DEAR DR. BLONZ: I do not eat much fish, and my doctor suggested taking fish oil capsules. My question is whether flaxseed oil is an effective alternative source of omega-3 fatty acids. This would be preferable to me, as it does not come with the risk of containing mercury or other contaminants, and there is no fishy smell. -- S.M., Phoenix

DEAR S.M.: Our body requires certain specially built fatty acids in the same way it requires vitamins, minerals and protein. Fatty acids are long chains of carbon atoms bound together. In chemistry, the term “omega” refers to the location of the first double bond along the chain. If it begins on the third carbon, it is called an omega-3 fatty acid. If it starts on the sixth, it’s an omega-6, and beginning at the ninth carbon, it’s an omega-9 fat. The precise point of that first double bond and the length of the chain affect what the substance can do in the body. We can make double bonds in some locations along a chain (such as at the omega-9 position), but not at carbon 3 or 6. We need fats built this way for various functions, and this is what makes omega-3 and omega-6 fatty acids dietary essentials.

Omega-6 fats are found in many vegetables, such as corn, soy, sunflower and safflower. The richest dietary source of omega-3 fatty acids is coldwater fish, such as salmon. There are also plant sources, and flaxseed is among the highest. Omega-3s can be found in lesser amounts in walnut, canola, soy and other plants, but these are shorter cousins to the ones found in fish oil, and it’s that longer version that the body requires for certain functions.

That means that while fish oil omega-3s are ready for the job, our bodies need to elongate plant omega-3s before using them. This can be done, but it is not an efficient process. Eating fish rich in omega-3 is definitely the best and most efficient way of getting these essential fats; the highest levels are found in salmon, tuna, mackerel, sardines and herring.

I consider fish oil capsules to be a lesser alternative. Concerns about contaminants are legitimate, so be sure to find a provider that goes the extra distance to assure the purity of the supplement before you buy.

Regardless of the source, omega-3 fatty acids must be stored properly as they are quite reactive. If they react with oxygen -- become oxidized -- they turn rancid and develop the odor characteristic of rotten fish. At that point, they change from an asset to a health liability. Refrigeration is ideal protection for these fats.

One final note: The intake of omega-3 fatty acids can affect how blood clots. Anyone using anticoagulant medications, such as Coumadin, or those at risk for issues involving blood clotting should get clearance from their health professional before starting or increasing their intake of omega-3 fatty acids.

For more information on omega-3 fatty acids from the National Institutes of Health, see b.link/EFAs.

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 the speed and convenience of cooking vegetables in the microwave, but became quite concerned when I read that this method might be destroying nutrients. Should I steam my vegetables instead of microwaving them? -- Q.T., Austin, Texas

DEAR Q.T.: It is reasonable to want the most from what we eat. Eating should be one of life’s great pleasures, and it makes no sense to sacrifice that enjoyment on the altar of requiring every last milligram of every nutrient.

Cooking can reduce the levels of certain nutrients, but it makes others more available for absorption. The answer to your question comes down to a matter of preference, and of using the technique with which you feel most comfortable.

The difference in nutrient composition after cooking is based primarily on the temperature and time of exposure. Microwaving is among the least destructive methods. Another issue is whether the food is submerged and cooked in water that then gets discarded; in this case, the cooking water can contain some of the water-soluble nutrients.

Steaming and microwaving are similar in both respects, so run with whichever you prefer. The most important factor is that you are eating and enjoying the bounty of fresh summer vegetables. Kudos on good eating habits, and their contribution to your health.

DEAR DR. BLONZ: Salt is a straightforward compound, so why does table salt need to contain additives? I know that they make salt iodized by adding a compound that contains iodine, but why are they adding other compounds such as calcium silicate and silicon dioxide? I have absolutely no problem with blood pressure, and use salt on occasion. Would I be better off using a natural salt or a sea salt where these compounds are not used? -- T.S., Sun City, Arizona

DEAR T.S.: Crystals of table salt are composed of sodium chloride, which can stick together when exposed to moisture in the room’s air. Salt that clumps together can have a hard time making it out of the shaker. One method to avoid this is to add dried rice or crackers to the shaker to absorb any moisture and keep things flowing. Another approach is to add very small amounts of compounds such as calcium silicate or silicon dioxide. (Silicon dioxide is the same compound in sand and quartz crystals.) These anti-caking substances are harmless at the levels used.

It is totally up to you: You can opt for a free-flowing product or one that needs more of a shake to be dispensed.

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: Sometime earlier in the year, I began adding a tablespoon of flaxseed to my morning granola. After about one week, I began to experience symptoms of vertigo. One day it was so bad that I could not even get out of bed in the morning. I have never experienced symptoms of vertigo before, so I thought it might be the flaxseed that was responsible. I stopped taking it, and the symptoms disappeared. Have you ever heard of such a case? -- F.D., Hayward, California

DEAR F.D.: Seeds are often sources of substances associated with food allergies, but reactions to flax are not common. Such an occurrence, however, is not out of the realm of possibility. The experience you relate certainly does cast suspicion in that direction. But your query highlights a situation we all must acknowledge: namely, that untoward reactions from foods do not always present with a clear connection between the cause and the effect.

When we experience something unexpected after eating, it is reasonable to consider the last thing consumed as a likely suspect, especially if it was something new. If it seems to recur whenever it’s eaten, we start to think we are on solid footing. What happens, however, if there is little basis for the connection, and our health professionals are unable to offer guidance?

If we are confident in our decision, we might act on our assumptions and cross the suspected offender off our “to eat” list. We might, however, be persuaded by the guidance of health professionals and begin to look elsewhere to explain the reaction. Or, we might simply chalk up the reaction as one of the many unexplained events experienced in life.

The bottom line here is that medical science is not always able to tell who will react to what. And while it may be a single substance you are reacting to, it may also be the dose that determines the reaction. For some, any amount of intake can cause problems, while others will only react if they take in more than their “threshold” of sensitivity. To further complicate the issue, there may be other foods or medications that change that threshold. Have a set amount of that certain food alone, no problem -- but have that same amount along with another food, or in a particular situation, and you experience the reaction.

There can be quite a detective game afoot, which is why it makes sense to keep a log of all foods consumed to help identify any patterns.

Research studies tend to say what is likely to happen to the “average” individual under a controlled set of circumstances. Such information can provide valuable insight, but regardless of what a study might tell you, we are all unique. Arm yourself with the required knowledge, then collect information about the reaction and the circumstances associated with its occurrence. Then, consult with a trusted health professional to exercise due diligence to chart the path forward.

Science is only as good as the latest study, so as new information and experiences become available, be prepared to reexamine your choices and make the appropriate changes. While it is essential to control items that make us ill, it is best to avoid dubious assumptions that continually shrink the circle of foods we can enjoy.

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.