DEAR DR. DONOHUE: I had a long trip to Italy during which I experienced extremely swollen ankles. I have never had swollen ankles or feet. Can you explain why this happened? It took three days for my ankles to return to their natural state. – C.H.

ANSWER: Blood is not the only fluid that circulates in the body. Lymph is fluid that oozes out of blood vessels to keep tissues and body cells hydrated. It constitutes a second circulatory system. It is picked up by very special vessels – lymphatic vessels – that return it to the blood circulation.

Edema is swelling due to excess lymph fluid. It often first appears in the ankles and the feet. The causes for it are many. Heart failure is one. The heart pumps so weakly that more fluid than normal passes out of blood vessels and into tissues. Kidney failure is another cause. The body cannot get rid of fluid because the kidneys have shut down. Medicines such as the commonly used anti-inflammatory drugs can cause fluid retention and edema.

Not every cause of edema is an indication of a serious medical problem. Sitting for prolonged periods of time causes pooling of blood in leg blood vessels. Gravity is responsible. This is called dependent edema and is very common in people who cannot move about and must spend the day sitting in a chair. I believe this is what happened to you on your trip. I can’t give you a good reason why it took so long for the swelling to go down. That happens sometimes.

On your next trip, get up and move around. Wear elastic stockings during the flight. Compression keeps fluid in leg blood vessels.

DEAR DR. DONOHUE: I have been diagnosed with fructose intolerance. The doctor told me to stay away from sugar, fruit and sugar byproducts. Can you tell me more about fructose intolerance? – D.E.

ANSWER: Fructose is a sugar found in fruits, vegetables and honey. Many soft drinks, some candies and quite a few commercial foods and baked goods are sweetened with high-fructose corn syrup. It’s cheaper than regular sugar.

Some people don’t handle fructose well. They can absorb only small amounts of it. When they get too much, fructose reaches the colon undigested, and there, bacteria convert it into substances that cause bloating, gas, stomach pain and diarrhea. That’s fructose intolerance.

Table sugar (sucrose) is half-fructose and half-glucose, so people who are very sensitive to fructose have to watch the amount of table sugar they consume.

Fructose intolerance presents a major problem for people. The only way to surmount the problem is to enlist the help of a dietitian or nutritionist. The subject is too complicated for self-teaching.

There are inherited forms of fructose disorders that are very serious medical problems and cause grave troubles in infants.

DEAR DR. DONOHUE: My 33-year-old son had a colonoscopy, which disclosed that he had hundreds of colon polyps. There are too many to remove them all. Have you ever heard of someone having hundreds of polyps? Is it a cause for concern? – C.W.

ANSWER: Typically, three or fewer colon polyps are present at any one time. If there are more than 50 polyps, then the person is said to have a “polyposis syndrome.” Many of these syndromes are inherited, and some are dangerous.

Polyposis coli, for example, is a condition where there are hundreds, even thousands, of polyps in the colon. It is a rare illness and is usually inherited. However, it can spring up in a person due to genetic mutation that occurs during early development in the uterus. Polyposis coli can become colon cancer, and often the colon must be removed.

Peutz-Jeghers syndrome is another disorder with large numbers of polyps in the colon and small intestine. These polyps have a tendency to bleed.

Your son has to question his doctor about having one of these (and there are others) polyp syndromes, and he should do so right away.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.