DEAR DR. BLONZ: I hope you can clarify information about magnesium supplements on the market, including the hype that most are deficient, that it is a root cause of common ailments and the many promotional claims that their form "is the only one to get." -- H.N., Tulsa

DEAR H.N.: Magnesium, a major essential mineral in the body, is a key player in nerve transmission, the body's use of insulin and carbohydrate metabolism, muscle relaxation, normal heart rhythm, blood pressure regulation and overall cardiovascular health. The body needs magnesium to convert vitamin D to its active form, and, finally, magnesium is also needed for bones and teeth, with more than half found in our bones.

Plant-based, whole-food diets provide good amounts; sources include nuts, bananas, legumes, whole grains, avocados, dark leafy greens, milk and oysters. The recommended intake for magnesium is 420 mg per day.

Be aware that stated requirements take into account the efficiency of absorption. For example, if 30% of mineral compounds tend to be absorbed, a daily "requirement" of 1,000 mg would reflect that the body requires 300 mg (30% of 1,000) of that mineral.

You ask about the variety of magnesium supplements on the market; the essential concept is that whatever form it's in when swallowed, the magnesium that gets absorbed is all the same. Several forms compete for our attention, often promoted with exorbitant sales-talk claims. At issue is the ease with which magnesium separates from the compound it's bound to; that helps determine the amount of time the magnesium is in solution and available for absorption. Remember that a magnesium supplement consumed as part of a meal gains the advantage of the slower movement of the meal's bulk. In such cases, slight differences in solubility may not translate to meaningful differences in overall absorption.

As for magnesium's forms, oxide, sulfate and carbonate are less soluble; these do best if taken with a mixed meal. The more soluble forms include magnesium citrate, orotate, gluconate, aspartate, malate, lactate, chloride, taurate, l-threonate and glycinate (because glycine is an amino acid, this form gets referred to as "chelated" magnesium). Some products offer a variety of forms. Again, absent clinical evidence, do not be enticed by promotional claims of exorbitant superiority of one over the other.

Among the least soluble are magnesium oxide and magnesium hydroxide; the former has water-absorbing effects that can help soften hard stools and gets used in laxatives; the latter has acid-neutralizing abilities and is found in OTC antacids. These are not the best options to up your intake of magnesium.

The kidneys are critical to eliminating excess magnesium, so check with your health professional before taking supplements if you have renal issues. The important flip side is that when intakes fall below the recommended levels, the kidneys can help by limiting the amount lost in the urine. This tends to be the case with many nutrients, meaning there is no need to get frantic with occasional lower-than-recommended intakes. However, low magnesium intake for a long period can lead to magnesium deficiency. Those with gastrointestinal disorders, type 2 diabetes, or alcohol dependency issues, as well as older adults, can be at increased risk for magnesium deficiency.

It is best to be sure foods providing this essential mineral have a regular place in your diet; again, discuss the advisability of taking supplements with your health professional. Don't be swayed by overstated claims of clinical superiority of one soluble form over the other. I use "clinical superiority" in this advisory. While studies might show a few more milligrams absorbed of one soluble form of magnesium over another, this should not be assumed to impact the risk of disease (clinical significance). Getting the recommended amount of magnesium is the goal here. Check the National Institutes of Health magnesium fact sheet at b.link/979bks.

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: How long does it take calories in the foods we have eaten to become body fat? I have a physically demanding job, and I tend to gain weight during holidays when I am less active and tend to overeat. This seems to disappear once I return to work, along with better eating and activity. I am wondering at what point the excess fat becomes "permanent." -- D.M., San Jose, California

DEAR D.M.: Short-term body weight changes can be misleading and should not be assumed to parallel gains or losses in body fat. First, some background: Energy is the most essential commodity of life, and the body conserves and stores as much as it can, as body fat. While essential for survival as a species, this trait has an obvious downside if unchecked.

The calorie, a measure of heat, is the unit we use for the energy value of foods. Carbohydrates and protein provide about four calories per gram, while fats provide nine calories per gram. You mention holidays, so we must mention alcohol, which provides seven calories per gram. (For reference, there are about 14 grams of alcohol in a standard drink: 12 ounces of regular beer or five ounces of wine.) Like other animals, humans are designed to be mobile, so the body turns virtually all excess energy into fat, the most concentrated form.

One of my favorite examples is the plant world, where the priority is growth, not mobility. Plants evolved storing their energy as carbohydrates to get the most growth from their calories, helping them grow fast and spread their leaves to begin collecting energy from the sun. The exception for plants is their seeds, where mobility is again the priority. It explains why we find fat in seeds; this concentrated energy makes them light enough to be carried in the wind or by animals to a new destination with sufficient energy to fuel the growth of the new plant.

Your question is about immediate weight changes. There can be transient fluctuations in body weight due to shifts in body water, which can be affected by what you've been eating and drinking. Then there are unabsorbed materials in the queue for elimination, reflecting meal size and composition. Please enjoy your holidays, and don't fret short-term variances in numbers on the scale. Within a week or so, you'll see if things are there to stay.

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've been a coffee drinker for most of my adult life, but have now read that coffee absorbs calcium -- that it can even pull calcium out of bones and lead to osteoporosis. Is that true? And if so, does adding milk or half-and-half to coffee provide calcium to counter the effect and keep it from absorbing calcium elsewhere? I have osteopenia. -- S.T., Tulsa, Oklahoma

DEAR S.T.: Osteopenia is a "warning" state where bone mass is less than normal, but not as severe as osteoporosis. Our bones and skeletal system represent a cumulative record of our general and mineral nutrition and lifestyle. This structure can also be affected by genetic predispositions and medications that affect how bones get made and maintained.

Coffee is not a significant risk factor for osteoporosis in those who eat well. Caffeine doesn't actually "absorb" or "pull" the calcium out of the digestive tract or from your bones. Still, excessive intake can have a diuretic (urine-producing) property that can bring about a minor loss of certain nutrients, including calcium and magnesium. Coffee is also an acidic beverage, and it can irritate a sensitive stomach; having food with your coffee tends to buffer this effect.

Higher intake of caffeine coupled with inadequate calcium can be a risky combination. Eating well overall -- including a sufficient intake of dietary calcium -- counters this negative. The goal is a plant-based, whole-foods diet with adequate intakes of essential vitamins and minerals, including calcium. This will have more sway than adding milk or cream to the coffee cup. (One tablespoon of milk or half-and-half will contain only about 15 to 20 milligrams of calcium.)

In an example from the literature, a study in the American Journal of Clinical Nutrition affirmed that women who drink coffee during their postmenopausal years need to pay particular attention to the calcium in their diet. They found a link between an excessive intake of caffeine and an increased rate of bone loss. In this study, "excessive caffeine" was defined as greater than 450 milligrams of caffeine per day. (Note: Caffeine in coffee can vary according to the type of bean and the way it is brewed, but consider an average to be 100 milligrams of caffeine in a 5-ounce cup of drip-brewed coffee.) The study reported that the caffeine/bone-loss effect was not present in women having diets containing at least 800 milligrams of calcium per day.

Aside from caffeine, physical activity also contributes to the health of our bones, which can be said to have a "use it or lose it" aspect. Weight-bearing exercises such as walking, jogging, gymnastics or aerobics can help strengthen the bones -- no matter what age the activities are begun. Other nutrients -- such as magnesium; vitamins A, B6 and D; phosphorous; and fluoride -- are needed for calcium absorption and healthy bones. It's also important to avoid any habitual excess of dietary protein, as this can increase mineral losses.

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.