DEAR DR. ROACH: I’m 64 and healthy. I’m very petite at 4 feet, 10 inches tall. I’ve had a low weight most of my life, keeping around 95 pounds. Two years ago, after retiring and being less active, I got up to 110 and maintained it for a year.

Then I got married and am active again in the garden, walking and traveling. I’ve dropped back to 100 pounds, but I have not changed my diet in any way. My arms and legs are very, very thin, whereas my trunk is normal for my size.

I eat a good breakfast every day. I eat a good dinner of a variety of meats, vegetables and potatoes/pasta. I find it hard to eat any more than that a day.

What is a good way to gain weight without having to eat more meals per day? — S.F.

ANSWER: I am not sure why you want to gain weight. I think your body is fine at the weight you are, and that you should concentrate on enjoying food and your activities.

Your body mass index, an imperfect way of normalizing height with weight, is 21, which is at the low end of the desirable range, but not so low that it puts you at health risk.

Since muscular arms and legs are associated with lower risk of disease as you age, I would ask you to consider a weightlifting program, which doesn’t have to be anything more complicated than a few-pound dumbbell that you do various exercises with; however, a trainer or physical therapist can help teach you how to use them most effectively. Weight training also helps reduce risk of falls and of osteoporosis.

A very recent study showed that strong grip muscles are associated with lower mortality; however, I think this is more likely to represent overall levels of health and disability than it is that improving grip strength makes you live longer.

DEAR DR. ROACH: I’m a woman with recurring urinary tract infections over the years. In my past two episodes, although the urine tested positive in the doctor’s office, when the results came back from the lab, there was no reported infection. In both these cases, I had the usual UTI symptoms of intense burning and urgency to void. In addition to my internist, I’ve seen a urologist, and neither could explain these test results. I’d appreciate knowing what your thoughts are. — Anon.

ANSWER: The urine dipstick in the doctor’s office looks for an enzyme made by white blood cells in the urine, whereas the lab looks for the bacteria themselves. Your situation is not uncommon, and there are several possible reasons why this might happen.

Given your symptoms, one likely possibility is that you have an infection in the bladder or urethra (the short tube that drains the bladder), an area that is very sensitive to the inflammation caused by bacteria and white blood cells. However, the level of infection shown on the culture results may be so low that the lab reports it as negative. There are a few infections, such as chlamydia and tuberculosis, that don’t show up on a standard culture. Treatment with appropriate antibiotics in this situation resolves the symptoms. If it doesn’t, then looking for another cause is indicated.

There are non-infectious causes of the burning sensation. Post-menopausal women can get atrophy, which usually is treated with topical estrogen. Interstitial cystitis is a possibility, and the symptoms in IC usually are temporarily relieved by voiding. Concentrated urine, small stones and trauma also can cause burning sensation. However, a positive dipstick indicates the presence of white blood cells in the urine, so I think infection, interstitial cystitis and stones are the most likely possibilities.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Health newsletters may be ordered from www.rbmamall.com.