Does L-Glutamine Break a Fast? – What the Research Says

Fasting has become increasingly popular for its potential health benefits, including weight loss, improved digestion, and enhanced mental clarity. 

In the midst of a fasting regimen, many individuals wonder if taking supplements like L-Glutamine can break their fast. 

This article will explore whether L-Glutamine interferes with fasting and if it’s a suitable supplement for those following a fasting protocol.

Will an L-Glutamine Supplement Break a Fast?

Yes, L-Glutamine supplementation will break a fast. While it is almost a non-caloric supplement, meaning it doesn’t pack as many calories as carbohydrates, proteins, or fats, it will still count.

For example, 5 grams of L-glutamine will be around 20 calories. So, that’s why it will break a fast.

Now, if you don’t consider 20-something calories breaking a fast, or if you’re not that strict, then you could say that L-glutamine won’t break a fast.

However, this only really applies if you’re fasting due to non-religious reasons.

If you’re really serious about fasting, then you should definitely avoid L-glutamine during fasting hours.

Now, I know what you’re thinking – there are other things to consider in this debate, like insulin spikes and breaking ketosis – but don’t worry, we’ll get to that in a second.

What Other Amino Acids Can Interfere with Fasting?

All amino acids can interfere with fasting. 

Branched-chain amino acids (BCAAs), for example, can break a fast due to their caloric content and potential to stimulate insulin production. After all, they are the building blocks of protein, and protein contains calories.

Therefore, if maintaining a strict fasting state is your goal, it’s essential to avoid supplements containing whey protein, BCAAs, or other amino acids with caloric content during your fasting window.

That said, it’s all about how strict you are with your fast.

Why Can L-Glutamine and Other Amino Acids Interfere with Fasting?

L-glutamine and other amino acids can interfere with fasting because they can trigger certain metabolic and hormonal responses that can disrupt the desired fasting state.

During fasting, the body goes through various physiological changes, which we’ll discuss in a second, but the general consensus on this particular issue is that the presence of amino acids can influence these changes and potentially negate some of the benefits of fasting.

Here are some reasons why L-Glutamine and other amino acids can interfere with fasting:

  • Amino acids can trigger insulin release: When amino acids are consumed, they can stimulate the release of insulin.
    Insulin is a hormone that regulates blood sugar levels and promotes nutrient storage in cells. [1]
    During fasting, one of the goals is to keep insulin levels low to promote fat burning and increase insulin sensitivity, which is not exactly possible if there are amino acids present.
  • Amino acids can disrupt ketosis: Fasting typically leads to a state of ketosis, where the body starts to break down fatty acids to produce ketone bodies for energy. [2]
    This occurs when glucose levels are low, and the body needs an alternative fuel source, which is why many people decide to fast.
    Anyway, consuming amino acids can/will provide an alternate energy source and suppress ketone production, thereby interfering with the ketosis process.
  • Amino acids can affect autophagy: Autophagy is a cellular process that helps to remove damaged or dysfunctional components within cells.
    It is an essential mechanism for maintaining cellular health and is believed to be upregulated during fasting.
    However, amino acids, particularly leucine, can inhibit the initiation of autophagy by activating the mTOR signaling pathway. [3] 

All that said, it is essential to note that the extent to which L-Glutamine and other amino acids interfere with fasting depends on the individual’s physiology, the specific amino acids consumed, and the quantity ingested

In some cases, consuming small amounts of amino acids may not significantly disrupt the fasting state, so once again, we come back to it – it’s all about how serious you are.

Will L-Glutamine Kick Me Out of Ketosis?

Small amounts of L-glutamine are unlikely to kick you out of ketosis. That said, it is still entirely possible for L-glutamine to do the opposite.

While it is an amino acid, it does not have a significant impact on blood sugar or insulin levels. 

However, consuming large amounts of L-glutamine may result in a conversion to glucose through a process called gluconeogenesis, which would probably affect ketosis.

As for the regular dose, 5-10 grams of glutamine, it probably won’t affect ketosis in any significant way, but still, this doesn’t have to be true for every person.

Is L-Glutamine a Carb?

L-glutamine is not a carb – it is an amino acid. There are 20 amino acids that make up proteins, and L-glutamine is one of them. 

To be more precise, glutamine is a conditionally essential amino acid, which means that if your body can’t produce enough L-Glutamine, you might need to obtain it from the diet or supplementation.

Carbohydrates, on the other hand, are a class of macronutrients that primarily provide energy to the body

They’re made up of carbon, hydrogen, and oxygen atoms and are classified as monosaccharides, disaccharides, and polysaccharides. [4]

Is it Ok to Take L-Glutamine on an Empty Stomach?

L-Glutamine can be taken on an empty stomach without any issues. In fact, most experts recommend taking L-Glutamine on an empty stomach to enhance its absorption and effectiveness. 

However, how true that is is up for debate.

What’s not up for debate is individual preferences and tolerance when taking supplements on an empty stomach. 

In other words, what works for someone may not necessarily work for you, and just because someone doesn’t experience any side effects doesn’t mean you won’t. 

That said, if you experience gastrointestinal discomfort or other side effects, adjust the timing and the dose accordingly.

Does L-Glutamine Spike Insulin?

L-Glutamine does spike insulin levels, however, not to a very great degree if you dose it correctly. [5]

Why does this matter?

Well, since L-glutamine has minimal (or at least not a significant) impact on insulin secretion, it is suitable for those on a “dirty fast”, as it should not disrupt the fasting state in any significant way.

What Supplements Won’t Interfere With Fasting?

Supplements that won’t interfere with fasting include non-caloric vitamins and minerals, electrolytes, and certain herbal supplements. 

Some popular examples that won’t interfere with fasting are multivitamins, fish oil, pure collagen, and creatine

These supplements do not provide energy or stimulate insulin production, making them suitable for consumption during fasting windows. 

Still, don’t take this at face value. You will still have to carefully read supplement labels and follow the specific guidelines of your fasting protocol to ensure you’re not inadvertently breaking your fast.


All in all, L-glutamine is generally safe to consume during fasting as long as you’re mindful of the dose and aren’t too strict with your process.

On the other hand, if you’re fasting for religious reasons or you absolutely want to make sure nothing interferes with your process – don’t consume glutamine during your fast.

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