Glutamine--from conditionally essential to totally dispensable?

Recently a large multicentre randomised controlled trial in critically ill patients reported harm to the patients given supplementary glutamine. In the original publication, no explanation was offered for why this result was obtained; a large number of studies have reported beneficial effects or no effect, but never before reported harm. These results have been commented upon in a number of communications. Now some of the authors of the multicentre randomised controlled trial present a review and meta-analysis of glutamine supplementation, and the discrepancy of results is suggested to relate to intravenous administration to patients of supplementary glutamine via parenteral nutrition or a combination of enteral and parenteral nutrition in contrast to enteral administration of supplementation or a combination of enteral and parenteral supplementation. To explain results by epidemiological means only, by combining results into a meta-analysis, is perhaps not the best way to explain mechanisms behind results. Meta-analyses are primarily hypothesis generating. Launching treatment without a solid mechanistic explanation is always risky. Glutamine supplementation of the critically ill comes into that category. Now we will all have to do our homework and try to understand whether supplementation or omission of glutamine for patients fed parenterally is a good idea or not.