DEAR DR. BLONZ: Please provide some background about the use of chicken soup as a cold remedy. -- M.M., San Francisco

DEAR M.M.: Chicken soup has been used for generations, but a tradition can only go so far if it doesn't deliver. There is science here, but it will help to first understand what happens when you get a cold.

The immune system goes on the attack whenever it detects that a cold virus is attempting to take up residence in the upper respiratory system: the nose, sinuses and throat. A battle ensues, with one side effect being the inflammation that causes swelling of the mucous membranes lining the nose and throat.

At first, the immune system gets trounced, but over time, it learns to make the elements needed to squelch the invading virus. This can take hours, a few days, a week or longer, all depending on the tenacity of the virus and the state of your immune system. The "common cold" normally causes congestion, a runny nose, sore throat, a minor cough and a headache. If the virus persists and spreads down to the lungs, there is an increased risk of laryngitis (inflammation of the larynx/voice box), acute bronchitis and even pneumonia.

Stuffiness and discomfort are side effects, and they don't help the healing process. Congestion actually slows things down; if you rid yourself of the nasal secretions and mucus, you assist your immune system by allowing it to focus on making the weapons to win the battle. Blowing your nose is one obvious step, but care must be taken not to inadvertently force the bad stuff deeper into your sinuses (more info at tinyurl.com/pnfhjcn).

A group of physicians at Mount Sinai Hospital in Miami found that chicken soup was able to help clear the congestion that often accompanies a cold. This was discovered using a controlled experiment that measured the velocity with which mucus congestion was cleared through the nasal passageway. Dr. Irwin Ziment, a pulmonary specialist at the University of California at Los Angeles, attributed some of the soup's powers to the fact that chicken soup contains the amino acid cysteine, which is chemically similar to acetylcysteine, a prescription medicine used to combat congestion.

A cold is not the only instance where chicken soup can lend a hand: It can also help with asthma, where there is a narrowing in the bronchial tubes that carry the air in and out of the lungs. Coughing and mucus production can accompany the labored breathing of asthma, and one of the aims of therapy is to open up the airways and clear the lungs. Anything that helps move the mucus up and out of the body would certainly help.

Dr. Stephen Rennard at the University of Nebraska reported that chicken soup's effect might be due to its ability to block the inflammation and congestion caused by the movement of white blood cells (neutrophils) in the windpipe. In his experiment, the medicinal effect wasn't noticeable until the chicken soup was made with carrots, onions, sweet potatoes, turnips and parsnips.

Chicken soup doesn't have the same abilities as a modern antibiotic, but its powers are more wide-ranging, in a way: Antibiotics are only effective against bacterial infections, whereas soup can aid congestion brought on by either bacteria or viruses (like colds).

When thinking of making chicken soup, there are plentiful recipes to choose from. The basic recipe involves putting pieces of chicken (cooked or uncooked) into a large stock pot, then adding a couple of carrots, a large onion, a few stalks of celery, salt, pepper and enough water to cover. Then turn on the heat. Mimi Sheraton, in her book "The Whole World Loves Chicken Soup" (Warner 1995), supplies over 100 recipes from every corner of the globe.

With chicken soup, you get a satisfying, low-calorie dish that gives your body needed hydration and a potential vehicle for vegetables, protein and fiber. All this, along with an ability to help your body overcome that unwanted visitor. Not bad.

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: What is the comparison between the vitamin, mineral and lycopene content of sun-dried tomatoes versus cooked and fresh tomatoes? -- F.F., San Jose, California

DEAR F.F.: Sun-drying will reduce vitamins C and A, and, to a lesser degree, some of the other vitamins, but the mineral content is comparable. As for lycopene -- a reddish phytochemical that contributes to the tomato's characteristic color -- there isn't any significant difference between the levels in cooked, fresh or dried tomatoes. Lycopene is chemically bound inside the plant-cell matrix of the tomato. The cooking process breaks apart the intact cells and actually makes the lycopene more bioavailable, which means it gets absorbed with greater efficiency.

Sun-drying isn't the same as cooking. In the drying process, the cells shrivel and break as the water is removed, especially if heat is used. If lycopene absorption is your only consideration, the bioavailability of the lycopene will be greater with sun-dried than with fresh tomatoes.

