DEAR DR. BLONZ: In a lecture at my community college, there was a statement that the turkey we have at Thanksgiving contains specific enzymes that make us feel sleepy after we eat. I had always thought that this was a myth, but was reluctant to challenge the professor. Is that statement valid? If so, what is in turkey that makes us feel sleepy after we eat it? -- M.M., Phoenix

DEAR M.M.: As a prelude to every holiday season, we hear the commonly held belief that turkey causes tiredness, but I had never heard it phrased as “specific enzymes.” Since this was an academic setting, you should not have been reluctant to ask more about these enzymes and how they supposedly cause tiredness. This is a new one, and I am always interested in learning the rationale behind such beliefs. I must confess, I am quite puzzled, given that the cooking of the turkey would destroy any enzymes in the meat.

Let’s put some other aspects of the turkey-tiredness legend in perspective. One key is tryptophan, one of the amino acid building blocks of protein. When this amino acid gets in the brain, it can be converted into serotonin, a compound that elicits relaxation and calmness. (One reason that a certain class of anti-anxiety drugs works is that it helps to maintain serotonin in the brain.) Turkey, as a complete protein, will indeed contain tryptophan, but it doesn’t contain that much more than other complete proteins, such as chicken or other meat.

Why, then, would turkey have the reputation for causing sleepiness, and not other proteins? It turns out that the tiredness you feel is more likely due to the carbohydrates often consumed along with turkey at the holiday feast.

To explain this, you should know that there is an important barrier between the blood that flows in the general circulation of the body and that which flows around the central nervous system. Called the blood-brain barrier, it helps protect the brain and control the compounds allowed to circulate in and around delicate brain tissues.

After a protein-based meal, the enzymes in our digestive system help break down the proteins into their constituent amino acids building blocks. Amino acids can pass through the blood-brain barrier, but they compete with each other to cross. Tryptophan is at a disadvantage because it’s found in smaller amounts in foods relative to other amino acids. Carbohydrates, however, can tilt the odds in tryptophan’s favor. Carbohydrates cause insulin to be released, and insulin causes amino acids to enter muscles and other body tissues, but tryptophan to a lesser extent. With its competition thus reduced, tryptophan is better able to enter the brain, turn into serotonin, and bring about the relaxation. 

Thanksgiving turkey tends to be paired with carbohydrate-rich foods such as cranberries, potatoes, stuffing and pumpkin pie, all of which raise our blood sugar level and ease the way for tryptophan to do its thing. Such logic would also explain why those who partake of other main courses -- such as ham, duck or even a vegetarian dish -- might feel that same post-feast tiredness.

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: What do you know about coral calcium? I was at a lecture where the speaker attributed anti-cancer properties to this so-called “unique” form of calcium. I just sat and shook my head, but was never given an opportunity to question the claims. I remain very suspicious, but wanted to ask you if there is any substance there. -- C.B. Seattle

DEAR C.B.: Coral calcium might be considered “unique” in that it comes from the structural matrix of ocean coral, but there is no evidence that it provides anything more significant or miraculous than “regular” calcium, an essential mineral nutrient.

The origins of coral calcium as a dietary supplement include an association with the long life of the people on the island of Okinawa. There have been unscientific statements about how these people’s intake of coral calcium has prevented or cured a veritable laundry list of diseases. There is also talk of coral calcium neutralizing toxic materials, and bringing the body into balance due to its alkaline (as opposed to acidic) nature. These statements are all sales pitch, and no evidence. A case brought by the Federal Trade Commission reflects these issues (tinyurl.com/m4t8d2y), but the products continue to be sold and the nonsense lives on.

Coral calcium is a type of calcium carbonate, the most common form of calcium supplements. And guess what? All forms of calcium carbonate are already alkaline. This is why it’s a common ingredient in many antacids. There is nothing special about the alkaline properties of coral calcium. As for the ability to “neutralize toxins” and cure or prevent disease, again, there is no evidence of efficacy.

As with all essential minerals, we need calcium. No surprise there. But there’s nothing miraculous about this particular type. You were right to be skeptical.

DEAR DR. BLONZ: What are the best food sources for niacin, thiamin and riboflavin, and what do these nutrients do? -- D.F., Charlotte, North Carolina

DEAR D.F.: All three of these B-vitamins are essential nutrients, ones that must be provided by the diet, as the body cannot produce them in sufficient quantities by itself. They are all involved in facilitating the release of energy, i.e., calories, stored in proteins, fats and carbohydrates.

Thiamin, also known as vitamin B1, is also required for normal functioning of the heart and nervous system. Food sources of thiamin include animal products (eggs, poultry, fish, meats and organ foods), whole grains, legumes, nuts, potatoes, and any food fortified with this vitamin. Niacin, also known as vitamin B3, is also required for normal cell metabolism and in the synthesis of hormones and DNA. Food sources include organ meats, poultry, seafood, nuts, green vegetables and legumes.

Riboflavin, also known as vitamin B2, is important for the health of the skin, the lining of the digestive system, and the lungs. Food sources include liver, enriched milk and milk products, meats, seafood, enriched grains, asparagus, broccoli, avocados, Brussels sprouts, eggs and green leafy vegetables. For more information on these and other vitamins, see medlineplus.gov/vitamins.html.

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: If oxidation starts when air hits the cut surfaces of foods, then shouldn’t one avoid all the produce items that come cut and ready to use? Such as pre-chopped celery, carrot sticks and sliced mushrooms? -- P.M., Pima, Arizona

DEAR P.M.: Consumers are demanding more fresh, natural and convenient foods, but it is important to consider that fresh fruits and vegetables are living tissues that continue to “breathe” and metabolize after harvest. While this does not imply a need to avoid ready-cut produce, we should have some basic understanding of the process so that we can be smart shoppers.

Plant cells contain many enzymes, some of which are tucked away in special locations in the cell, walled off from the rest of the cellular contents. They remain there “on assignment,” so to speak -- the plant relies on these enzymes to metabolize (break down) what gets brought in. The products of these enzymatic actions get released for use by the rest of the cells, and the plant in general. The housing of powerful breakdown enzymes in special sub-cellular locations keeps them from acting on the plant’s vital components.

When a plant food is sliced or peeled, or if the plant has aged and dehydrated, there can be a break in the protective subcellular membranes insulating the cellular contents from their own breakdown enzymes. The liberated enzymes can begin to act and initiate breakdown on whatever cellular contents they come in contact with. This causes an apple or banana to brown when cut or peeled.

Oxidation is another way that foods can break down, this often coming from a reaction with oxygen. Cutting or slicing does expose cut surfaces to air and oxygen, but the effects can vary according to the type of food and the way in which the food is cut, packaged and stored.

There can be slight changes in quality and nutrient losses, but these tend to be minor. Vegetables and fruits tend to contain their own antioxidants that can help stave off damage. It will be obvious if the damage is significant, as the food will be unattractive and unpalatable. Color and flavor components are vulnerable to the attacks.

Companies that make use of minimal types of processing often rely on low temperatures, special washes and oxygen-scavenging systems to slow breakdown. There is even “active packaging” and controlled atmospheres that can safely maintain product freshness.

Ready-to-eat products tend to be more expensive, but in exchange, you should get a wholesome, convenient food. Be sure to observe freshness dating, and let your eyes and nose be your guides to assure you are getting the best product.

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.