Why Take L-Glutamine on an Empty Stomach?

Taking L-glutamine on an empty stomach before bed can help with weight loss, according to ISSA.
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Glutamine is key to building muscle and is also the most abundant amino acid in the human body, according to the Memorial Sloan Kettering Cancer Center. Getting too little can cause your muscles to deteriorate, but how you supplement with L-glutamine can affect how well your body uses the compound.


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Taking L-glutamine on an empty stomach before bed can help with weight loss, according to ISSA.

Know L-Glutamine's Role

The human body makes glutamine, but we also get it through foods in our diet, such as meat, eggs, grains and dairy, according to a June 2019 scientific review of glutamine synthesis studies published by MDPI Cancers​. L-glutamine acts to convert amino acids into protein, to fuel muscle growth. It's also vital for other biological functions in the body, including maintaining the integrity of bodily tissues. This makes the supplement helpful for fitness and healthcare applications.


Read more:BCCA vs. Protein Powder

Athletes and bodybuilders use L-glutamine supplements to put on muscle and lose fat. According to ISSA, L-glutamine and other amino acids work together to act as building blocks for connective tissues in skin and joints, and are critical to supporting the body during training and exercise.


This amino acid helps regulate and produce energy, blood sugar and immune function, as well. Hormone and neurotransmitter synthesis, mineral absorption and nerve cell protection are other vital roles that L-glutamine assists.

A deficiency of glutamine can cause you to be more susceptible to infectious diseases. It can also contribute to a higher propensity for metabolic disorders, according to Texas A&M University.


People deficient in protein — such as those who are not taking in enough, based on their amount of exercise, or vegans who are not successfully getting enough complete proteins — are most at risk. Older adults can also be at risk as well as those with kidney or liver disease, according to a September 2019 study published in ​Translational Medicine of Aging​.

Animal protein contains the most balanced levels of all amino acids needed for optimal functioning of the human body, according to Texas A&M University. Beef, for example, contains 63 to 68 percent protein, where vegetable sources include 12 percent on average. Animal sources contain complete proteins, but plant sources must be carefully combined for complete protein, as most are deficient in multiple amino acids.

If you are getting adequate protein, supplementing with L-glutamine can further your fitness goal. It can help the body produce more energy to fuel muscle, without storing it as fat, according to ISSA.

Stimulate L-Glutamine Weight Loss

L-glutamine can also help you lose weight, according to ISSA. One reason for L-glutamine weight loss is that the body can convert it to glucose, to fuel muscles, without triggering the body's fat-storing hormones. One great L-glutamine side effect is that you'll feel fewer cravings for sugar or alcohol, according to ISSA.

Read more:How Much L-Glutamine Should I Take Daily?

ISSA recommends taking the amino on an empty stomach before bed, for maximum fat-burning and weight loss. L-glutamine works in conjunction with two other amino acids — methionine and arginine — to ramp up the body's production of somatropin while you sleep. Somatropin is a growth hormone that helps oxidize fat and promote muscle growth and is made mostly during the time that you're asleep.

Arginine is a non-essential amino acid, meaning that the human body can make its own. However, the body must ingest methionine from the diet. Animal proteins such as meat, eggs and dairy are good sources, according to Texas A&M University. Getting sufficient methionine from a plant-based diet can be trickier, as rice, wheat, corn and soy can convert to sugar in the body and get stored as fat.

Understand L-Glutamine Side Effects

Whether you prefer to supplement L-glutamine with or without food, it helps you recover faster after a workout or during times of illness or physical stress. However, you shouldn't take it long-term, in amounts above 40 grams per day, according to a May 2019 review of studies published in MDPI Nutrients.

Too much L-glutamine, with or without food, increases ammonia in your system and can prevent your body's detoxification process. It also competes for absorption with other amino acids, creating an imbalance of amino acids in your bloodstream. Too much L-glutamine in your system, over time, can also feed cancer cells, setting the stage for them to reproduce, according to a May 2019 review of studies published in ​MDPI Cancers​.

Read more:The Best Foods to Eat if You Have Cancer

Taking glutamine is unlikely to cause a reaction, according to the University of Michigan. The university recommends only taking glutamine capsules on an empty stomach, however. When taking glutamine capsules, wait at least two hours after eating or take the pills at least one hour before your meal.

When using powder, the university advises mixing it with liquid or soft food such as apple sauce, yogurt or pudding. Don't let it sit in the refrigerator, but instead eat it right away.

Call your doctor if you have chest pains, nausea, dizziness or any other unusual L-glutamine side effects after taking the supplement. Less-severe side effects can include a headache, stomach upset, swelling or fever, according to Memorial Sloan Kettering Cancer Center.

A better choice than supplementing with one amino acid is to take a supplement that includes all of the essential amino acids, as well as glutamine, recommends ISSA. Leucine, a branched-chain essential amino acid (BCCA), is potentially the most important for muscle growth. Isoleucine and valine are other BCCAs favored for muscle building. For best results, get a supplement that includes all nine essential amino acids, with extra leucine and glutamine, according to ISSA.

The University of Michigan recommends talking to your physician before supplementing with glutamine, particularly if you have liver or kidney disease. If you're pregnant or nursing a baby, make sure to get your doctor's guidance, as it isn't known how glutamine could affect an unborn or breastfeeding child. Your doctor might recommend frequent blood or urine tests while you're on the supplement, to ensure you're not harming your body.