Eating sun-dried tomatoes requires a bit of a chew; this not only helps release the flavors, but it helps mix the nutrients in the meal to facilitate absorption. All the better if there is a little olive oil (or any other oil) in the meal: Lycopene, like other carotenoids, is fat-soluble, so oil present at the same meal will help with absorption. And any lycopene that does not get absorbed still helps our bodies by contributing to the healthful environment in our intestines.

But we miss the point of healthful eating when we get overly focused on the individual substances in the whole foods we eat. The point is that you should enjoy healthful foods like tomatoes in whatever form you like best.

DEAR DR. BLONZ: Please tell me what is so bad about bananas. I have seen online ads saying things like "The 5 Foods to Avoid," and they always show a banana. I clicked on one of these and listened to a long spiel that never mentioned bananas, but had a pitch for a "bargain" $49 offer. I start my day with a banana. Most of my mother-in-law's diet was bananas. I had a dietitian once who didn't want to allow me bananas at all, but reluctantly let me cut one in half! I'm puzzled. -- R.P.

DEAR R.P.: What's bad about bananas? Perhaps bad PR, in that their commodity group does not pursue those who characterize the banana as less than "appealing" (pun intended). There is no science (or logic) behind the banana being touted as a poster child for "foods to avoid." One rare exception might be a person taking medication to control their potassium levels. Concern about the sweet taste in a ripe banana is also misplaced; it is the sugar added to processed foods that should be our concern, not that which is naturally present in a healthful whole food.

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: I find that even with 30 to 60 minutes of strenuous activity a day, I have trouble keeping my weight where I want it. I recently lost 20 pounds and now weigh 125 pounds, but if I were to eat the amount of food needed to supply all the Recommended Daily Allowances, which I assume are required for optimal health, that weight would come back. I also know that recent research shows that restricted caloric intake may actually improve health and extend life expectancy. So this is my question: Is it healthier to be slightly undernourished (not starving) as I am, or to be properly nourished (according to Food and Drug Administration guidelines) but somewhat overweight? -- F.S., Hayward, California

DEAR F.S.: My thoughts are that it is better to be well-nourished (along with being active) and slightly overweight. But I want to point out that the research you mention about caloric restriction and extended life expectancy does not involve any nutritional deficits. Your question needs to be reframed: Undernourishment or being overweight should not be embraced as your only options. Meeting the RDAs need not be a burdensome task.

Those who have been successful at losing weight have experienced the annoying tendency to regain at the slightest provocation. Just looking at food seems to make the numbers on the scale go up. With weight loss, you need to maintain your activity level and stick to a conservative eating pattern to, in effect, establish a new status quo. According to the Calorie Control Calculator (tinyurl.com/pozleth), a moderately active woman weighing 125 pounds needs approximately 1,900 calories per day. There should be no problem meeting your nutrient goals within that allotment.

Eating is one of life's great pleasures, and it makes no sense to get frantic about occasional nutrient lapses. The "R" in RDA stands for "recommended," not "mandatory." If you happen to fall short of your RDA every now and then, your body is not going to degenerate into a slab of broken bones or a mass of oxidized flesh. Just as it does with calories during a diet, the body becomes more efficient at nutrient conservation during times of disease, famine or nutrient inadequacy.

Know the good foods that your body needs, and keep your nutritional house in order as best you can. Healthful eating involves a plant-based diet that is rich in fruits and has plenty of greens and other vegetables, legumes, whole grains, nuts, seeds and dairy products, and an occasional meal with low-fat meat products. I have written an aisle-by-aisle guide of the best choices at the market, and it is online at no charge (goo.gl/ZDHHs5).

A helpful strategy is to have some nutrient-rich power foods in your diet. For example, a vitamin/mineral-fortified whole-grain cereal is a great way to start the day. You can opt for some blended vegetable juice instead of a diet soda, and some fresh fruit and nuts instead of chips. A cup of yogurt provides a calcium boost. Have a green salad with carrots and other fresh vegetables with one of your daily meals. For those on a weight-loss regimen in which fewer foods are eaten, or if there are special needs, it is reasonable to take a dietary supplement to help bolster the intake of certain nutrients, such as calcium and vitamin D.

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.