DEAR DR. BLONZ: Can you explain for me and your other readers the difference between probiotics and prebiotics? Are foods and supplements containing these things beneficial? -- B.S., Walnut Creek, California

DEAR B.S.: There is a diverse colony of "friendly" bacteria that reside in our intestines -- mostly in the large intestine, also referred to as the colon. The scientific term for this colony of benevolent bugs is the "human microbiome." Consider this: There are more organisms in each of our microbiomes than there are cells in our bodies.

While our understanding of how these bacteria all work together and influence our well-being is in its relative infancy, it is now widely appreciated that the microbiome plays an important role in our general health. It is a fascinating and evolving field. (For a more in-depth discussion, check out tinyurl.com/gnlwgvg).

Probiotics are dietary sources of the specific bacteria in the microbiome. These can be found in cultured foods, such as yogurt and kefir, or in dietary supplements that contain levels of individual strains of bacteria. Typical organisms include specific strains of Lactobacillus, Saccharomyces, Bifidobacterium and Streptococcus. While there are major and minor players, each of us has our own symphony of microorganisms based on our diet, lifestyle, health status, genetics and even the medications and dietary supplements we use.

It should be appreciated that the microbiome is a "Wild West" situation with no sheriff -- the only law is survival of the fittest. So, too, is the current state of scientific affairs regarding how we might be able to adjust flora to accomplish specific health goals.

The potential for interpersonal variability makes it difficult to predict the effect of a particular probiotic, or combination of probiotic organisms, on any given individual. Then there are issues of effective dose and persistence. How much is needed, and how long does it have to be administered, for there to be a lasting effect with a particular individual's microbiome?

At present, we find probiotics being marketed to the general population claiming to accomplish health benefits. As we continue to gather evidence, researchers will gain a better understanding of the potential for probiotics to influence the microbiome, and effect changes in our health. Prudent consideration is advised in the meantime. Stick with advice from trained experts; if specific health problems are on the table, consult with physicians familiar with your particular health situation.

A prebiotic is a food that facilitates the growth and survival of the probiotic bacteria. These tend to be substances that are not effectively broken down by the human digestive system, allowing them to pass through to the large intestine where they serve as food sources for the flora. Dietary fibers, inulin, and oligosaccharides are substances that serve as prebiotics. They tend to be found in vegetables, whole grains and legumes, so a plant-based diet rich in whole foods will have a ready supply of nourishment for the friendly flora in your system.

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 begun taking statins for my elevated cholesterol. I've been advised to stop drinking grapefruit juice and eating grapefruit, because it impedes the body's ability to get rid of statins (and other medications). I enjoy grapefruit and am a bit disappointed, but certainly do not want to do anything to counteract a medication my body needs. Can you provide a brief explanation? -- S.T., San Jose, California

DEAR S.T.: Medications are given for a reason, but from the body's perspective, they are foreign substances that need to be eliminated. The body can rid itself of unwanted substances through the kidneys, the digestive tract, via breath exhalations, or even through the skin.

In many cases, medications or other "undesirable" compounds will first be broken down, or metabolized, by special enzymes prior to disposal. (Think of this as similar to the way that foods are taken apart by digestive enzymes before they can be absorbed.) The body uses various enzymes in its disposal system, but one of the stars is called cytochrome P-450 3A4, or CYP3A4 for short. This enzyme is present in the liver -- the organ that does the lion's share of the breakdown work. CYP3A4 is also present in the walls of our digestive tract.

The point of all this is that the partial breakdown of medication before absorption is normal and expected, as is the breakdown by the liver. These factors are all studied and accounted for when arriving at a drug's therapeutic dose. But grapefruit juice acts as a wild card because it inhibits the ability of the CYP3A4 enzyme to do its job. This is not an interaction with the medication itself; if that were the case, the effect would be more short-lived, persisting until the next dose. Rather, it is analogous to sand in the gears of an enzyme "machine."

This interaction was uncovered in 1989 when a researcher used grapefruit juice to mask flavors in a study designed to test how alcohol affected a particular medication. The results were unexpected, and the scientists soon realized that grapefruit was more than a benign flavorant. Researchers soon began investigating the range of the "grapefruit effect."

When grapefruit juice is around, more of the drugs get absorbed because the breakdown in the walls of the intestines no longer takes place. Grapefruit affects the ability of this enzyme to break down the medication, which means that blood levels remain higher for a longer period of time. Depending on the medication, the grapefruit effect can be serious, and it can remain long after the fruit is consumed. In one study, the effect was significant 24 hours after grapefruit juice was consumed.

Grapefruit and its juice cause this issue with a wide range of medications -- all those that are normally metabolized by the CYP3A4 system. The list includes some cholesterol-lowering drugs, certain anticonvulsants, calcium-channel blockers (prescribed for heart disease), cyclosporin (used after transplants) and benzodiazepines. If you enjoy grapefruit juice and you are on prescription medications, it is essential that you check with your pharmacist or your physician to see if your medication is at risk. Read more about the grapefruit effect at tinyurl.com/j4l72nf.

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 continue to read that we should not mix carbohydrates and proteins together. Is this the current thought among scientists? -- S.W., Portland, Oregon

DEAR S.W.: The idea that you should not mix carbohydrate foods with protein foods makes little scientific sense, and it runs contrary to the way the human digestive system is designed.

The foods we consume are systematically broken down until their component parts are suitable for absorption. It begins before any food is even consumed: Just thinking about eating and being exposed to the aromas, sights and sounds of food primes the digestive system for the meal to come. These sensory experiences, often referred to as the cephalic phase of digestion, stimulate the secretion of saliva (hence the term "mouth-watering"), along with other secretions important for digestion. Once some food has been eaten, the action of chewing keeps this going, while physically breaking apart the food from large to smaller pieces.

With the physical breakdown of the food come chemical treatments, featuring an enzyme in saliva and stomach acid designed to denature protein and break down complex compounds. Then comes exposure to a series of digestive enzymes, which are chemical compounds, each designed to disassemble a specific chemical bond holding protein, fats or carbohydrates together. This is all done in a sequential, "assembly line" arrangement; all digestible nutrients get attention before arriving in the areas of the small intestine where nutrients are absorbed.

The mixing of foods is not an issue at any stage of this process. Consider that many healthy, whole foods are combinations of protein, fats and carbohydrates. After you digest the above, I trust you will realize that this particular misinformation contains no "nutrients" you need to absorb.

DEAR DR. BLONZ: Why is palmitate an ingredient in powdered milk? -- M.L., Vancouver, British Columbia

DEAR M.L.: Palmitate is connected to palmitic acid, a saturated fatty acid. It is found in a number of foods, but the name comes from its primary source: palm oil.

Palmitic acid becomes "palmitate" when combined with another compound. In milk, vitamin A (or retinol) is combined with palmitic acid. The resulting compound can be called "vitamin A palmitate" or "retinol palmitate," or the milk product can list vitamin A and palmitate as separate ingredients. You can also see palmitate in other compounds, such as "ascorbyl palmitate," which is a combination of palmitic acid and vitamin C (ascorbic acid).

The amount of palmitate added to powdered milk is negligible. It is only there as an "escort" for the small amount of vitamin A added to the product. It helps to appreciate that palmitate is not a foreign substance to the human body: In fact, palmitic acid makes up about 25 percent of the fats found in breast milk. It's also present in human lung surfactant, a substance that coats the inside of our lung surfaces and allows us to breathe.

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.