The biological importance of milk to all mammals, including humans, is evident from historical and physiologic perspectives. The survival of human infants depended on breastfeeding until early in the twentieth century when substitutes for human milk were developed, leading to a marked decrease in breastfeeding. Subsequent reports of lower morbidity and mortality among breastfed infants compared with formula-fed infants stimulated a reexamination of infant feeding practices. Questions have also been raised concerning the role of breastfeeding in promoting optimal infant growth, nutritional well-being of the infant, and bonding between mother and infant. Relatively little attention has been given to the mother and her needs.

Growing concerns among health professionals led to the first Surgeon General's Report, Healthy People: The Surgeon General's Report on Health Promotion and Disease Prevention (Department of Health, Education, and Welfare, 1979), and subsequently to publication of Promoting Health/Preventing Disease: Objectives for the Nation (Department of Health and Human Services [DHHS], 1980). The latter report set breastfeeding of 75% of all infants at hospital discharge and 35% at 6 months of age as an objective to be attained by 1990. Shortly thereafter, the Surgeon General's Workshop on Breastfeeding and Human Lactation further emphasized that objective and provided a framework for its implementation. The breastfeeding objective has not yet been achieved; in fact, the rate of breastfeeding at hospital discharge has decreased since the time of the Surgeon General's Workshop. Factors such as lack of specific policies for paid maternity leave, lack of child care facilities at the mother's place of employment, or lack of adequate facilities for pumping and storing

human milk might have contributed to the failure to reach the breastfeeding objective. The objective is reaffirmed and expanded in the Year 2000 Objectives for the Nation (DHHS, 1990).

Since 1980 there has been a marked increase in research on human milk, with special emphasis on its composition and role in promoting or sustaining the well-being and development of the infant. Six workshops on human milk and lactation were sponsored by the National Institute of Child Health and Human Development between 1982 and 1990. The third workshop was dedicated to maternal and environmental factors that affect human lactation, but the influence of maternal nutrition on lactation was reviewed only briefly.

Many studies of maternal and child nutrition have been conducted by committees of the Food and Nutrition Board under the sponsorship of the Office of Maternal and Child Health of the DHHS. However, the study reported in this volume is the first one directed specifically toward maternal nutrition during lactation.

Although great progress has been made in understanding the process of lactation and in characterizing and quantitating the composition of human milk, less progress has been made in linking the nutritional status of lactating women with various outcomes of breastfeeding. The subcommittee carefully examined evidence pertaining to the demographics of breastfeeding; lactation performance, including milk volume, duration of lactation, and milk composition; infant outcomes such as nutritional status, growth, development, morbidity, and mortality; and maternal long-term health outcomes. Special effort was made to search for studies to investigate the impact of maternal nutrition on these outcomes and studies of the effects of breastfeeding on maternal nutrition.

This volume provides information that will help researchers, students, and health care providers understand how nutrition of healthy women relates to various outcomes of lactation in the context of many other contributing factors. It is also intended to aid in formulating guidelines for clinical application in the United States. Finally, the report highlights gaps in knowledge and recommends directions for further research.

This volume begins with a summary of the report and its principal recommendations. Chapter 3 addresses the question, "Who is breastfeeding?," identifying breastfeeding rates in the United States by different demographic characteristics (such as age, ethnic background, region of the country, and employment status). It also provides a historical perspective of the incidence and duration of breastfeeding in the past century.

Chapter 4 examines anthropometric, biochemical, and dietary methods for assessing the nutritional status of lactating women and points out their uses and limitations. Since most interventions designed to improve nutritional status

act to increase intake of nutrients in short supply in the diet, the subcommittee tabulated and interpreted nutrient intake data from studies of lactating women. Chapters 5 and 6 contain discussions of the volume and composition of human milk and explain factors that must be considered when evaluating the impact of maternal nutrition on these two lactation outcomes. These chapters also provide the basis for estimating the range of the mother's nutrient losses resulting from breastfeeding.

