DEAR DR. BLONZ: I drink decaffeinated coffee, but have been hearing about dangers from the methods used to remove the caffeine. Is organic decaf any safer? -- S.A., San Diego

DEAR S.A.: To make decaf coffee, you want to remove caffeine while leaving all other substances in place. This requires the use of a caffeine solvent and specialized methods. Solvents currently in use include water, methylene chloride, ethyl acetate, triglycerides or pressurized carbon dioxide.

One “indirect” method involves taking a load of green coffee beans and placing them in a quantity of water. All water-soluble substances, including caffeine, are drawn into the water. This solution is separated from the coffee beans, and that first batch of beans is discarded. The next step is a process that selectively removes the caffeine from the solution. This can be done using a different solvent that is subsequently eliminated, along with its caffeine, or by passing the caffeine-rich water extract through a specially treated charcoal filter that grabs only the caffeine. The latter process is referred to as the Swiss Water Process. What’s left is a working solution containing all water-soluble components, minus caffeine.

The next batch of green coffee beans gets put into the working solution. Only caffeine gets extracted, because an equilibrium exists between the concentration of the other water-soluble components in the beans and that which is present in the working solution. The decaffeinated second batch moves on to get roasted, and that second solution goes through its caffeine-extraction step to be used with subsequent batches.

A “direct” method involves mixing the selected caffeine solvent directly with the beans. Methylene chloride or ethyl acetate are the solvents most often used. After it has had a chance to dissolve the caffeine, the solvent is removed, with the caffeine in tow. The beans are gently steamed to eliminate any remaining solvent residue.

Methylene chloride is a carcinogen, but there shouldn’t be any left on the beans to pose a health risk. This is because methylene chloride evaporates around 110 degrees -- well below steaming temperature, and also well below the temperature at which coffee is brewed. Ethyl acetate is a compound that naturally occurs in fruits and vegetables, and is often used when decaffeinating tea leaves. In all the above, the green coffee beans (or tea leaves) are ready for drying, roasting or further processing after the caffeine is removed.

Other, more expensive methods utilize carbon dioxide that has been liquefied under high pressure. (This is a process approved for organic coffee and tea production.) The liquefied CO2 dissolves the caffeine from the tea leaves or coffee beans and is then drained off. Another method utilizes the fatty substances called triglycerides.

Whatever the method, decaffeination technology has improved greatly over the years, and flavor differences are often hard to detect. Much also depends on the quality of the beans and tea leaves, together with the particular practices of the roaster.

Note that the use of the term “water process” with decaffeinated beans doesn’t tell you the whole story, since most indirect methods utilize a water extraction somewhere along the way. If the label specifically states “Swiss Water Process” or has other additional information, a better determination can be made. There is more on this topic at tinyurl.com/gov9l88.

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 have been eating vegetarian for over a year now, and I keep reading about compounds in vegetables that prevent minerals from being absorbed. I’m concerned, because my main sources of calcium are vegetables and grains. -- G.R., Portland, Oregon

DEAR G.R.: Some vegetables do contain compounds that bind, or “chelate” (KEY-late), minerals such as calcium, magnesium, iron and zinc, preventing their absorption. Two examples of these compounds are phytates, found in oatmeal and other whole grains, and oxalates, found in rhubarb and spinach (among other foods).

Spinach, for example, appears to be a good source of calcium and magnesium: A 100-gram (3 1/2-ounce) serving has 99 mg of calcium (10 percent of the Daily Value) and 79 mg of magnesium (20 percent of the Daily Value). However, by virtue of its oxalate content, spinach should not be considered a good dietary source of these minerals.

Usually, about 10 to 25 percent of the calcium in foods tends to be absorbed, but a study in the April 1988 American Journal of Clinical Nutrition reported that only about 5 percent of the calcium in spinach is actually absorbed. A second study two years later in the same journal reported that the calcium absorption in a low-oxalate vegetable, such as kale, was comparable to that of dairy products. It is important to appreciate that spinach is a wonderful food and a rich source of phytonutrients, aside from any impact of oxalates on the bioavailability of its minerals.

An interesting story along these lines relates to zinc deficiency, which was first described in men consuming a high-phytate cereal-grain diet. The phytates in whole grains are not a problem in yeast-leavened breads: Enzymes in yeast can break the bond between the phytate and the mineral, making the mineral bioavailable. With pita bread and similar items, however, which undergo a relatively short fermentation and baking, there isn’t sufficient time for the yeast enzyme to work its magic. As such, zinc deficiency tends to be more prevalent in parts of the Middle East where pita bread can account for as much as 85 percent of calories. Zinc deficiency has a number of effects, one of which is stunted growth if present during childhood. For more on zinc, see tinyurl.com/owql53a.

Seeing as vegetables and grains are the core of your diet, make sure you include a variety of different food sources. Fruit and vegetable sources of calcium without significant quantities of chelators include broccoli, turnip greens, collards, kale, mustard, figs and almonds.

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 enjoy making tuna salad sandwiches, but wanted to know about the different types of tuna. Does canned tuna packed in oil have higher levels of omega-3 fat than tuna packed in water? -- M.M., Hayward, California

DEAR M.M.: With few exceptions, the oil used for canned tuna is either soybean or canola oil, not fish oil. As a result, the oil-pack contains extra fat, but little in the way of extra amounts of the healthful omega-3 fats. A 3.5-ounce serving of light tuna in water (drained) contains 0.8 grams of fat and 0.3 grams of omega-3 fats. Contrast this with light tuna in oil (drained), which contains 8.2 grams of fat and 0.2 grams of omega-3 fats.

For more of the omega-3 fats, consider using the albacore (white) tuna. A 3.5-ounce serving of water-packed albacore contains about 3 grams of fat, of which 1 gram is omega-3. This is due to the fact that light tuna is made from the yellowfin and skipjack varieties, and these contain less of the omega-3 fatty acids than albacore.

For more issues relating to tuna, including a brief discussion of mercury, sodium and ecological concerns relating to how the fish are caught, check out the article at goo.gl/RyzX8u.

DEAR DR. BLONZ: I am all about avoiding partially hydrogenated oils and trans fats, but what about “fractionated vegetable oils”? What does “fractionated” mean? I’ve come across the ingredient several times, most recently in a “soy chocolate peanut” protein bar. -- L.S., San Diego

DEAR L.S.: Fractionation is a process by which fats and oils are separated into various fractions, often based on melting characteristics. It is a preferable alternative to partial hydrogenation because it does not lead to the formation of trans fatty acids. One example of the use of fractionated vegetable oil might be as an ingredient in a coating or frosting. In this case, manufacturers have an interest in selecting the “fraction” of the oil that works best to help the product remain solid at room temperature.

DEAR DR. BLONZ: I have been taking Coumadin for about a year now, as prescribed by a Kaiser clinic. I recently had an episode of internal bleeding and needed surgery. I am recovering, and they want me to begin taking the Coumadin again. To your knowledge, are there any studies that differentiate Coumadin from other blood thinners? Are there any natural dietary supplements I might take to act as blood-thinner agents? -- K., Richmond, California

DEAR K.: As I am not a medical doctor, I cannot offer medical advice, and that is what you need. The health professionals at Kaiser should be able to discuss the advantages/disadvantages of various anticoagulant medications. I would strongly advise against any reliance on dietary supplements for this purpose. That being said, it is essential that you inform your health care team of any dietary supplements you take.

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.