Q: I am one of those women who has a lot of trouble getting all the calcium I need without consuming too many calories and gaining weight. The problem is compounded by the fact that while I can drink low-fat milk, I don't like skim milk. Can you please tell me whether there is any advantage to buying the protein-fortified low-fat milks, in terms of contributing significantly more calcium?

A:The protein-fortified varieties do offer some advantage. A cup of 2 percent low-fat milk provides about 120 calories and almost 300 milligrams (mg.) of calcium. If the total nonfat-milk solids added is less than 10 percent, there is no appreciable difference. The same cup of milk would contain about 125 calories and 313 mg. of calcium. However, if you choose low-fat milk labeled "protein-fortified," which contains at least 10 percent nonfat milk solids, you would get about 137 calories, but the calcium level would be up to 250 mg. per cup.

A cup of 1 percent fat milk without added milk solids contains 102 calories and 300 mg. of calcium. If nonfat milk solids are added at levels below 10 percent, neither the calories nor the calcium climb appreciably. However, milk labeled as "protein-fortified" provide 119 calories per cup and, like the 2 percent fat, protein-fortified milk, 350 mg. of calcium.

Q: I have heard that the use of aspartame has been linked with headaches in some people. Is this true?

A:A number of people have claimed that they experienced headaches after using aspartame. Yet a study conducted by researchers from Duke University was unable to demonstrate such an effect. Forty adult subjects were selected for the study from a group of individuals who had complained of symptoms associated with aspartame use, either to the manufacturer or to the FDA. They were given either a large dose of aspartame, about equal to that found in no less than 4 liters of carbonated soft drink, or a placebo. Neither the subjects nor the investigators knew which was being given on any single occasion.

Twenty-six of the 40 individuals reported having headaches during the experiment. Eight subjects had headaches while receiving aspartame, 12 while receiving the placebo, and 6 while getting either one. Statistically speaking, there was no difference in the incidence of headache, of other clinical symptoms, or in the results of a number of laboratory tests associated with either aspartame or the placebo. These results simply do not provide evidence that aspartame, even when administered in amounts far larger than anyone would normally consume, causes headaches.

Q: Recently I prepared a buffet luncheon for guests. Among the items was pasta salad containing a medley of raw and cooked vegetables and tossed with a vinaigrette dressing. Everything was fine, except that the lightly cooked broccoli turned an unpleasant yellow color. What caused that to happen?

A:Heat and acid combined to produce the color changes. Chemically, chlorophyll resembles hemoglobin, the oxygen-carrying pigment in red blood cells. But instead of iron, the chlorophyll pigment contains magnesium. With heat, the magnesium is rather easily dislodged and replaced with hydrogen. The color changes are partly explained by new compounds formed in the process, one of which results from the conversion of chlorophyll which was a blue-green hue to one which is now a pale greenish gray. The other, which was a duller yellow green, turns a more olive shade.

Beyond that, however, the intense green chlorophyll masks other yellow and orange pigments in green plants. When it is destroyed, these colors show up. In combination with the compounds formed when the chlorophyll is altered, the net effect is a muddy olive color, and that effect was enhanced by the addition of extra acid in the form of vinegar.