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.

DEAR DR. BLONZ: Please provide more information about the xanthan gum and cellulose gel that I find in my fat-free salad dressings. I tend to eat a lot of salad, and the dressings taste fine, but is there a reason to be concerned about eating these components on a regular basis? -- S.F., San Jose, California

DEAR S.F.: Dressing provides a flavor accent for the salad components, but to do this effectively, it must provide a light, easily distributed coating, and leave a pleasant mouth-feel. The two ingredients you mentioned serve these purposes in commercially produced dressing.

Xanthan gum is made from a specially fermented cornstarch syrup. It was created in the 1960s at the U.S. Department of Agriculture’s research station in Peoria, Illinois, as part of a project to find new uses for surplus corn. Xanthan gum helps to thicken foods’ texture and stabilize components in a mixture. It has proven to be quite versatile: Aside from salad dressings, it’s used in puddings, sauces, baked goods and desserts. Because it is made from corn, xanthan gum should be avoided by those who are allergic, but aside from that, there do not appear to be any problems associated with its use.

Cellulose gum is made from the fibrous cell walls of plants. It is a naturally occurring thickener used in dressings, ice creams and puddings.

Neither compound brings nutritional assets to the party, but they appear to be quite safe as food additives for use on a regular basis. Always read the rest of the ingredient list and the Nutrition Facts panel to see what else the product has to offer.

DEAR DR. BLONZ: I was surprised to see a dietary supplement proclaim oxygen as one of its active ingredients. How could that work? If it does, would it be a concern that effectiveness diminishes with prolonged use? -- H.B., Walnut Creek, California

DEAR H.B.: Let’s not get ahead of ourselves by assuming effectiveness. Oxygen is essential for carbon-based forms of life due to the many ways that carbon and oxygen can react together, and in the process, absorb or release energy. Oxygen is also involved in other metabolic processes.

The supplement angle makes little sense, as the body is designed to take in and utilize its needed oxygen via a gaseous exchange in the lungs, not as a dietary supplement that comes in through the stomach. This is not a route to deliver oxygen to the body. While there may be legitimate products out there, the Federal Trade Commission has gone after such dubious claims in the past (see tinyurl.com/q9k8cvr).

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.