**1. Introduction**

Globally, obesity rates remain high, and although incidence has plateaued in some countries (e.g., US men), rates of related comorbidities continue to escalate, such as, type II diabetes. Nutrition survey data suggest that populations are becoming overfed, yet undernourished, due to the poor nutrient density of the diet, contributing simultaneously to elevated rates of chronic disease and nutrient inadequacy. Meal replacements (MR)—a prepackaged, calorie‐ controlled product in a bar or powder mix that can be made into a shake or beverage—have long been validated as safe and effective tools for weight loss (and weight maintenance). More recent studies have indicated that high‐protein MR are also effective at maintaining lean body

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

mass and reducing visceral body fat during weight loss. This review focuses on MR that do not require medical supervision (those classified as medical foods).

Depending on the formulation, MR also possess the advantage of having a low glycemic index (GI) value; low‐GI diets have been linked to improved weight maintenance and reduction in risk of diabetes and ocular disease. Many nutrition researchers and authoritative bodies around the world have highlighted the need to improve the nutrient density of diets as a means to reduce obesity while maintaining optimal nutrition status. MR also tend to be nutrient dense, meaning that they possess a high ratio of essential nutrients relative to calories.

Some markets have established clear regulatory standards and definitions for the composition and marketing claims for MR (e.g., Codex, Canada, EU, Brazil, Korea, Indonesia). However, several large markets (e.g., US, Mexico, China, Russia, India) still lack these important standards, in turn limiting research opportunities and recognition by governments, healthcare professionals and consumers of the value the category provides.

The aim of this chapter is to review the extensive body of literature validating the safety and effectiveness of MR as weight loss and weight maintenance tools; explore the benefits of MR beyond weight loss, including maintenance of lean body mass and low glycemic index; discuss the concept of nutrient density, its importance in nutrition and how MR fit into a nutrient‐dense diet; and discuss the need for regulatory standards to be established in those countries that currently lack a definition for MR.
