As Roseanne Roseannadanna would say, "It's always somethin'."

Now it's zinc and zinc deficiency. Dr. June Kelsay, a research nutritionist at the Beltsville Human Nutrition Research Center, has observed zinc deficiency in subjects who eat a lot of spinach along with a high-fiber diet. However, spinach taken with a low-fiber diet creates no deficiency, Kelsay has found, and a high-fiber diet alone apparently causes no deficiency.

This doesn't appear to be of great concern to most Americans, says Kelsay, because they typically consume a lot less fiber and spinach than the experiment participants. (Members of the study group ate 25 grams of fiber a day -- about two servings of fruits and vegetables at every meal -- plus spinach every other day.)

But this (and additional) research raises new questions about zinc, already on the scene as the latest nutritional cure-all. Zinc enthusiasts claim it cures cold sores and improves sex life. While such allegations carry zinc's function to an illogical extreme, zinc deficiency causes concern. The research drives home the point that nutritional deficiencies can be linked to all kinds of diseases.

Dr. Robert Henkin, who studies molecular nutrition and sensory disorders at Georgetown University, predicts that as more is learned about zinc, more will be discovered about zinc deficiency, which "may have some relevance in the latter part of the century."

In his practice, Henkin sees up to 50 zinc-deficient adults each week. From all over the world come people suffering from altered perceptions of taste and smell. One recent visitor from Ohio had lost his sense of smell completely. To some, everything tastes metallic. In the most severe cases, people have simply stopped eating. According to Henkin, these are just a sampling of the 4 million zinc-deficient adults in the United States.

Zinc--which Henkin calls the "key tissue mineral"--is not as easy to measure in the body as iron (the key circulating mineral), and a deficiency is therefore hard to diagnose. If a patient approaches his doctor because he "doesn't feel well, can't taste very well, can't smell very well," it's unlikely that the practitioner will leap to the conclusion that the patient is zinc-deficient.

Only 25 percent of those who suffer this sensory dysfunction are actually low in zinc, says Henkin. Of those who are, deficiency results from any number of problems, only one of which is inadequate dietary zinc. As is the case with iron, the absorption, transport or actual metabolism of zinc might be the culprit.

But Henkin cautions against people self-diagnosing ailments and treating sundry symptoms with zinc supplements "[Zinc deficiency] isn't a disease of the week, this is a real problem. It would be wrong to oversimplify this."

Zinc deficiency, according to Henkin, stunts the growth of perhaps "10 percent of the growth-retarded children" in this country. Some studies show that these children--commonly from middle-class backgrounds--often get adequate dietary protein, but a diet with "perfectly normal amounts of protein can be completely bereft of zinc," says Henkin.

He sees children who have appetite problems, growth problems and peculiar diets--finicky eaters who get plenty of milk and bread and french fries but very little of zinc-rich meats, nuts and seeds.

Responding to the suggestion that nearly all children are picky eaters, Henkin replies, "Picky is fine, but when they pick foods low in zinc, it becomes a problem." He adds that the problem affects "enough children that you have to worry about it."

New discoveries lead to new solutions for old problems. Henkin says that with scientists "rolling back the borders of ignorance in medicine," nutrition will become an increasingly important focus in diagnosing disease.