DEAR DR. BLONZ: Please explain tryptophan's role in foods, and the reason it is being promoted as a separate dietary supplement called 5-HTP. -- C.L., Phoenix

DEAR C.L.: 5-HTP stands for 5-hydroxytryptophan. The key part of this compound is tryptophan, an essential amino acid and one of the building blocks of any complete protein.

During digestion, proteins routinely get broken down into their amino acid constituent parts. This is a necessary step before absorption, because intact proteins are too large to pass through the absorptive surface. After absorption, amino acids become available to participate in a number of biochemical functions, including being used to make new proteins or serve as building blocks for other substances needed by the body at the moment.

The first stop after absorption is the liver: our body's great processing plant. The liver plays a key role in the metabolism of proteins, fats and carbohydrates, as well as detoxification and biosynthesis. Think of the liver as having a grand conceptual "to do" list: changing and directing substances toward their new assignments, or packaging and labeling them for elimination from the body.

When tryptophan enters the liver, one option is for it to be made into a key neurotransmitter (brain chemical) called serotonin, which, among other things, encourages relaxation. When the body is unable to sustain needed levels of serotonin, a number of problems can develop, including depression and insomnia. Indeed, many antidepressant medications are specifically designed to maintain levels of serotonin in the brain.

5-HTP is an intermediary substance along the pathway by which serotonin is made from tryptophan. 5-HTP is normally converted to serotonin in the brain and, once made, it is unable to cross the blood-brain barrier and circulate in the rest of the body. However, when 5-HTP is taken as a dietary supplement, serotonin can be produced outside the brain, which might contribute to unwanted side effects. Safety concerns for 5-HTP include drowsiness, gastrointestinal distress and muscle problems.

Another issue is the risk of spasms of the coronary blood vessels that might increase the risk of a heart attack. Anyone at risk for coronary heart disease, and those taking antidepressants, anti-anxiety drugs (SSRIs) or MAO-inhibitor medications, should be sure to check with their physician before considering this substance. (See https://goo.gl/s2Jdda for a summary of typical uses and concerns regarding 5-HTP.)

There is research evidence attesting to the potential benefits from 5-HTP in specific circumstances, but there are also concerns, as listed above. You make no mention of why you are interested in this substance, and that makes it difficult to say whether current research supports your intended use.

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: 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.