Despite most people's total reliance on the grocery store, business continues to grow at the nation's health food stores - to the tune of $2 billion in sales last year.

But a survey of Boston health food stores by writers for Tufts University found many items on the shelves of such stores are no different than those at the local supermarket, despite packaging that stresses "natural" ingredients.The health food products often cost much more than equivalent items on grocery store shelves.

The writers, working for the university's Diet & Nutrition Letter, found two 14-ounce catsup bottles, one by Heinz selling at a supermarket for 79 cents, another selling for $2.29 at a health store. The label on the more expensive bottle boasted "no preservatives or MSG" (monosodium glutamate, which may cause allergic reactions in some people).

The fine print of the Heinz bottle, however, reveals it too contains no preservatives or MSG. Aside from the kind of sugar used - honey in the expensive catsup, corn syrup in the other - the products were essentially identical.

Price disparities were found for similar products that included cereal, yogurt and baby food.

* Single copies of the list can be obtained by sending a self-addressed business-sized envelope with 50 cents return postage to: Mail-Order Organic, CSPI, 1501 16th St., N.W., Washington, D.C. 20036.