INTRODUCTION

Vegetarian diets are becoming increasingly popular [1-6]. A nationally representative study conducted in the United States in 2008 estimated that 10 percent (22.8 million) of Americans aged 18 and older follow a "vegetarian-inclined" diet, 3.2 percent (7.3 million) indicated that they follow a vegetarian diet, and 0.5 percent (1 million) follow a vegan diet [7]. A poll conducted in the US in 2006 estimated that 6.7 percent of Americans aged 18 and older do not eat meat, 2.3 percent do not eat meat, fish, or poultry, and 1.4 percent do not eat meat, fish, poultry, dairy products, or eggs [1]. Approximately 5 percent of individuals in the United Kingdom, Germany, and Australia describe themselves as vegetarian [8-10].

An increasing number of families are choosing to rear their children on a vegetarian eating style [11,12]. An estimated 8 percent of adolescents in the United Kingdom [13] and 6 percent of public middle- and high-school students surveyed in the midwestern United States [14] consume a vegetarian diet. A poll conducted in 2005 estimated that 6 percent of American youth aged 8 to 18 years do not eat meat, 3 percent do not eat meat, fish, or poultry, and 1 percent do not eat meat, fish, poultry, dairy or eggs [15].

Studies of vegetarian diets are complicated by variations in definitions for the term "vegetarian". Definitions range from whether the individual considers himself or herself as vegetarian ("self-defined" vegetarians), avoids meat only, or lives by the strict definition (never consuming meat, fish, and poultry). As an example, one review of dietary patterns and nutrient intakes of self-defined vegetarians (aged six years and older) found that patterns ranged from those who consumed reduced amounts of red meat but included poultry and fish, to those who excluded all animal foods [16].

Reasons for choosing a vegetarian diet are varied and include potential health benefits and sociopolitical, ecological, and ethical issues related to allocation of resources and animal rights [3,7,17-21]. Adolescents pose a particular challenge because it may be difficult to determine if an adolescent's choice to become a vegetarian is related to dietary restriction [22,23]. The types and composition of vegetarian diets also are varied and have important implications for the growth and development of children and adolescents.

The nutritional quality of vegetarian diets and strategies to prevent nutritional deficiencies while consuming vegetarian diets are reviewed here. Nutrition requirements, deficiencies, and supplementation of specific nutrients are discussed separately. (See appropriate topic reviews).