No single volume of an Annual Review can hope to encompass a subject as wide as that of nutrition, which spans from findings and methodologies of basic and molecular sciences to the applications and health-related concerns of humans. It is obvious, then, that those of us responsible for reviewing this profession must select what seems timely and representative. Only over the course of several years, and with emphasis limited to nutritional science, can there be reasonable coverage of most significant topics in the discipline of nutrition. This volume, our eighteenth, reflects the usual diversity in categories of nutrients and their disposition in humans and other species. Attention is given to the macronutrients: diversely on lipid-related topics and in chapters on dietary fructans by Roberfroid & Delzenne, on meat production by Wray-Cahen et al, and on nitrogen cycling in the gut by Fuller & Reeds. Micronutrients are addressed in a chapter by Eide on metal ions, from their transport in a simple eukaryote, and in reflections by O'Dell on the "galvanizing trail" in higher animal species. Vitamins and other cofactors are covered in chapters by Castenmiller & West, Gregory, and McIntire. The interesting relationship of oxidative stress, selenium, and viral infection is brought out by Beck & Levander, and the use of "transgenic mice in analysis of metabolic regulation" is reviewed by Bosch et al. There are issues of diet as related to chronic disease, as in the chapters by Clinton & Giovannucci concerning prostate concer, by Kerner & Hoppel on management of genetic disorders of carnitine metabolism, and by Wood & Fleet on the polymorphisms of vitamin D receptors relating to osteoporosis.

The periodic updating of topics requires the collation of current information into review chapters, serving the purpose of informing us on "gains" in our subject. However, an additionally worthwhile purpose of any review of an active, growing discipline is the identification of gaps in our knowledge. A succinct mixture of the latter with the larger corpus of the acquired facts should induce investigators to follow productive paths of inquiry. Suggestions for further research are often, but not always, made by authors of chapters, the topics of which usually must be narrowly circumscribed. Hence, in many cases major research that spans subjects, especially those bridging basic to applied, are not adequately covered. When not too tangential to the constrained topic (and allowable length), it may be helpful in the concluding portion of a chapter to indicate where the subject itself should be expanded and when important extrapolations to other areas or applications are warranted. For example, in covering new knowledge on some aspect of a particular vitamin, without thoughtful additional connection to the human weal, it would not be realized that we have little specific information on the requirements of any vitamin for those who are postinfancy but preadolescent. Most of our estimations for those in this vulnerable age range are based on interpolative guessing between "adequate intakes" for infants, taken as the concentrations in normal mother's milk, and levels obtained from studies of adults, ideally with convergent data from intake, excretion, and functional tests. It may be instructive for our readers to have terse connection between "gain" to "gap" made by our authors, who could thereby stimulate others toward appropriate further investigations. By this statement, I hope to encourage such thinking for contributors to future volumes. Our profession would be well-served to receive constant stimulus for research directions based on currently acquired knowledge such as should be condensed in timely reviews. There is really so much we do not know but should.

Credit for the informative value of the Annual Review of Nutrition goes to the contributors of our chapters, who are only modestly beset by the Editor and his fine Associate Editors, Drs. Denny Bier and Alan Goodridge. The suggestions for authors and topics are generated by our Editorial Committee, which is often willing to entertain the recommendations of our readers. Dr. Janet Carlson King has joined this group. Our Production Editor, Robbie Parmer, really clarifies the language and glues the whole together while additionally serving as Managing Editor for Annual Reviews, ably led by Dr. Sam Gubins.

Donald B. McCormick, Editor