DEAR DR. BLONZ: Could you explain freezer burn, and whether foods that have suffered from it are safe to eat? I am particularly interested in whether it is safe to use freezer-burned foods such as beef, chicken or shrimp for soups or stews. -- S.T., Las Vegas

DEAR S.T.: Freezer burn describes the physical effect of a food losing moisture content from being in the freezer. In nature, there is a physical drive for substances in adjacent pools to mix and equilibrate. This even happens, albeit slower, at frozen temperatures.

In an attempt to equilibrate with the dry air of the freezer, the water content of a frozen food gets drawn to the surface and then pulled out. This involves sublimation: the process of a solid going directly to a vapor state without first passing through a liquid phase. Sublimation is integral to the freeze-drying process used with certain foods, but in the case of freezer burn, it is an undesirable side effect of frozen storage. This also explains why the ice in your ice cube tray shrinks over time.

The surface of an affected food will take on an “off” color and a leathery texture. Affected portions are safe to eat, but they won’t taste right. The formation and departure of the sharp-edged water/ice crystals are responsible for the rough texture in the “burned” foods.

The best way to protect against freezer burn is to pack your frozen foods in heavyweight, moisture-resistant wrap, such polyethylene freezer bags, aluminum foil, freezer film wraps or well-sealed plastic containers. Although they can hold liquids, standard plastic wraps can “breathe” a tiny bit, and that’s all it takes for moisture to escape in a dry, frozen environment. Brief uses of such wraps may be OK, but don’t trust them for longer than a week of freezer storage. Consider using plastic bags specifically labeled for freezer storage, since they have an additional barrier to prevent moisture loss.

You may, however, notice that even when using appropriate freezer containers or bags, some ice crystals will form in the non-food space during longer periods of storage. Do your best to make sure the bag or container is well sealed, with a minimum of dead space around the food. If you know it’s going to be there for a while, consider double-bagging.

Back to your issue: Depending on the degree of damage, you should be able to salvage these foods if you trim away the freezer-burned portions before cooking. If, as you say, all you want to do is to cut it up and use it in stocks, soups and stews, you may be able to salvage more, but I would proceed carefully to be sure you don’t have some undesirable textures in the final dish.

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 tuna, and have found a water-packed brand where the fish are caught in a way that provides a lower risk of contaminants. Does tuna packed in water still have high levels of omega-3 essential fatty acids? If it has less than tuna packed in oil, how much less? -- M.M., San Leandro, California

DEAR M.M.: The oil used for canned tuna is usually soy or canola oil, not fish oil (check the list of ingredients). As a result, oil-packed tuna contains extra fat, but little in the way of extra amounts of the healthful omega-3 fats. A typical can of light tuna in water (drained) contains 0.5 grams of fat and 111 milligrams of omega-3 fats. A can of light tuna in oil (drained) contains 8.1 grams of fat and 128 milligrams of omega-3 fats.

For higher levels of omega-3 fats, use albacore (white) tuna. One 3.5-ounce serving of water-packed albacore (drained) contains 2.5 grams of fat and 706 milligrams of omega-3 fats. The difference between “light” and “white” tuna stems from the fact that the yellowfin and skipjack varieties used to make light tuna contain fewer omega-3 fatty acids than albacore.

DEAR DR. BLONZ: I eat a variety of veggies, grains and legumes with my vegan diet, and beans are the biggest source of protein that I rely on. A close friend told me that fiber could hamper protein absorption, and I wanted your view on this. -- R.S., Martinez, California

DEAR R.S.: There can be a slight decrease in protein absorption on a high-fiber vegan diet, but this would only become an issue with a marginal protein intake. You have stated your interest in legumes; this means that having rice and other grains will make a complementary protein. Aside from this, there are lots of high-protein plant foods, such as soy and other legumes, along with nuts and seeds. All considered, it is doubtful that your fiber intake would be sufficient to cause problems.

DEAR DR. BLONZ: I read your article on protein for the elderly and want to add my sixpence worth of comment. A good source of protein is whey, as in whey powder. It is highly bioavailable and can be added to milk or yogurt or even in cooking. I read that whey protein is good not only for athletes, but also for the elderly and for people about to have surgery. -- M.N., Walnut Creek, California

DEAR M.N.: Thank you for that suggestion. Whey is a natural protein found in milk. It’s what’s left after milk is coagulated and the curd is removed. It may contain a small amount of lactose, that carbohydrate in dairy that many folks have trouble digesting. A pure whey protein isolate will contain only about 0.1 gram of lactose per tablespoon (20 grams of protein). This is the same amount of lactose that would be in one half-teaspoon of milk.

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: What could be in food that would make me itch? It is not particular to any one type of food, but now and then I have this strange itching reaction. It lasts for about a half-hour, and then it’s gone. -- D.I., Hayward, California

DEAR D.I.: A reaction to food is by no means the only factor that can make one itch, but allergies to certain foods or additives do occur, and skin reactions such as itching are a possible symptom.

There is a good overview of food allergies at the National Institutes of Health (tinyurl.com/yd7srkvd). The most common food allergies involve nuts, eggs, milk and soy-based foods, but theoretically one can be allergic to almost anything he or she eats. Food allergies are most often seen in children, with symptoms ranging from mild discomfort to a life-threatening anaphylactic shock.

It’s not always easy to identify the culprit, as a reaction can come from one factor or many. For example, one could get hives from a single food, a specific combination of foods, or a food eaten after taking certain medication. If you feel that you might be having a food-allergy reaction, but are unable to zero in on the particular ingredient or situation, it may be helpful to keep a diary of times and dates when reactions occur, along with the foods you had eaten. Over time, you might be able to identify the culprit. Don’t ignore what you drink, or any seasonings you’ve added to your food.

I recommend you bring this to the attention of your family physician for a couple of reasons. First, there are specific tests that can help identify an offending substance; more importantly, there may be factors in your health situation beyond food that need to be considered.

DEAR DR. BLONZ: My aunt and I have this ongoing argument. When I make an egg white omelet with sauteed vegetables for breakfast, tossing the yolk, I contend that I am making a more healthful breakfast. My aunt says the egg whites have little nutritional value and that all the good stuff is in the yolk. Who do you think is correct? -- R.S., Phoenix

DEAR R.S.: You both have your facts wrong. The whites of eggs are far from valueless; they contain a source of high-quality protein. In fact, egg white is the standard to which all other proteins are compared. There are approximately 3.5 grams of protein in the white of every large egg. There are small amounts of other nutrients, including selenium, potassium and sodium, but protein is the main contribution that the egg white provides.

The yolk, by contrast, contains lesser amounts of protein, together with small amounts of vitamin A, folate, phosphorous, potassium and selenium.

I am wondering why you are tossing your yolks. Is it because of their cholesterol content (213 milligrams in the yolk of a large egg)? For those with an otherwise balanced diet, the periodic use of whole eggs has been shown to have a minimal impact on blood cholesterol levels. You are throwing away good food.

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.