Although infant growth, development, and health are key outcomes of breastfeeding, the effects of maternal nutrition during lactation on these outcomes have been largely ignored in the literature. To the extent possible, Chapter 7 reports links between the nutrition of the mother and the nutrition and growth of the nursing infant. Since a slower than expected rate of infant weight gain may be given as a reason to discontinue breastfeeding, the subcommittee paid special attention to the assessment of the growth of breastfed infants. The possibility that maternal nutrition may influence infant health through altered immunologic function and the links between maternal food intake while lactating and infant health are also considered in Chapter 7 as they relate to allergic diseases and environmental toxins. To provide a balanced overview of infant health, the risk of transmission of infectious agents via human milk and the presence of drugs in human milk are also covered. In addition, there is brief mention of the development of obesity and atherosclerosis in later life in relation to the method of infant feeding.

Chapter 8 explores ways that maternal health can be influenced by lactation, with special emphasis on obesity, osteoporosis, and breast cancer, as well as the impact of lactation on ovulation and fertility. In Chapter 9, information from preceding chapters is synthesized in a discussion of ways to meet the nutrient needs of lactating women. Chapter 10 includes a brief review of recent research recommendations concerning lactation and breastfeeding and then presents the subcommittee's recommendations for research concerning nutrition during lactation. The conclusions and recommendations of the subcommittee are presented in the Summary, Chapter 1.

The subcommittee acknowledges the outstanding contribution of Carol Suitor, Study Director for this report. Her dedication, skill, and attention to all aspects of this report have been invaluable at all stages of its preparation.

The committee and subcommittee also appreciate the support provided by many other members of the Food and Nutrition Board staff, especially Dr. Alvin Lazen, Dr. Catherine Woteki, Mrs. Frances Peter, Dr. Yvonne Bronner, Ms. Marian Millstone, Ms. Wilhelmena Tamale, and Ms. Geraldine Kennedo. Mr. Michael Hayes ably served as copy editor.

The subcommittee benefited from advice and suggestions provided by

the Committee on Nutritional Status During Pregnancy and Lactation, from the sharing of information with the Subcommittee on Nutritional Status and Weight Gain During Pregnancy and the Subcommittee on Dietary Intake and Nutrient Supplements During Pregnancy, and from the assistance provided by the Food and Nutrition Board and its Subcommittee on the Tenth Edition of the Recommended Dietary Allowances.

Many people made important contributions to this combined report by giving presentations, providing the subcommittees with data or special written reports or analyses, sharing their views during workshops, commenting on drafts, or otherwise serving as resource persons. In particular, the committee and subcommittees wish to thank Dr. Thomas A. Arcury, University of Kentucky; Dr. Kenneth Brown, University of California, Davis; Ms. Becky Catey, Ross Laboratories; Dr. Catherine Cowell, Bureau of Nutrition, City of New York; Dr. Jan Dodds, Bureau of Nutrition, New York State; Dr. J. David Erickson, Centers for Disease Control; Ms. Linda Friedman, University of Rochester School of Medicine and Dentistry; Dr. Jean-Pierre Habicht, Cornell University; Dr. Suzanne Harris, Food and Consumer Services, U.S. Department of Agriculture (USDA); Mr. Jay Hirshman, Food and Nutrition Service, USDA; Ms. Patricia Jensen, Santa Clara County Department of Health, California; Ms. Lynn Kuba, Childbirth Educator, Fairfax County, Va.; Ms. Alice Lenihan, National Association of WIC (Supplemental Food Program for Women, Infants, and Children) Directors; Ms. Brenda Lisi, Food and Nutrition Service, USDA; Ms. Ruth Lubic, Maternity Center Association, New York City; Ms. Shelly Marks, Harbor University of California at Los Angeles Medical Center; Dr. Gilbert Martinez, Ross Laboratories; Dr. Margaret Neville, University of Colorado; Dr. Alan S. Ryan, Ross Laboratories; Dr. Rebecca Stoltzfus, Cornell University; Dr. Rita Thomas, Bristol-Myers; and Ms. Colette Zyrkowski, Centers for Disease Control.