DEAR DR. BLONZ: Most fresh potatoes are not sold right out of the field, but are stored first -- sometimes for many months. Do they lose their nutritional value in storage? -- S.G., via email

DEAR S.G.: Fresh tends to be best, but if stored under proper conditions, potatoes do quite well with little nutrient loss. Cool, dry and dark conditions are the key, with “cool” defined as a range of 45-50 degrees F. Exposure to warmth or light will cause the potato to come out of its dormancy, begin to sprout and take on a greenish tinge. Potato sprouts or green parts are NOT to be eaten.

If stored correctly, mature potatoes will keep well for up to two months. Aside from their carbohydrate content, an average-sized potato (with skin) is a good source of vitamin C and potassium, and also provides a couple of grams of fiber, several B vitamins, magnesium, iron, phosphorous and zinc.

DEAR DR. BLONZ: My reading of food ingredient labels often reveals “modified food starches” somewhere on the list. I prefer to make foods from scratch, but this is not always possible. Are these ingredients I need to be concerned about? -- W.H., Charleston, North Carolina

DEAR W.H.: A modified food starch is a complex carbohydrate that has been chemically modified to change some of its qualities. These would include texture, the ease with which the starch dissolves, and how readily the starch can be digested. Modified food starches are used in processed foods as thickeners, as formulation aids (to help maintain a desired consistency or texture), as an anti-caking agent (to help keep powdered foods free-flowing), or as a humectant (an additive that absorbs and maintains a food’s water content). Typical foods that contain modified starches include sauces, pie fillings and gravies.

Modified food starches are usually synthesized from a naturally occurring food starch, and they are not considered to represent a health risk. Those sensitive to gluten, however, should avoid foods containing modified food starches unless specifically labeled as “gluten-free,” as the starch may have originally come from wheat or another gluten-containing grain.

DEAR DR. BLONZ: My son and son-in-law both suffer from kidney stones. Can you tell me what foods they should not eat? -- A.T., Phoenix

DEAR A.T.: Kidney stones are among the most painful conditions that people can have, and they can develop for a number of reasons. There are different types, so an essential first step is for each of your relatives to work with his physician to determine the type of stones he has, and what might be responsible for them. Don’t wait; find out what is going on. Once you have this information, there will be more specific steps to take. The therapy will depend on the type of stone being formed. About the only common advice is to drink plenty of water.

There is more information on kidney stones at the National Kidney and Urologic Diseases Information Clearinghouse: kidney.niddk.nih.gov

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: When cooking beans, will adding ginger to the water reduce the amount of intestinal gas from eating them? Where does the gas come from? If using this technique, how much ginger would be needed for 1 lb. of beans? And should I use fresh ginger or ground, which also affects the amounts? -- S.K., Las Vegas

DEAR S.K.: Beans contain particular carbohydrates called oligosaccharides. The body does a poor job of digesting these, because we don’t produce sufficient amounts of the particular enzyme required to do that job. As a result, these carbohydrates travel through the small intestine undigested, then arrive in the large intestine, where they serve as sustenance to the natural flora that live there. Flora can give off methane and other gases as a metabolic byproduct of their meal. Some of the intestinal gases get absorbed through the intestinal wall, but when production exceeds this ability, the excess gets passed out of the body. All this will vary from individual to individual.

I am familiar with ginger’s reputation of being able to reduce the gas from beans. There is, however, little available in the scientific literature that describes how this herbal root might accomplish the task. Some of the information says that ginger works its wonders when you add it to the soaking water, as you mention above. I could not, however, find any guide that specified amounts or types of ginger.

What is confusing is that there are other articles saying that the anti-gas effect comes when you use ginger as a seasoning with already-cooked beans. One article even made reference to “research in India,” but again, there was little to be found in the scientific literature. On top of all this, we have ginger’s reputation as a digestive aid unrelated to beans, as well as its recommended use to help with various forms of nausea, including morning sickness and post-surgical nausea.

Aside from giving ginger a try, there are other techniques that can help limit the impact of gas production. One is to eat more slowly, chewing foods thoroughly, and enjoying beans as a part of a meal that contains protein and fat -- ideally preceding the beans. This helps because it slows the rate at which the food travels through the digestive tract, in turn slowing the rate at which the gas is produced.

Another option is to take an over-the-counter product that provides some of the missing digestive enzyme. The way the beans are cooked is also a factor. For more on this, see tinyurl.com/yb65zrzz.

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: I want an explanation for the post-meal sensation of tiredness long associated with Thanksgiving. Is it the turkey, or isn’t it? Last year, we had a hearty mealtime discussion about this, with a humorous footnote of all of us sitting around exhausted after the meal. But a number of us only had vegetarian dishes. This year, I wanted to go armed with some facts. What do you say? -- M.Q., Tucson, Arizona

DEAR M.Q.: Turkey does not contain any sleep-inducing chemicals; the connection between Thanksgiving and tiredness relates more to the nature of the feast. It all comes down to the size and makeup of the meal: The greater the amount of protein, fat and carbohydrate consumed, the more pronounced the soporific effect.

Survival equates with sustenance. So as foods are eaten, the body’s priorities shift, and blood flow gets shunted toward the organs that play a role in digestion and absorption. During mealtime, the brain makes shifts in its neurotransmitter controller substances. The body has its own home-brewed relaxation cocktail that encourages us to sit back, relax, and facilitate our ability to take it all in.

And assuming the Thanksgiving feast is your evening meal, all this takes place near the end of the day, when our energy is already on the wane. It’s a perfect scene for post-meal tiredness.

By the time the feast has finished, some of the component parts of the appetizers and the first of the other digested foods will have begun to enter the bloodstream: the great highway by which newly digested nutrients find their way to where they are needed. Carbohydrates break down to simple sugars and cause a release of insulin, the “I am fed” hormone that signals the availability of energy resources in the blood while keeping the blood sugar level from rising too high. Another of insulin’s effects is to encourage the amino acids liberated from the meal’s protein to enter cells to help with repairs or to build new tissue where needed.

Our bloodstream does not flow into the central nervous system, where the brain resides. Our brain is protected by a blood-brain barrier that controls the nature and amount of substances allowed in. Amino acids compete with each other to gain access. Tryptophan, one of the essential amino acids, was thought to be a key player in the turkey-tiredness connection. This makes intuitive sense because, once in the brain, tryptophan can be converted to serotonin -- a neurotransmitter that can elicit relaxation and calmness. Tryptophan is also associated with the production of melatonin, a hormone connected with sleep.

Turkey is a complete protein, and it does indeed contain tryptophan (though not significantly more than other complete proteins). But tryptophan must get to the brain to make you tired, and it is at a disadvantage because it’s found in smaller amounts than other amino acids in most foods. Carbohydrates tilt the odds through their stimulation of insulin, which causes many amino acids to enter other tissue. Tryptophan is less affected by insulin, and, its competition reduced, is better able to enter the brain and have its effect.

The tiredness you feel is due more to the overall volume and types of foods eaten at Thanksgiving. In particular, it’s the carbohydrate foods such as stuffing, candied yams, cranberries or dessert that lead to the fatigued feeling. If you were to have some other meat as the centerpiece, or even have a vegan Thanksgiving feast, the effects would be the same.

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.