DEAR DR. BLONZ: I often see commercials for capsules of powdered greens and fruits and how they supply important nutrients and antioxidants, the same as eating whole fruits and vegetables. I have been taking this product daily for a few months and haven't noticed any effects. I want to know if these are a good replacement when I don't get enough fruits and vegetables in my diet. -- J.R., Oklahoma City

DEAR J.R.: I don't favor using supplements as a substitute for healthy eating. While these powdered products are made from dehydrated fruits and vegetables, there is no product standard, so you would have to check the ingredients list and label statements to see what's in each serving of a particular product. Some might be fortified with vitamins, minerals and phytochemicals, which must be listed on the ingredients statement. Outside of supporting testimonials, there tends to be little objective evidence available on these supplements. Look for studies that prove the products' efficacy.

Some supplements come in liquid form, some as tablets or capsules, and others come in powder form. They may have a grassy taste, but assuming you have no allergy or sensitivity issues -- which you should discuss with your health professional -- safety should not be a problem with products made according to the FDA's Current Good Manufacturing Practices (read more about these standards at b.link/uv7euav). However, relying on these supplements is not effective as a replacement for healthy eating. Taking care of yourself increases the odds that your body will be better able to fend off ill health and chronic ailments that are a part of the aging process.

To end this sermon, I suggest you reconsider your remedy for "not getting enough fruits and vegetables." The best thing to "take" is a plant-based, whole foods diet coupled with a healthy lifestyle. It's all a matter of priorities, and you will appreciate the payoff even more as you age. Healthful eating and an active lifestyle don't come with a guarantee, but they are the foundation of taking care of yourself.

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 received information from my doctor's office that read: "Don't take a multivitamin and mineral supplement containing iron. Men can't eliminate iron except through blood loss. High levels of iron in the body may promote cardiovascular disease/cancer." This information goes against the recommendation to take 8 mg of iron daily in my multivitamin. Please explain. -- R.A.

DEAR R.A.: Some context may help here. The human body has a daily requirement for iron, which it needs to make hemoglobin -- the oxygen-carrying compound in blood -- and myoglobin, a related compound that handles oxygen in the muscles. Both compounds are essential to producing energy for our cells. If the body has insufficient iron, the decreased hemoglobin and myoglobin levels can't produce needed energy.

The claim that men cannot eliminate iron is a bit confusing. The non-menstruating adult human body eliminates about 1 milligram of iron per day. Menstruating women lose significantly more. The daily iron requirement for premenopausal women (ages 18 to 50) is 18 mg. For adult men and postmenopausal women, the requirement is 8 mg a day. The dietary requirement is higher than the 1 milligram lost daily because we absorb only about 5% to 10% of the iron in our diet. Meat and poultry contain heme iron, which is the most efficiently absorbed form. (Read more on iron at b.link/z5msxnp.)

If you are an otherwise healthy individual with a healthful diet and lifestyle, you needn't fear taking a supplement that provides up to the recommended daily amount of iron, especially if the supplement is your primary source. There is no advantage, however -- and possible negative reaction -- in consuming excess iron. Discussing your multivitamin with a health professional familiar with your health issues is your best course of action.

Iron's darker side comes from epidemiological studies that found elevated iron stores associated with cardiovascular abnormalities and cancer. Consider how an iron nail will rust if left exposed to the elements, which is the result of iron's reaction with oxygen. Our bodies don't get rusty, per se, but it is thought that iron in our body grabs on to oxygen and then forces it on nearby substances, such as fats or cholesterol. (Oxidized fats and cholesterol are considered the primary villains of disease.) Antioxidants, including vitamins C, E and A, can help prevent errant oxidation and risk of disease.

Another element of iron's "Jekyll and Hyde" personality relates to individuals born with a genetic iron storage disease called hemochromatosis. Also referred to as "iron overload disorder," hemochromatosis is the inability to rid excess iron, which continues to build up, wreaking havoc on systems throughout the body.

Many people are unaware that they have this condition until symptoms emerge. Treatment often involves periodic removals of some of the patient's blood. Hemochromatosis is diagnosed via blood tests and genetic testing. (For more on hemochromatosis, see b.link/v9ndrk2.)

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: We often use commercial fat-free salad dressings as an alternative to a simple olive oil and vinegar dressing. They taste fine, but my daughter asked about all the chemicals listed on the ingredients statement on the bottle. I was hoping you would tell me what xanthan gum and cellulose gel are and whether they are OK to consume regularly. -- F.F., Hayward, California

DEAR F.F.: To be successful in the marketplace, a nonfat salad dressing has to be able to perform just like oil and vinegar and bottled, fat-based salad dressings; namely, it must coat the leaves of the lettuce, provide a pleasing mouthfeel and provide a vehicle for flavors.

Xanthan gum and cellulose gel are used precisely for these reasons, and both of these components appear to be quite safe for regular use at the level found in foods.

Xanthan gum was developed by the USDA during a project to find new uses for surplus corn. It is made from a corn syrup specially fermented from cornstarch. Xanthan gum helps to thicken the texture of food, and has proven to be quite versatile. Aside from salad dressings, it is found in puddings, sauces, baked goods and desserts. It is also found in toothpaste. Because it is made from corn, xanthan gum should be avoided by those who are allergic to corn. Aside from that, there do not appear to be problems generally associated with its use.

Cellulose gum is made from the fibrous cell walls of plants; it also functions as a thickener and is found in dressings, ice cream and puddings.

DEAR DR. BLONZ: This summer's heat is softening fruits quickly, but I hesitate to refrigerate fruits such as tomatoes, peaches and melons for fear of losing flavor. Is this a misconception, and should I go ahead and refrigerate them? -- F.M., Linden, New Jersey

DEAR F.M.: Refrigeration can slow the growth of many microorganisms, but it can also affect the quality of some foods. Tomatoes, for example, should be stored at room temperature, preferably away from direct sunlight in an airy location with moderate humidity; under these conditions they should last about five or six days. Storing a tomato in the refrigerator may delay it from going moldy, but some of its flavor and texture will be destroyed. This is particularly an issue with flavorful homegrown tomatoes and tomatoes purchased at a farmer's market. The effect is less clear with store-bought tomatoes, as they might not have as much flavor to begin with as homegrown. Another variable is sellers storing their tomatoes in the cooler.

Peaches and melons can be stored in the refrigerator, but you should wait until they are at the level of ripeness you like. (For more information on the best way to store fruits and vegetables, see b.link/n74hq9t.)

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.