DEAR DR. DONOHUE: I have been diagnosed with thalassemia. My mother was diagnosed with it, too. I understand that it is hereditary, but I do not quite comprehend all that it means. To the best of my knowledge, I think it makes us appear to be anemic. I feel tired all the time. I was told to take additional iron. Is it advisable to do that? — J.R.

ANSWER: Thalassemia isn’t one, but a group of inherited anemias. Its name is a Greek word for “sea.” The sea is the Mediterranean Sea, and the countries that border it are the places with the highest incidence of thalassemia. However, it’s also found in parts of India and Central Africa.

Anemia is a deficit of red blood cells. Signs of anemia are fatigue and breathlessness on slight physical exertion.

People who inherited two genes, one from the mother and one from the father, come down with anemia. People with one gene don’t have anemia; they have what’s called thalassemia minor. That’s what you and your mother have. Thalassemia minor rarely, if ever, produces any symptoms. It can be mistaken for iron-deficiency anemia, but iron is not recommended for thalassemia minor. The person doesn’t need it. It doesn’t do any good, and it can cause trouble by leading to an overload of iron.

Tell your doctors you have thalassemia minor. They’ll tell you to steer clear of iron.

I don’t know what’s causing your tiredness, but it isn’t thalassemia minor.

DEAR DR. DONOHUE: I’m confused by fats. What’s the difference between saturated and unsaturated fat? What are trans fats? How can you tell the difference? — R.T.

ANSWER: Saturated fats are fats that hold all the hydrogen they can; they’re saturated with it. These are the fats found in and around meats, in whole dairy products (whole milk, butter, cheeses) and in many fried foods. Saturated fats stimulate the liver’s production of cholesterol. The liver is the source of most blood cholesterol.

Unsaturated fats are missing some hydrogen atoms. They don’t stimulate cholesterol production as much as saturated fats do, so they’re less involved in clogging arteries. Vegetable oils, olive oil, canola oil, fish, nuts and plant-based foods are sources of these fats.

Trans fats are, for the most part, filled with hydrogen from manmade processing of many foods. They are the worst when it comes to artery-clogging. Many commercial foods — cookies, crackers, baked goods — have trans fats. They increase the shelf life of manufactured foods. Trans fats must be listed on food labels. Keep them to a minimum.

DEAR DR. DONOHUE: I recently had a bone-density test that was quite different from previous bone-density tests I’ve had. The recent test was done on my wrist and not on my limbs, as in the past.

Can the reading of my wrist be as good as the testing that used to be done? — M.C.

ANSWER: DEXA, dual-energy X-ray absorptiometry, is the standard test for determining bone density and for diagnosing osteoporosis. The spine and the hip are the two places most commonly used to take the DEXA reading. However, other bone sites can be used: the wrist, the radius bone in the forearm and the tibia in the lower leg. Bones at different body sites have different densities.

The reading at a particular site is compared with the reading taken at the same site in healthy, young people. That is the basis of the T-score. The wrist is a valid place to take the test.

A T-score of or less than -2.5 is considered to be osteoporosis.

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.