DEAR DR. BLONZ: Is there an optimal form for a dietary supplement? Both my husband and I are over 60, and I was wondering if our bodies might better assimilate our daily vitamins and minerals from a capsule, tablet, gel cap, liquid or powder. -- S.I., Dallas

DEAR S.I.: "Food first" is the manta to be understood here. The overall quality of your diet is more important than the use of a product meant to "supplement" (not replace) what you eat. Once that concept has been digested and fully assimilated, the response to your question comes down to a matter of personal preference.

With few exceptions, taking supplements at mealtime makes sense, as there is all the churning and physical mixing of digesting a meal gives the vitamins ample opportunity to dissolve and be absorbed. I have heard that some people don't "trust" tablets because they feel they will pass through without dissolving, but reputable companies formulate their products to dissolve. If you have specific questions on that matter, put them to the company you are considering. Ask them to provide data on whether their pills, tablets, etc. will, in fact, dissolve when used as directed.

DEAR DR. BLONZ: My questions relate to caloric sweeteners. I read that fructose is sweeter than sucrose, so fewer grams of fructose are needed to achieve an equivalent sweet taste. Is this the case? What is the difference in sweetness between sugar, "invert" sugar, honey, agave and high-fructose corn syrup? -- K.E., Phoenix

DEAR K.E.: There are definite differences in the level of perceived sweetness between the various caloric sweeteners. Sucrose, or table sugar, is a double sugar, with each glucose bonded to a fructose. It gets broken apart during digestion by an enzyme. Sucrose serves as the sweetness standard, being assigned the relative sweetness value of 1.0. Fructose, also called fruit sugar, has a sweetness of 1.7, which means it is 70 percent sweeter than sucrose on a weight basis. So, when compared to sucrose, less fructose is needed to achieve an equivalent level of sweetness. The natural sweetness of fructose highlights one of the advantages of eating fresh fruits: You get plenty of sweetness per calorie, and you also get the other nutrients and phytochemicals found in the fruit.

Glucose by itself is less sweet than sucrose, having a relative sweetness of 0.7. Agave syrup has some glucose, but it is mostly fructose, so it will be sweeter than sucrose. Corn syrup is predominantly glucose; however, when being made into high-fructose corn syrup, a portion of it gets enzymatically changed into fructose. Invert sugar is sucrose that has been enzymatically split into its glucose and fructose components. It is similar to honey in that both are composed of equal parts glucose and fructose; however, with honey, those pieces are never linked together.

The similarity between invert sugar, honey, high-fructose corn syrup and sucrose is that they are all made up of glucose and fructose. The difference is that with all of these except sucrose, the glucose and fructose are not bound together. This affects the degree of sweetness, with the unbound glucose/fructose sweeteners having a relative sweetness of up to about 1.3, or 30 percent greater than that of sucrose.

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: 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.