Glutamine isn't an essential amino acid, but in certain circumstances, like illness or heavy exercise, your glutamine stores may be low and you may benefit from supplementation. You don't necessarily need to take glutamine on an empty stomach, however, to make sure it works. Consult your health care provider before adding glutamine to your daily regimen.
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When to Take it on an Empty Stomach
A 2004 article published in The Austin Chronicle says you should take glutamine on an empty stomach if you're using it for reasons other than musclebuilding, which might include digestion and immune system health. The rationale to take it without food is because you need less of it and may tolerate the supplement better without food.
When to Take it with Food
When you're taking glutamine for bodybuilding you're likely taking it in large amounts and may have an easier time tolerating the supplement when it's taken with food, says The Austin Chronicle. Plus, the amino acid combines with the other amino acids in the food you eat to help build muscle. The University of Maryland Medical Center notes that glutamine can be taken with drinks or food at room temperature, but should not be combined with hot liquids.