Trade Commission or the Food and Drug Administration. But the up-front bill is paid by the taxpayer, as these challenges occur AFTER the product is already on the market.

I consider it a red flag when there is no objective evidence, but plentiful praise from those profiting from the sale. We must decide for ourselves, and mine is not an automatic condemnation. If you or a loved one has taken a product and it has appeared to have worked, it would be reasonable to consider joining the company and spreading the word. Ideally, a profitable business entity of this type would invest in independent (not in-house) research to test all their claimed effects. I encourage you to inquire if this has been done at the company you are considering. For more on network marketing, check tinyurl.com/q9dw95b.

DEAR DR. BLONZ: I have had a run-in with health issues, and I am attempting to make changes. I recently began taking a statin, but I confess to craving meat, eggs and cheese. With the pills, my cholesterol numbers have improved, but I am not confident that things are actually getting better. -- S.E., Hayward, California

DEAR S.E.: I have heard many express a “craving” for certain foods that had a central place in their diet. Many are successful at slowly transitioning from one style to another as they integrate a big-picture understanding of the connection between diet, activity, health and longevity. I am not talking about your physician telling you to cut back on meat or fat as an end in itself; I refer to gradually gaining an appreciation for how eating a healthful variety of foods contributes to health.

We are so over-specialized in this country. While there are exceptions, dietary changes usually don’t have to be all-or-nothing. What we have become good at is throwing a pill at a problem to make it go away. There is a definite interconnectedness that needs to be understood, and once you gain that essential bit of savvy, you will realize that you can eat the foods you love as long as your diet and lifestyle are in good shape. My advice is that you take the time to educate yourself. Read more about nutrition and health. Stick around, and I will attempt to push you a bit further along on that road.

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.