DEAR DR. BLONZ: Thank you for your column on intestinal gas. There is one thing you could add that might be helpful next time the subject comes up: Some parasitic infestations cause chronic cyclical gas episodes.

As a Peace Corps volunteer in the 1960s, I was exposed to many African parasites, and brought at least one of them home. For the next 15 years, I was afflicted with periodic bouts of noxious flatulence, about two days every two weeks. I repeatedly sought medical help (and received lots of ineffective information) before I found a doctor who had experience with tropical ailments. He said, "I don't know what you've got, but Atabrine might clear it up." I took the Atabrine for a week, and it was over. Thus, with one bottle of pills, a 15-year social problem was ended.

Most likely, I learned afterward, the culprit was Giardia lamblia. This organism has become very widespread in the past few decades -- possibly due to folks like me coming home from Africa, then going backpacking in the mountains and woods.

Giardiasis is not particularly debilitating. After a single initial siege of sulfurous burping, the only long-term symptoms seem to be the periodic attacks of stinky gas. I suspect that lots of folks are living with giardia, and occasionally casually asking their doctor about it. Just as I did for a decade and a half, they are receiving suggestions to avoid beans, cabbage or processed meats. Since a bout of gas only lasts a couple of days, the "cure" seems to work, but the trouble will be back in a couple of weeks.

Atabrine, an older quinine drug, probably isn't used much anymore, but there are plenty of newer drugs that will clear giardia up quickly; the trick is finding a doctor who has experience with parasites. Since parasites in general are less common in the U.S. than in Africa, this can take a while. The worst thing that can happen is to get misdiagnosed and mistreated for something else. -- D.R., Orinda, California

DEAR D.R.: Your informative letter speaks to the necessity of seeking assistance from someone with expertise in the area of concern, and of giving your complete background to your health professionals. There is so much information available online, but that places the responsibility on us to be diligent in where and how we search. Stick with academic sites (ending with .edu) or others that rely on evidence-based medicine. I have a list of medical resources at blonz.com/med.htm that can serve as a guide.

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: We are entering the season where farmers' markets become loaded with fresh fruits and vegetables, and I wanted your take on juicing. Is it more healthful to eat fruits or vegetables, or to juice them? How about fiber, because you pretty much throw that away? -- T.T., Hayward, Calif.

DEAR T.T.: Farmers' markets are a great way to see what's in season, support local agriculture and get some walking in as well. In answer to your question, let me say that it is very healthful to consume lots of fruits and vegetables, period! Whichever way you choose will work in the big scheme of things.

Some advantages to eating fresh produce (without juicing) are that you get individual tastes, textures and an appreciation of how flavors differ between varieties, growers and throughout the growing season.

Another big plus is that it tends to take more time to eat the produce than to drink its juice -- an aspect that should not be discounted. It takes a while for the brain to get the signal that the body has had enough to eat, and when we rapidly eat until stuffed, we've usually had too much. Wolfing down a meal is not advised, whether the meal is a paragon of healthfulness or fast-food dreck. The slow enjoyment of a fresh fruit or vegetable keeps control in the loop.

Juicing, particularly if fibers are not present, can provide a load of sugars in easy-to-consume form. As with any eating, portion control needs to be exercised, but the flavors can be seductive. The great advantage of juicing is that it can provide a convenient way to include new varieties of fruits and vegetables in your diet.

As for juicers, there are three basic types: extractors, masticators and blenders. Extractors are the most popular type. They grind the food with a high-speed spinning dish that traps the pulp, and often have an ejector that deposits the pulp in a convenient bin. The masticator type of juicer "chews" up the food at a slower speed, then makes juice by mechanically pressing the ground-up mash against a screen.

Finally, there are specialized blender/juicers that grind the entire fruit or vegetable, pulp and all. This is the one type of machine that doesn't remove the pulp; as a result, juices from these machines retain the food's fiber. The tradeoff, however, is that the output can end up more slushy than juicy.

Price vary greatly among juice extractors, with the differing price tags -- from about $45 to well over $300 -- often reflecting the power and noise-dampening of the motor, the pulp capacity and the ease of cleaning. The masticators and blender/juicers tend to be in the $200 range.

There is really no "best" method; it's all a matter of taste and affordability. Be sure to sample some juice from the type of machine you are considering before you buy: Find a juice bar in your area, or arrange for a demonstration at the store where you are considering making your purchase. It is also essential that you know how a prospective model needs to be cleaned. If cleaning is a bother, the machine may sit crusty and unused.

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 have been active most of my life and have always eaten well. As time has passed, my abilities have decreased (as expected), and now that I have just turned 70, I am wondering whether there need to be changes in what I eat and drink. My partner and I take a fitness class that is promoted to improve flexibility, balance and strength. -- O.M., Chicago

DEAR O.M.: Nutritional requirements for active older people are not much different from those who are sedentary, with two exceptions: water and calories. Both require a varied diet that focuses on nutrient-dense fruits, vegetables, grains, nuts, seeds and dairy products, along with high-protein foods such as fish, poultry and meats. As an active person, you will simply require more total calories than a sedentary peer.

Our metabolisms go through changes as we progress through midlife to our senior years. Most of us become less active, and muscle mass shrinks following the dictates of the body's "use it or lose it" mandate. Smaller, less active muscles require fewer calories; think of the analogy of the gas used by an eight-cylinder versus a four-cylinder engine.

Over time, some aspects of the digestive system become less efficient, and our ability to sense thirst diminishes, which can result in dehydration. Mineral loss in our bones can begin to become apparent at about age 40. We tend to get a bit shorter (although most tend to think their height is the same as it was in their youth), and this means an increased risk of osteoporosis. There is less range of motion in the joints due, in part, to fewer demands on the way we move. This is the script for a sedentary lifestyle, but more active types, especially those who include flexibility and movement exercises, will experience fewer of these negatives.

Though you say you have long been active, I would like to spend some time addressing any readers who want to start becoming more active in their later years.

First of all, start slowly. Touching base with your health professional makes sense if there are any health issues. While muscles don't respond as they did in your youth, you will slowly adapt to your new routines. I encourage all to consult with credentialed trainers who can map out a reasonable course. An important benefit is that muscular work helps you hold on to your bone strength, and as long as you go slowly and don't overdo it, the joints will regain and retain more flexibility to help support the physical activity. This will also help improve your balance. The circulatory system also improves, providing fuel and removing waste materials from the working muscles. You may also find improvements in your sleep habits.

A word on water: Drink some before, during and after exercise because it helps keep the body cool through perspiration. In addition, water facilitates the shuttling of waste products from energy production out of the body through the urine. Dehydration, even when mild, impairs performance and can cause the body to overheat and malfunction. This can be especially dangerous in the older athlete, because the kidneys do not operate as efficiently. Because one's awareness of thirst can be lost during exercise, it's best to make drinking water a part of any exercise routine.

You might want to take a complete set of body measurements before you start. Finding that your clothes begin to fit differently is great feedback. Hunger may increase, but try to focus on fruits, vegetables and other nutrient-dense foods, all eaten slowly. Keep track of your weight weekly, but be less concerned with the numbers than with the knowledge that you are doing things for yourself that nobody else can do.

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.