DEAR DR. BLONZ: There are many companies offering vitamin and mineral deficiency tests, claiming to let you know which supplements you need. They test blood, saliva, urine and hair samples, in addition to asking questions about lifestyle and symptoms. In theory, these tests might take the guesswork out of finding the supplements one needs. But do these services work? -- W.S., Phoenix

DEAR W.S.: I remain skeptical of the deficiency tests you describe. Granted, vitamins and minerals play an integral role in bodily systems. Laboratories can determine if there is enough of a nutrient by observing or measuring specific tissues or chemical reactions. Such tests, however, are only useful in helping to determine if there is a stark deficiency.

A blood test, for example, might measure the activity of a particular enzyme that depended on the presence of a particular nutrient. Another approach might be to check for the occurrence of a particular symptom or abnormal metabolic byproduct that only appears when a particular nutrient is in short supply. In both these cases, you would detect a deficiency, but nutrient deficiencies of this type are uncommon. (Check tinyurl.com/jlz7unv for a report on the prevalence of nutrient deficiencies.) This is not the same as a test that can give you advice on the best vitamin and mineral regimen.

What about hair tests? In this approach, hair clippings are sent to a laboratory for analysis. The idea is that hair provides a running diary of our nutritional status at the time it was created inside the hair follicle. On the surface, this might seem to be a convenient procedure to provide useful clues to our inner workings. Hair analysis has been shown to be of value in uncovering certain toxicities, but it has never proven itself as a useful measure for determining an individual's unique dietary requirements. The same, unfortunately, can be said for saliva and urine tests.

The bottom line is that there isn't a precise way of determining an optimum intake level of any given nutrient for any given person. If anyone tells you otherwise, ask for evidence of their assertions.

DEAR DR. BLONZ: Are there certain B vitamins that stimulate the growth of fat cells? If so, which ones? -- N.K., Newark, New Jersey

DEAR N.K.: Fat cells, also called adipocytes, are distributed throughout the body, and they represent our energy reservoir. They grow in size as more fat, in the form of triglycerides, is dropped off for storage. Once they reach capacity, the body can make more fat cells. Once formed, fat cells are difficult to get rid of, remaining throughout our lives and changing only in the amount of fat they contain.

Fat cells, like all cells, depend on essential nutrients, but there is no evidence that B vitamins will stimulate fat cell growth, unless excess dietary energy continues to fill the existing fat cells. In that case, the issue is the intake of excess calories -- not vitamins.

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: Does putting milk in my tea (green, black or oolong) affect its antioxidant properties? I have seen and heard mixed answers on this topic. Please clarify it for me, as I do love milk in my tea. It would be very hard for me to stop this habit after so many years! -- T.L., Seattle

DEAR T.L.: First things first: Tea is a very healthy beverage choice. Population studies have suggested that compounds in tea can help reduce the risk of heart disease and other chronic ailments. Having at least one cup of tea per day, for example, has been associated with half the risk of developing a heart attack. This is thought to be due to the ability of certain compounds in tea to protect the fats in the blood (lipoproteins) from oxidation -- hence the term "antioxidants."

In relation to your question, the news is not all good, because a few studies have noted that the addition of milk seems to blunt the tea's antioxidant prowess. The final answers aren't all in, but the "milk effect" theory does seem to have some merit.

Take heart, and understand that tea is not the only antioxidant-rich substance available in our diets. As long as you have a healthful, plant-based diet overall, I encourage you to continue to enjoy your tea the way you like it. After all, eating and drinking should not always be viewed as a clinical prescription; enjoyment must have its place on the plate.

DEAR DR. BLONZ: Can soy products, such as soy milk, interfere with thyroid medication? -- R.S., Portland, Maine

DEAR R.S.: Yes, there is a valid concern here. The hormones produced by the thyroid gland regulate the metabolism in most cells of the body. Those who produce insufficient thyroid hormone are given medications that either stimulate greater production by the thyroid gland, or serve as a replacement for the hormone itself.

There is evidence that soy products can interact with the thyroid gland or its hormones, but not all soy products have the same effect. It doesn't appear that this would be a significant factor in adults eating soy as a part of a mixed diet. With thyroid medication, however, the story has an added level of complexity, because there can be a physical interaction that affects the absorption of the medication when soy is present at the same time.

It is always important to read the instructions and warnings for any medication you take. I say this because soy is not the only food with a potential interaction with thyroid medications. Many thyroid medications have specific instructions to be taken on an empty stomach to avoid potential interactions with foods. Be sure to consult your family physician, or a pharmacist, if you have any further questions.

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: At last year's annual physical, I learned that my triglycerides were over 400. Over the past year, I have been losing weight, and I also started medication for high blood pressure and high triglycerides. My levels are on the way down, but can you tell me exactly what triglycerides do in the body? -- T.L., Teaneck, New Jersey

DEAR T.L.: The role of triglycerides often confuses people. That's not surprising, given the speed with which many complex health terms have encroached upon our daily lives. The triglyceride can be thought of as the body's most concentrated package of stored energy. It is composed of three fatty acids attached to a 3-carbon (glycerol) structure, and can be a fat or an oil.

Fats and oils are usually differentiated by their states at 68 to 72 degrees F, the range referred to as "room temperature." Fats, such as butter or lard, will be solid at room temperature, while oils, such as olive, corn or canola oils, are liquid. (This definition has some wiggle room: Coconut oil, while solid at room temperature, has managed to cling to its "oil" name.) That being said, the term "fat" is generally used to refer to both the fats and oils in the foods we eat.

Triglycerides include the fats in our food, those traveling in our bloodstreams and those hanging around in the body's excess energy storage areas -- and we all know what that means.

We take in energy when we eat, after which our blood triglyceride level rises -- even if there's a limited amount of fat in the meal. This is because the body is programmed to avoid any waste of calories (energy), even if in the form of protein or carbohydrate. Excess energy will be converted into fatty acids by the liver, and then be packed into triglycerides and released into the bloodstream on its way to storage. Food fats are already in the form of triglycerides, but during digestion they are disassembled, only to be put back together after absorption. A high intake of alcohol or of sugars such as fructose, sucrose or glucose tends to increase the blood triglyceride level.

To get an accurate read on one's baseline triglyceride level, tests are usually given after a 12- to 14-hour fast. There can be lab-to-lab differences on what comprises a normal range for blood triglycerides, but generally speaking, levels above 200 milligrams per deciliter are considered high. You can read more about this at tinyurl.com/zps6kf5.

High triglycerides are now recognized as a risk factor for heart disease, which makes perfect sense when you think about it. Simply put, it is not in our best interest to have higher-than-normal levels of fats roaming around our bloodstreams. A high triglyceride level may be more of a risk factor if accompanied by an elevated blood cholesterol level.

Finally, let me offer my congratulations on your strides toward health. High triglycerides are more common in people who carry excess weight, so I wish you success in your continued efforts.

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.