DEAR DR. BLONZ: Growing up, I was taught that too much white bread caused constipation. As an adult, I learned that wheat bread is good for us because it includes the health benefits of fiber. Does white bread actually cause constipation, and is wheat bread the better choice? -- K.J., New Orleans

DEAR K.J.: "Wheat" as a descriptor can be misleading, because it can refer to white, whole grain or a blend of the two. About 90% of the breads (and cereals) sold in the U.S. are made with refined, not whole-grain, wheat flour that has been enriched with niacin, riboflavin, thiamin and iron up to the levels found in whole-grain wheat flour. Nutrients naturally present in whole-grain flour include magnesium, zinc, vitamin B6, folate and fiber. These nutrients are not present in flour that's not labeled as "whole wheat" unless purposely added.

"Enriched" flour includes nutrients that are lost during processing and returned to their original levels. "Fortification" refers to adding nutrients not initially present in the food; one classic example is milk being fortified with vitamin D.

Foods considered to cause constipation slow their passage through the intestines. While it is made from little more than refined flour, leavening and water, white bread does not contribute to the unabsorbed bulk traveling through the intestines -- it does not slow things down.

When data about the health benefits of dietary fiber began to emerge, some bread manufacturers began to add dietary fiber to their white bread. It is best to check the nutrition label and the ingredient statement to see if fiber is present in your brand of bread. If, in fact, dietary fiber was added to that product, it would help keep things moving through the intestines.

Be aware that bread color can be deceiving. A not-whole-grain bread that looks like a whole-grain bread could be nothing more than enriched-flour white bread with added caramel (brown) coloring -- which would be shown on the ingredient list.

Those interested in a fiber-rich whole-grain experience should look for bread with whole wheat as the first ingredient. Those whole-grain products will contain all of the wheat's nutrients -- fiber included -- and contribute to your desired moving experience. (Read more about whole grains at b.link/fh2j8fw.)

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'm inquiring about the use of activated charcoal to help get toxins out of the body: how much to take and whether it works as a blood purifier. -- L.N., Anderson, North Carolina

DEAR L.N.: Activated charcoal, a purified form of charcoal ground into a fine powder, needs some explanation. Activated charcoal is not absorbed into the body; instead, it acts locally with whatever substance it comes in direct contact with. Its fine powder consistency gives it a large surface area to do its job, and its pure carbon composition attracts and holds onto substances using a process known as adsorbence (not to be confused with absorbance).

Adsorbency is why activated charcoal is used in water filters: It grabs and holds heavy metals, unwanted minerals and odors. Activated charcoal is often used in first aid after accidental poisonings, as it holds on to the poison and prevents it from getting into the blood. (According to a position statement of the American Academy of Clinical Toxicology, activated charcoal is more beneficial if administered within one hour of poison ingestion.)

It is unclear how activated charcoal could work as a blood purifier, because it isn't absorbed into the body. It can keep things out, but there is no evidence it can grab on to toxins already in the body. So unless your doctor instructs you otherwise, there is no reason to consume activated charcoal regularly. It can reduce the absorption of nutrients, but even more concerning, activated charcoal can adsorb medications, rendering them unavailable for absorption. (For more on activated charcoal, see b.link/r65ey55.)

DEAR DR. BLONZ: I drink three to four liters of sparkling (carbonated) water daily that I make from filtered tap water in a home device. I don't like regular water, so I figured this would give me my daily requirements. I often add fresh lemon or lime juice, but no sweetener. I don't drink any sodas.

I was on a plane recently, and after ordering soda water, the man sitting next to me stated that drinking carbonated water affects the nutrients the body absorbs because of the CO2 it contains, and now I'm concerned. I am health-conscious, eat well and work out regularly. Are even unsweetened sparkling beverages bad? -- A.H., Pomona, California

DEAR A.H.: Outside of causing a burp now and then, there is no evidence that the carbon dioxide (or CO2) in carbonated water -- also known as sparkling water or club soda -- causes any nutrient deficits. Albeit a bit more costly, drinking a carbonated mineral or spring water is a perfectly fine way to get your daily water requirements.

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: A holistic doctor featured at a recent wellness conference stated that pasteurization destroys a critical enzyme in raw milk that is needed to absorb calcium. Is this true? -- M.Q., Phoenix

DEAR M.Q.: There are enzymes in raw milk that are broken down by the process of pasteurization, so that part is correct. However, the real issue is whether these enzymes are critical for the body's absorption of the calcium in milk -- and the answer is no. The calcium in dairy has good bioavailability, and there is no clinical evidence that it is significantly better absorbed when consumed in raw versus pasteurized milk.

There are several enzymes in raw milk -- some are from the cow, and others are in the bacteria naturally present in the cow's digestive system. One milk enzyme produced by the cow is plasmin, a protein-digesting enzyme that degrades milk, causing spoilage. Anyone who has seen the clumps or mistakenly consumed spoiled milk can attest to its unpleasantness.

Pasteurization, while not a sterilization process, involves the application of heat to reduce the level of potentially harmful microorganisms that can cause spoilage or disease. It knocks out some, but not all, of the enzymes and bacteria, which allows the milk to remain wholesome through its projected period of storage and use. Refrigeration slows bacterial growth and enzymatic action, which is why milk goes bad if it's allowed to sit out too long. (There are extended storage periods for milk products processed at higher temperatures [ultrapasteurized] or packaged in aseptic containers. For more information on milk expiration, see b.link/qb4mmax.)

The lecture you mentioned sounds like an unscientific milk attack. Some people have no interest in milk, and others feel it is food only for calves. Dairy provides us a healthful package of essential nutrients, but not everyone wants to drink milk, and not everyone needs to.

DEAR DR. BLONZ: I read an article concerning the benefits of selenium, but it recommends taking yeast as a supplement. I seem to have an intolerance to the yeast in bread and cheese, which causes bad stomach pain. Does this mean I shouldn't take selenium? -- N.S., Tulsa, Oklahoma

DEAR N.S.: The selenium present in our foods depends significantly on the selenium content of the soils or waters in which they're grown. The same can be said for yeast, as the mineral will be present only if the yeast is allowed to grow on a selenium-rich medium. Typical food sources for selenium include seafood, such as tuna, clams, oysters and swordfish, nuts (especially Brazil nuts) and seeds, organ meats, and grains such as oats and wheat. (For more on selenium, see b.link/ebgbcf9.)

Selenium deficiencies are uncommon, but if you are looking for a supplement and are concerned about yeast, be sure to find one that's yeast-free. Finally, check with your health professional concerning the stomach pains you have been experiencing.

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.