Q. Unfortunately, at 225 pounds I weigh about 100 pounds more than I should. Recently I have started to diet and am trying to get exercise. A while ago you wrote about caloric expenditures for tennis and bicycling, but neither of these is appropriate for me. Can you tell me the caloric cost of the activities I can do, such as walking and gardening? I walk about 30 minutes a day, and work in my garden for about an hour.

A. At 225 pounds, strolling at the rate of two miles per hour, you would burn about 155 calories in 30 minutes. If you doubled your pace, you would use approximately 270 calories in the same period.

The number of calories you expend gardening depends on the activities involved. Light gardening would burn about 320 calories in an hour, while more vigorous weeding might take care of as many as 530.

For a table of caloric expenditures by individuals at different weights involved in a variety of activities, you can consult "The Partnership Diet Program" by Dr. Kelly Brownell (Rawson Wade, 1980). It also provides helpful suggestions for dieters seeking guidance about behavior-modification techniques for weight control. (Inasmuch as the book is now out of print, you may have to look for it in your local library.)

Q. While buying my children a loaf of raisin bread, I was surprised to see that one brand was labeled as containing "50 percent more raisins" and another as having "30 percent more raisins." My question is, "More than what?" Is there any advantage beyond taste to the breads with more raisins?

A. Raisin bread, if sold across state lines, is one of the foods covered by a Standard of Identity. This means it has to conform to a legally defined recipe. It must contain not less than 50 parts by weight of raisins for each 100 parts by weight of flour used in the loaf. So the raisin content for the "50 percent more" variety would be 75 parts per 100 parts of flour, and for the "30 percent more," 65 parts per 100 parts of flour.

Comparing nutrient labels and prices, we found no important nutritional difference between the regular and the special breads. And while the brand containing 30 percent more raisins cost only 8 cents more than the standard loaf, the one with 50 percent more cost an extra 30 cents. In other words, the decision about which type to buy is a matter of taste preference and budget constraints, not nutritional issues.

Q. Every summer I grow zucchini and give most of it away because my children reject it at the dinner table. I realize that a sales pitch focused on nutrition is unlikely to change their minds, but I often wonder whether this vegetable has any particular nutritional value. Can you tell me?

A. Nutritionally, zucchini's strongest selling point is its low number of calories. A whole cup contains just 36 calories, nearly all of them from carbohydrate. It is also an excellent source of potassium; a cup has as much as you would get from six ounces of orange juice. And it contains some B vitamins and iron.

If you have not given up on growing and serving it, we have a couple of suggestions that might boost its popularity in your house. One reason zucchini is often rejected is that it tends to turn limp when boiled. If you have been boiling it, you might try steaming it until barely done.

Another way to keep it crunchy is to saute' it in a little oil. With this method, there are many possible variations. For example, in one very tasty version, a bit of garlic is first browned, and then lightly cooked mushrooms are added to the zucchini for a brief stir-fry. The mixture is seasoned with a dash of hot pepper oil and a taste of teriyaki sauce.

Q. I have recently inaugurated a regular exercise program. I play tennis three days a week and go biking at least twice a week. I am certainly feeling more fit, but would like to know how many calories I am burning in these activities.

A. Caloric expenditure depends on several factors, including the vigor of the exercise and the size of the individual performing it. Smaller, lighter people burn fewer calories in a given period of time than do larger, heavier ones.

An individual who weighs 125 pounds would expend about 335 calories in an hour of tennis, while moving an additional 25 pounds around the court would burn an extra 65 calories in the same period. (Time spent chatting at the net is not included.)

Similarly, while biking at a cruising speed of 5.5 miles per hour, the lighter person would use up about 250 calories and the heavier one about 350. At the faster pace of 13 miles per hour, the lighter individual would burn 535 calories and the heavier person 640.