DEAR DR. BLONZ: At a recent lunchtime discussion, someone strongly stated the opinion that we should not mix proteins and carbohydrates at the same meal. They also said we should always eat fruit all by itself. I expressed general skepticism, but the person offering this was very intelligent; I was not certain exactly how to counter these arguments. -- A.M., Santa Clara, California

DEAR A.M.: This "don't mix food types" argument is not new. It is based on the dubious "theory" that it is not so much the foods themselves, but the way they are combined, that holds the key to health.

Such ideas appeared in a 1922 book titled "Mucusless Diet Healing System" by Arnold Ehret. There have been many reincarnations since, the classic one being the 1951 "Food Combining Made Easy" by Herbert Shelton, who started Dr. Shelton's Health School in San Antonio, Texas.

According to this notion, easy-to-digest foods such as fruits or other carbohydrates should never be eaten with proteins or fatty foods, which take longer to digest. To do so would delay the digestion of the carbohydrates, and in the case of fruit, allow the fruit sugar to ferment and putrefy as it waits its turn. The theory then imagines that this is responsible for today's health issues.

Other forbidden combinations include starchy foods, such as bread or potatoes, together with proteins, such as meat or fish. The theory stems, in part, from the fact that the body uses an acid (low pH) environment to digest protein, while it relies on an alkaline (higher pH) environment to digest carbohydrates.

There might be more interest in the theory if all the foods we ate were digested in the same location at the same time, but this is not the way it works. There are separate digestive enzymes for the proteins, carbohydrates and fats in our foods, and they operate in different regions of the digestive system. The treatments given to one type of food do not interfere with the others.

Protein, for example, is first denatured in the stomach by subjecting it to an acid environment. This, plus the churning by the stomach muscles, helps to break down the protein tissue so that the digestive enzymes will have an easier job. Once out of the stomach, the body neutralizes the acid; the rest of the digestive process, including the digestion and absorption of protein, carbohydrate and fat, takes place in a more alkali environment. If starches are present in a protein-based meal, they just hang out, waiting for their turn. The idea that they would ferment makes little sense -- especially in light of the fact that the acid environment of the stomach is not conducive to fermentation.

No doubt, many of us have found that certain foods or food combinations work best for us, and our bodies do seem to get used to the way we eat. But this is more a product of habit-bred efficiency than a requirement of the human species. There appears to be no physiological reason that we have to refrain from including a variety of foods at every meal.

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 recently purchased a bag of grated mozzarella cheese at a warehouse store. I had expected the ingredient list to read "milk, salt, enzymes," which is what you find on blocks of cheese. But this bag also included "natamycin to protect flavor" and "powdered cellulose to prevent caking." What is natamycin? Do I need to be concerned about either of these ingredients' effect on health? -- D.D., PhoeniX

DEAR D.D.: It can be troubling to see unknown ingredients on a food label: You're not quite sure what they're there for, and if they have imposing-sounding names, it is reasonable to be concerned that they might be unwholesome. Such ingredients, however, often sound more onerous than they actually are.

Natamycin is a naturally occurring antifungal preservative compound that can be used to help prevent the growth of undesirable molds or yeasts on cheese. It is used with certain cheeses because it doesn't work against the friendly bacteria that are essential for flavor development during the ripening process. It will most commonly be found on grated and sliced cheeses, due to their increased surface area. (This is one reason I prefer to buy blocks of cheese, then slice or grate them as needed.)

You can find products that don't contain this preservative, but it is doubtful that it is cause for any significant concern. The small amounts used act locally and, along with the protein in the cheese, will be denatured and destroyed during the digestive process.

The powdered cellulose is there to prevent the grated mozzarella from clumping together. This is a naturally occurring carbohydrate from plants. Cellulose, which is not digested, is the most plentiful carbohydrate substance in nature. It is actually considered to be dietary fiber, but the tiny amount needed for anti-caking won't even register on the food label.

Regarding food additives in general, you can limit the problem by sticking to whole, or minimally processed, foods. But even this is no guarantee. As a group, food additives are a mixed lot, containing a variety of substances that accomplish some rather amazing things. They are all chemicals -- one and all -- but the same can be said for all foods we eat, whether they come fresh from the garden or from a package on your grocer's shelf. The Food and Drug Administration has a reference on food additives at tinyurl.com/aub75ck, and there is another one at the U.S National Library of Medicine: tinyurl.com/hh84vuq.

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 have a low, steady ringing in my ears. It's more noticeable at night, when everything is quiet. I have not been subject to any loud noises or any colds or sicknesses. This has been going on for four weeks. Could it be related to my being pregnant, or the fact that I am now taking a prenatal vitamin with iron (150mg)? -- D.S., Baton Rouge, Louisiana

DEAR D.S.: Ringing in the ears, also called tinnitus (tih-NY-tuss), can represent a wide spectrum of phantom sounds brought about by a variety of conditions. It is often accompanied by hearing loss. I am familiar with tinnitus, as it remains a most unwelcome visitor in my own life. Hopefully yours is temporary, so let's take a brief look at the buzz on this annoying condition.

Normally, external sound vibrations strike the eardrum, causing the bones of the inner ear to vibrate and conduct the sound to the acoustic nerve. The (mechanical) acoustic vibration gets translated into an electric nerve signal, which then travels to the brain for interpretation. With tinnitus, something inside the head causes the acoustic nerve to fire. This "something" might be an inflammation, infection, blockages, malfunctions with the inner ear, otosclerosis (an overgrowth of the inner ear bones), pressure from abnormal tissue, a blood pressure issue, anemia, an allergy, a reaction to a medication (even something as common as an OTC pain reliever), a cumulative effect of exposure to loud noise, or the actions of a toxic agent.

As you can see, it is a long list.

There is an increased prevalence of tinnitus during pregnancy, which could indicate that your symptoms are temporary. I think it would be in your best interest to mention this to your physician or obstetrician, and possibly to have it checked out by an ear specialist. An expert can help you better understand what is going on, and rule out any possible situation that could be of concern during your pregnancy. In addition, there may be some intervention that could help prevent matters from getting worse.

Check out the fact sheet and article on tinnitus from the U.S National Library of Medicine: tinyurl.com/ztvu2pu and tinyurl.com/hwrdxok.

DEAR DR. BLONZ: I wanted to report a reaction my daughter had to rose-hip tea, as I know rose hips are ingredients in many vitamin C products.

In her late teens, my daughter was covered with hives within an hour of drinking some rose-hip tea. I rushed her to the nearest doctor, who informed me that the hives, which were even in her throat, could have caused suffocation, or even death, had she been brought in even one hour later. -- M.D., Chicago

DEAR M.D.: I appreciate the importance of your note, and I trust that others will take heed to the lesson learned by you and your daughter. Your story is a reminder about the potential dangers of food allergies, and it counsels alertness and caution when trying new foods. Any untoward reaction -- especially one that can affect breathing or blood pressure -- is not to be trifled with, and medical attention should be sought immediately. Read more on allergic reactions at: tinyurl.com/ne3g6zl.

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.