DEAR DR. BLONZ: I have been reading about our bodies' need for enzymes. While the companies selling enzyme supplements certainly have an interest in promoting their importance, I'm concerned that there is something to their claims. Does cooking really destroy enzymes, and do we stop producing them as we age? -- E.I., Oakland, California

DEAR E.I.: A defining characteristic of an enzyme is that it effects change in another substance while remaining unchanged itself. The enzymes in our body are specialized proteins that not only help us make use of the energy in foods, but also play a role in the building and taking apart of complex substances.

There are situations where it might be reasonable to take an enzyme supplement. For example: Many adults no longer produce a sufficient amount of lactase, the enzyme that breaks down the lactose carbohydrate found in milk. The symptoms of "lactose intolerance" can include intestinal gas, cramping and diarrhea. Taking lactase supplements with milk products can reduce the annoying side effects. Another popular enzyme supplement (Beano) is based on alpha-galactosidase, an enzyme that helps digest a type of carbohydrate found in beans and some other vegetables.

There are also medical situations in which dietary enzymes might be prescribed. The pancreas produces many of our digestive enzymes. If a medical problem develops that affects the pancreas's ability to either produce or deliver its enzymes to the digestive tract, the body will be unable to digest and absorb a variety of essential nutrients.

Problems with enzymes can also be experienced by those who have undergone a gastric bypass. Those with such issues would have a legitimate reason to take specialized enzyme supplements.

But what about those who don't have an enzyme-related malady?

There is an unsubstantiated theory that our lifespan is closely intertwined with our ability to produce enzymes. It is based on the dubious idea that we can only manufacture a fixed amount of enzymes in our life; when we run out, the game, so to speak, is over. The theory posits that fresh fruits and vegetables contain "live enzymes." By eating a diet rich in raw, whole foods (because cooking kills the enzymes, they say), or by taking enzyme supplements, we effectively spare the "drain" on our bodies' resources and help extend our lives.

There is no foundation for this enzyme theory, especially the part about the body having a fixed amount of enzymes. Fresh foods are healthful not because they contain enzymes, but because they are our richest source of nutrients and phytochemical substances. Given that enzymes are protein substances, those in foods will be inactivated in the stomach's acid environment and disassembled by the protein-digesting enzymes in our digestive tract.

By all means, eat and enjoy fresh, whole plant foods -- but don't hold them in any special esteem for their enzymatic powers.

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: Our school year is now underway, and I am again being pressured by my sons to include too-sugary snacks in their lunch boxes. I have volunteered in the lunchroom, and have noticed that those who don't get what they want tend to trade items with their classmates. My boys are 8 and 10, are active and usually eat well. I try to only buy snacks that claim to be made with fruit, but I am skeptical of their nutrition. -- F.K., Los Angeles

DEAR F.K.: The idea of the lunchtime snack represents a gold mine for food manufacturers, and your plight is by no means unique. All one needs to do is check the advertisements in magazines, the commercials during kids' TV shows, the ever-present online ads and the kids-eye-level shelves at the supermarket. Although there have been some changes, most "fruit snack" and "fruit roll" products still offer little more than a sweet taste and a lot of packaging. Many are just pseudo-fruit doodads aimed at the young consumer.

The manufacturers' goal is to cajole parents into choosing their products as a convenient way to add fruit to their children's diet. Though the packages boast that they are "made with real fruit," they're usually nothing more than gummy sugar concoctions with little more than a hint of the genuine article. Check the Nutrition Facts label and the ingredients list to compare the amount of added sugar to actual fruit.

A better way to add good taste and nutritional value to the lunch box is to pack real, dried fruits. There are many options in that category, too, so choose ones with the least amount of added sugar (if any). These will offer the sweetness kids seek, but with more varied flavors -- not to mention, much more impressive nutritional content.

For example, delicious dried blueberries contain 10 grams of fiber per half-cup serving; figs and dates contain nine grams; dried apricots, eight; prunes, seven; and raisins, five grams of fiber per serving. By comparison, a slice of whole-wheat bread or a half-cup of broccoli each have about two grams of dietary fiber. (The typical American consumes about 12 grams of dietary fiber each day -- far short of the recommended 25 to 30 grams.)

In addition to fiber, dried fruits are good sources of B vitamins and other nutrients. Figs are one of the richest nondairy sources of calcium: One serving of figs contains 144 milligrams of calcium, which is higher than milk on an ounce-by-ounce basis. Figs also are a good source of iron, vitamin B-6, magnesium and copper. Apricots are a standout because one serving provides one-fourth of the U.S. RDA for iron, and enough beta carotene to satisfy most of the daily value for vitamin A.

Nuts and seeds are also healthy snack options, and they go well with dried fruit. You can also try a few pretzels, low-fat chips or a bit of granola. I recommend working with your children to make their own personal trail mix -- a healthful combination individually tailored to each child's tastes.

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: The bread offerings at my market continue to expand with not only white and various types of wheat, but other grains and a variety of gluten-free options. I have no issues with gluten, but I remain confused about the relative nutritional merits of all these various bread types. -- B.L., Sun City, Arizona

DEAR B.L.: To better understand these breads, it will help to know a little about the wheat grain, or kernel. The kernel consists of the bran, the endosperm and the germ (tinyurl.com/qjbdk9f).

The bran is the protective outer shell of the grain, composed primarily of a nondigestible dietary fiber (bran) and a small amount of B vitamins. The endosperm, which is mostly starch (carbohydrate) with small amounts of protein, vitamins and minerals, is the central ingredient in the bread-making process. The germ is the embryo inside the grain; if the intact grain were to be planted, the germ would grow into a new plant. The germ contains most of wheat's vitamins and minerals, plus a small amount of essential oils: the nutrients needed by the wheat to fuel development until it can begin getting them from sun and soil. Because there are unsaturated oils in the germ, the wheat grain evolved to include vitamin E and other antioxidants to keep the fats from going rancid.

The internal contents of the grain are used to make bread. Cracked, crushed and whole-wheat flours all contain the entire wheat grain. In cracked wheat, the grains are cut in angular pieces; in crushed wheat, the grains get, well, crushed; and in whole-wheat flour, the entire grain is milled together. Each of these flours create breads of differing consistencies, but comparable nutritional value.

White flour, on the other hand, consists of the endosperm without the bran or wheat germ. Aside from the fact that it's a carbohydrate, it offers less in terms of native nutritional value. For this reason, white flours are usually enriched with added niacin, riboflavin, thiamin and iron to bring them up to the levels found in whole-wheat flour. Unless purposefully added, other naturally occurring wheat nutrients -- including magnesium, zinc, vitamin B6, vitamin E, folate and fiber -- are usually not present in white flour.

To find the healthiest bread options, you will have to read labels carefully. All flours made from the wheat grain can be called "wheat" flour, so it is perfectly legitimate for manufacturers to use the terms "white flour" and "wheat flour" interchangeably.

Don't be fooled by a bread's color: Some companies use white flour, legitimately call it wheat flour, but then add caramel coloring to make the bread appear to be whole-grain. On the flip side, whole-grain breads tend to be heavier in texture, so bread makers often add gluten to make it softer. Some do this by adding white flour, which has more gluten per unit weight, while others add pure gluten to the mix.

The healthiest products are the least refined and have the greatest percentage of whole grains. Look for "cracked," "crushed" or "whole-grain wheat" at the top of the ingredient list, regardless of how many different grains are used.

Whatever your choice, aim for a product that has at least one gram of fiber per slice. Make it a habit to check the Nutrition Facts panel and the list of ingredients when comparing products.

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.