DEAR DR. BLONZ: You have addressed the use of vinegar to help blunt the impact of carbohydrates on blood sugar levels. I want to know what white distilled vinegar is made from. And how is it made? Is it healthy or harmful? -- F.X., Los Angeles, California

DEAR F.X.: Vinegars are made from fermented carbohydrates and have been used as flavor enhancers, preservatives and folk remedies since 5000 B.C. There are many varieties, with their flavors depending on the type of carbohydrate used and other ingredients in the blend. (For a food-focused article on vinegar types, see b.link/Gqcapma.)

White distilled vinegar comes from the distillation of grains -- usually corn, but also rye and barley. The acid in vinegar is acetic acid, and it is usually present at about four parts per hundred (also expressed as 4% by volume). The main issue with using white distilled vinegar is that it has the strongest, most acidic taste of all the vinegars. It can be used in foods, but it is perhaps best suited for pickling. Vinegar does not provide any needed nutrients. While excess can overwhelm other flavors, vinegar is not unsafe or harmful when used appropriately.

DEAR DR. BLONZ: A friend told me how to figure out the percent of calories from fat. I am not a big math person, but I recall it was to multiply the grams of fat per serving by 9 (number of calories per gram of fat), then divide this amount by the calories per serving. I tried this on frozen hamburger meat that was 10% fat, but the calculation showed the fat was a whopping 52%. My confusion comes from my thinking that if it said 10% fat, only 10% of what you were eating was fat. -- M.S., Seattle, Washington

DEAR M.S.: Both your math and your friend's are correct. Ten percent of that meat is fat, but only if it's 10% of the weight. The confusion arises because the percent of calories from fat differs from the percent of fat by weight. We rely on the percent of calories from fat in dietary recommendations, where the totality of what's eaten is considered. With meat products regulated by the USDA, labels can declare the percent of fat by weight. (For more on foods under USDA jurisdiction, see b.link/p2y6f2c.)

You can calculate the percentage of calories from fat for an individual food by following your friend's instructions. There is a shorthand method for any food with a Nutrition Facts panel. Check the calories and grams of fat per serving. Every gram of fat per 100 calories equals 9% of calories from fat. So, if there are no more than 3 grams of fat for every 100 calories in a serving, the food derives no more than 27% of its calories from fat -- just below the recommended level. This method works regardless of serving size and is valid for both single items and meals.

When it comes to fats, the focus should remain on your entire diet. Almonds, for example, contain a variety of nutrients. If only percent calories from fat were looked at, you might be dissuaded from this healthful food when learning that 80% of its calories are from fat.

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: Are the natural flavors the same as what you would find in that actual food? For example, orange is one of my favorites; when a food labeled "all natural" says it is made with actual oranges but also lists "natural flavors" or "natural orange flavor" as an ingredient (I've seen both), is that referring to the oranges? -- M.R., Dover, Delaware

DEAR M.R.: Flavors come from collections of chemicals, whether made by nature or constructed in a lab. To copy the flavor from the naturally grown food for a processed food, flavor chemists identify nature's compounds at play. Precise, synthetic versions can be used to construct the desired flavor. The task, ironically, becomes more complex if the copy is to be a "natural" flavor. In that case, the compounds must come from natural sources such as fruits, vegetables, herbs, spices, meat, dairy or fermentation products, with no requirement that they come from the food whose flavor is being copied.

Why not use, or copy, the flavor substances in the actual food? While this seems preferable, it's impractical on any large scale. And, as flavors go, the natural ones are typically weaker when removed from their natural foods. Many are unstable and break down during processing, transport and storage. In addition, natural flavors may interact with other ingredients in a recipe, or even with the packaging material. There's also a question of uniformity. While fresh foods grown by nature can vary in flavor, processed foods must answer to a higher authority: the consumer. Biting into a less-sweet orange won't stop you from eating oranges, but an undesired taste in a processed food made with "natural orange flavor" might cross it off your shopping list for good. And, since opinions about taste vary, one company's version of a "natural" orange, or any other flavor, may taste nothing like another's.

Also consider that, from the plant's perspective, flavor is a short-term requirement, just long enough to get the fruit selected so its seeds can reach the soil. Energy is the most vital commodity; there is no need to invest more to keep flavors going when the energy priority is to fuel development until the plant can emerge, spread its leaves and begin getting energy from the sun on its own.

A good advertising campaign might persuade a consumer to try a product, but repeat business and ultimate success in the marketplace depend to a large extent on how it tastes. With today's demand and the level of expertise, we can no longer assume that a processed food product is more wholesome just because it uses natural flavors, or that it's inferior if the flavoring is artificial.

As for processed foods, always check the label to see what you are buying. While it may seem desirable to have "natural" or "nothing artificial" on the label, there's no automatic nutrition, taste or safety advantage that those with natural flavors hold over their synthetic counterparts. But, of course, we can avoid the flavoring issue altogether by sticking with fresh whole foods, which should be the main players in our diet.

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: Please explain more about placebos and controls and whether they can actually bring about health benefits. -- G.B., Anderson, South Carolina

DEAR G.B.: When early research results confounded expectations, scientists began to suspect that effects could occur simply because they were believed to be due -- even if no active ingredients were present in the treatment being given. (Key side note: And, yes, this may shed light on what's going on with "miraculous claim" supplement products that lack objective testing, but go heavy on product promotion. It is why potential customers should demand clinical evidence, rather than testimonials, before they buy.)

Scientists began using placebo controls in their studies to provide inactive treatments that appeared and tasted similar to the active treatments. When only the subjects do not know what treatment they are receiving, it is a "single-blind" study. However, many subjects wanted to know which group they were in, so they tried to pick up clues from anyone working on the research. Researchers often asked subjects at the end of the study whether they had learned which group they were in and how they had come to know it. When subjects have such knowledge, it thwarts the reliability of findings.

Quality researchers stepped in to design studies in which no one -- from the subjects, to those administering the treatments, to the researchers conducting the analyses -- could know who was in which group. Codes are used and are not broken until all the data has undergone final analyses. When placebos are used and nobody knows who's getting what, it's called a "double-blind, placebo-controlled" study, a premier method in clinical research.

An interesting side story was when an important concept was discovered using control treatments. In one study, grapefruit was used to mask the taste of a drug being tested so that subjects could not discern between the active treatment and the placebo. In this study, they found unusual results in the placebo group, revealing the profound impact grapefruit can have on drug absorption and metabolism. This finding led to our understanding and caution about the "grapefruit effect" with certain medications (see b.link/8mqcd for more).

DEAR DR. BLONZ: Is there any basis to the advice that the body shouldn't have fruits and vegetables at the same meal? Is this nothing more than a widely circulated, long-standing myth? If so, it dies hard. Thank you. -- A.S., Raleigh, North Carolina

DEAR A.S.: There is no one way of eating that works for everyone. We all have our quirks and preferences, food-prep abilities, social circumstances and takes on the physiological rules of the day. If there were to be a generalization in this matter, though, it would be that there is no evidence that fruits and vegetables have to be consumed separately.

Our digestive system is well-designed for mixed meals, having specific areas for the sequential breakdown, processing and absorption of the food's nutrients. The "die hard" aspect relates to period romances with misinformation from folklore that preceded evidence and our understanding of how things work in the body. For a more detailed view of our digestive system, see b.link/vq7rpkz.

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.