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With the number of individuals becoming overweight or obese, health care professionals are in need of accurate, reliable, and convenient tools to help personalize weight-loss programs. Recently, a new handheld indirect calorimeter (i.e., MedGem/BodyGem; also know as "Gem") was introduced as a convenient way to assess resting metabolic rate (RMR) to determine daily energy needs. Several validation and comparison studies were conducted to determine whether the Gem device is accurate and reliable, and results from these studies are mixed. Fourteen human studies (12 adult, 2 pediatric) were conducted, and 12 met the established criteria for this review. In all Douglas-bag (DB; n = 4) validation studies, the Gem device was not significantly different than the DB (mean difference adult ±1%, pediatric ±1%). The intraclass reliability of the Gem ranged from 0.97 to 0.98, and the interclass reliability to the DB ranged from 0.91 to 0.97. Although few (n = 2) studies have demonstrated that the Gem device measures RMR significantly lower (-8.2% to 15.1%) than traditional metabolic carts, it performs very comparably (RMR values 0.1-4.0%, interclass reliability 0.76-0.92) to traditional metabolic carts in most (n = 6) of the comparison studies. Based on these data, the Gem device is a valid and reliable indirect calorimeter for energy assessment in most adults and children.

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