The most abundant amino acid in the body, offered here as a simple unflavoured powder from ethical brand Viridian. It is popular with active people, those doing regular training, and customers who like to include glutamine in their daily routine alongside a balanced diet.

The 100g tub contains pure L-glutamine produced by microbial fermentation, with no artificial fillers, sweeteners or additives of any kind, and it is suitable for vegans. A level teaspoon (3.5g) mixed into water or juice is the usual daily serving; for best results take it away from protein-containing meals, ideally 30 to 60 minutes before or after eating. Not recommended during pregnancy or breastfeeding unless advised by your healthcare practitioner. Like the rest of the Viridian range, it comes from an independent company that gives a share of its profits to charity.