I suspect that most parents don't realize that some vegetables have low levels of toxicity that their children can detect, but they often intuitively make such vegetables more palatable by masking the sharp flavors, such as by placing sugar on carrots, and cheese sauce on broccoli and cauliflower.

This raises an interesting issue. Do children who most dislike such vegetables have a lower tolerance for the toxins than children who like the vegetables? Can forcing children to eat something that nauseates them result in learned strong negative adult rejection? Should children be taught to put up with a little discomfort if the disliked food provides important nutrient values? Good questions. No simple answers.

Food preferences are obviously more complicated than toxin levels. For example, an earlier column reported that smell is more important than taste in the recognition and selection of many foods, and the common use of herbs and spices enhances this process. Cultural differences in preferences also exist. Many Asians consider the smell of cheese to be obnoxious, and the odors of sauerkraut and pickles similarly attract and repulse people. On the other hand, everyone seems to like the odor of vanilla (which is somewhat similar to breast milk).