DEAR DR. DONOHUE: My son, 34 years old, has had eight kidney stones in the past 10 years. His doctor hasn’t said anything about prevention. What can he do to end this? Could this all be genetic? His older brother has had one stone attack, and his father had stones. If it is genetic, does that mean he’s bound to have them again and again? – D.D.

ANSWER: In some families, stone formation is greatly influenced by genes. If one family member has had stones, the risk for other family members having a stone is twice the risk of people with no family history of stones. Even if genes are involved, your son can do much to prevent repeat occurrences.

He has to know what kind of stones he makes for specific advice on prevention. The most common kind is calcium oxalate, and what I am about to say addresses those stones.

Foremost is drinking plenty of fluid, a little more than 2 quarts (2 liters) a day. He’ll know he’s drinking enough fluid if his urine is colorless. The fluid doesn’t have to be all water. He can pick whatever he wants, but he should stay away from grapefruit juice. In summer months, he must be really vigilant about fluid intake, since people tend to dehydrate themselves in warm weather.

Reducing the amount of meat in the diet helps put a lid on stone formation. So does limiting salt. Salt encourages the excretion of calcium into the urine, and that, in turn, increases the chances of a stone. Potassium has the opposite effect, so fruits and vegetables – good sources of potassium – can be eaten without restraint. Strange as it sounds, he doesn’t have to avoid calcium foods. Too little dietary calcium fosters stone formation. If his stones were calcium oxalate stones, he should pay some attention to the amount of oxalate he takes in. Oxalate is found in rhubarb, spinach, sweet potatoes and beets. Sugar also influences the amount of calcium lost in the urine, so he has to curb, somewhat, a sweet tooth.

Your son has had an inordinate number of stones. A doctor has to check him for things that promote kidney stone formation. Overactive parathyroid glands are an example of one such condition.

DEAR DR. DONOHUE: Without trying, I have lost 20 pounds. I am 5 feet, 10 inches tall, and my present weight is 145 pounds. I look skinny. I’ve been eating everything in sight, but I can’t gain any weight. I also take a supplement. What’s going on? – P.R.

ANSWER: Weight loss without an effort to do so is a sign that something has gone haywire, even if the person has no other symptoms. I take it you have no other symptoms – things like diarrhea, fatigue or pain. Am I right?

You have to get to the bottom of this with a doctor. It’s not something you can do on your own. The cancer question pops up, and it’s the question that must be answered quickly. You could have one of the malabsorption illnesses, conditions where food isn’t digested and absorbed. Celiac disease is an example. An overactive thyroid gland leads to weight loss.

You’re either burning excessive calories or losing them in some other way. That’s the only explanation for a loss of weight.

I’m not going to make a long list of possible causes. I do strongly urge you to get to your doctor quickly. This can’t be ignored.

DEAR DR. DONOHUE: You’ll think I have nothing better to do when I ask you this question. I added up my LDL cholesterol and my HDL cholesterol, and it doesn’t equal my total cholesterol. Why not? – D.H.

ANSWER: They don’t add up because there’s another kind of cholesterol – VLDL cholesterol, very low density lipoprotein. It’s not usually recorded on lab slips. If it were, you would come out with the total number.

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