Diagnosing undernutrition children and adults: new French criteria. Why, for what and for whom? A joint statement of the French National Authority for Health and French Federation of Nutrition.

The objective was to establish new diagnostic criteria for undernutrition for the French population, concordant for children aged <18 years and adults aged <70 years, easy to use by health professionals and applicable whatever the situation (in and outpatients). A multi-disciplinary working and a reading group were involved. The procedure was divided into four phases: (1) systematic review and synthesis of the literature; (2) writing of the initial version of the guidelines; (3) reading and (4) finalisation. The literature search included international guidelines, meta-analyses, systematic reviews and randomised control trials from January 2007 to 31 July 2018. A two-step approach was selected: diagnosing undernutrition and then grading its severity. For diagnosis at least one phenotypic criterion associated with at least one aetiologic criterion were required for both children and adults. Phenotypic criteria for children were weight loss, Body Mass Index (BMI) < International Obesity Task Force curve 18·5, weight stagnation, reduction of muscle mass/function; for adults: weight loss, BMI < 18·5 and reduction of muscle mass/function. Aetiological criteria for children and adults were reduction in dietary intake, reduced absorption and hypercatabolism. Phenotypic metrics were used in both children and adults for grading severity (moderate or severe). These new French recommendations integrate the proposals of recent international recommendations combining aetiologic with phenotypic criteria, but for the first time, they are concordant for children and adults. The WHO threshold of 18·5 for BMI was kept as phenotypic criteria because epidemiological data show an increased mortality for that threshold.