Q. I have been trying very hard to lose weight. Unlike many dieters, I continue to eat potatoes, because I am really quite fond of them. My calorie book says that a medium potato contains about 100 calories. It does not really define a medium potato. What weight are they talking about?

A. "Medium" usually refers to a potato that weighs about 1/3 of a pound, or 5 1/3 ounces. A "large" potato is generally defined as one weighing a little over 8 ounces. And even that contains only 160 calories.

If you do not have a kitchen scale at home, you might want to take advantage of the scale in the produce section of your supermarket to help train your eye to recognize the size potato that meets your caloric specifications.

Keeping potatoes in your diet makes good sense, not only because you enjoy them, but also from a nutritional standpoint. Potatoes -- often referred to as "just starch" -- provide some good-quality protein as well as vitamin C, B vitamins, iron and other minerals. And they are low in fat.

Incidentally, if you want the sour-cream flavor without the calories that go with it, try part-skim yogurt, seasoned with chives. For a slightly different twist, add a few poppy seeds or toasted sesame seeds to the yogurt.

Q. As a child I had several food allergies which often created problems when I went to parties. I recently had a baby, and if possible, I would like to prevent her from developing similar problems. I was advised that breast feeding might be helpful in reducing the likelihood that she would develop food allergies. I'm already nursing her, but can you make other suggestions about her diet?

A. While the routine use of dietary measures to prevent allergies is open to debate, there is some evidence that certain steps may have value. And we can tell you about some of the recent research that has examined the relationship between diet and allergies -- particularly focusing on preventive measures that might be effective in infants with a family history of allergies.

For example, it has been reported that infants who are exclusively breast-fed for the first months of life experience a lower incidence of eczema. In another study, when foods known to be potent allergens -- cow's milk, eggs, chicken and wheat -- were purposely withheld for the first nine months of life, there was a decreased incidence of allergic responses in the infants.

These pieces of evidence are interesting. But they should not be used as a framework on which to plan your daughter's diet. Instead, we would urge you to talk to your pediatrician about outlining a pattern of introducing solid foods which might help to minimize her risk of developing allergies.

Q. I recently joined my high-school track team and began doing a lot of reading about the relationship between diet and athletic performance. There is one point on which I would like some clarification. While I realize that fluid replacement is important for distance runners, it's not clear whether the fluids should be hot or cold or whether temperature makes a difference at all. Can you tell me?

A. Yes, temperature does make a difference. One study found, for example, that while 50 percent of a solution taken at 5 degrees centigrade (41 fahrenheit) left the stomach within 15 minutes, only 27 percent of a solution of the same drink taken at 35 degrees centigrade (95 fahrenheit) left the stomach in that amount of time.

Cold liquid reduces stomach temperature and this may increase the gastric motion and rapid flow through to the intestine where it is absorbed.

We might also mention that in addition to temperature, volume seems to have an important effect. Increases in fluid intake up to about 20 ounces cause a progressively greater emptying rate and consequently promote more rapid restoration of fluids to the body.