Systematic reviews: how the Academy of Nutrition and Dietetics of the United States formalized criteria to evaluate the weight of evidence on the application and safety of umami-contributing ingredients

The discovery of the umami taste and the molecules involved in its perception triggered a movement within the scientific community aimed at studying every detail concerning both physiological processes and safety aspects.

When typing the word “umami” or “glutamate” into databases such as Scopus or Science Direct, for example, thousands of related articles can be found. However, to disseminate scientific information to the community, caution and research expertise are required.

To promote topics related to nutrition, the American Academy of Nutrition and Dietetics created a virtual library called the EAL (Evidence Analysis Library). On this site, experts synthesize the most important and relevant scientific information regarding nutrition and dietetics practice, using a methodology to conduct transparent and objective meta-analyses, making the information accessible to both professionals in the field and the general population.

This methodology involves five stages:

• Stage 1: Question formulation – Defining a specific area and a hypothesis to attempt to conclude or recommend something. This includes types of patients, special needs of the population, possible alternatives, and outcomes of greatest interest.
• Stage 2: Collecting and classifying articles of interest – Conducting a systematic literature review to identify evidence, gathering the articles, and classifying them by type of evidence. This classification distinguishes preliminary articles from new findings according to study design. The Academy organizes them into a spreadsheet and classifies them as A, B, C, D, M, R, or X.
• Stage 3: Critical appraisal of each article – Critically assessing the scientific validity of the articles and establishing quality criteria, which are entered into a spreadsheet with symbols (+, -, Ø, NA) to designate whether the article is positive, negative, neutral, or not valid.
• Stage 4: Evidence summary in narrative form with general tabulation – Combining the findings of all documents into a “summary of evidence” and/or “general table” that synthesizes the relevance of the information and allows comparisons among articles.
• Stage 5: Development of conclusions / strength of evidence – To reach a concise conclusion (an answer to the question), the synthesis of relevant study information, their class, and quality are considered. A “grade” is assigned to indicate the strength or weakness of the evidence: Grades I, II, and III (strong, fair, weak), Grade IV (expert opinion only), and Grade V (no evidence available to support or refute the question).

The umami-related question was based on whether this taste could improve the acceptability of foods, for example, with reduced sodium content, without sacrificing flavor, as well as the safety of industrially produced umami substances (mainly monosodium glutamate).

The purpose of the systematic review was to help dietetic experts understand umami and monosodium glutamate from both a scientific and culinary perspective.

The evidence analysis made it possible to discuss that umami and industrially produced substances providing this taste are not very palatable when consumed pure, just like salt and other ingredients. However, when added to foods, they can enhance flavor. For these reasons, it is important to have dietary variety so that the senses are exposed to a wide range of flavors in different foods and can appreciate them, even with reduced sodium levels.

Regarding safety, analyses of studies classified as Grade II showed contradictory results on the presence of side effects after monosodium glutamate intake by healthy adults, leading to the hypothesis that such manifestations may not be related to the substance. Furthermore, risk assessments carried out by the FDA (Food and Drug Administration) concluded that umami-providing ingredients are safe for human consumption when used according to technological recommendations.

The full report and research summaries are available in English at: http://andevidencelibrary.com/topic.cfm?cat=4818, where the complete analysis and details of the process can be accessed.