Does L-Tyrosine Break A Fast? What The Science Says

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With the popularity of supplements like L-Tyrosine, there’s confusion around what breaks a fast and what doesn’t.

As a dietitian, here’s my quick answer:

L-Tyrosine by itself blended with water will not break a fast because it is a free-form amino acid, which won’t kickstart insulin secretion.

However, L-Tyrosine mixed with sugary products or added to a flavored pre-workout supplement will likely break a fast (more on this below).

Key Takeaways

  • Taking L-Tyrosine 30-60 minutes before exercise (or before a stressful event), whether in a fasted state or during a feeding window, can help with focus and concentration.
  • L-Tyrosine is safe to take on an empty stomach, although some people might experience digestive upset, depending on the dose taken (no optimal dose has been established so far in the literature).
  • Opt for a product that’s only ingredient is tyrosine to ensure you’re getting a higher quality product that won’t break a fast.

Will L-Tyrosine Break Your Fast?

Fasting is generally defined as abstaining from food and beverages that contain calories, with the purpose of avoiding an insulin response.

As L-tyrosine is an amino acid that does not contain a significant number of calories it will not break your fast.

That said, if you take a flavored L-Tyrosine supplement that contains additional ingredients (added sugar or sweeteners for example), and/or you mix it with a caloric drink, then it will break your fast. 

Here are some examples of L-Tyrosine supplements:

  • Pure, Unflavored L-Tyrosine. 100% L-Tyrosine Powder from MyProtein, only contains one ingredient (L-Tyrosine), and since the unflavored version has no caloric content from added sugars, nor sweeteners, it does not affect insulin secretion.

    Therefore, taking this type of L-Tyrosine supplement (mixed with water) will not break your fast.

The active ingredients in this stack are caffeine, Beta-Alanine, Citrulline, and L-Tyrosine.

Even if a stack has been sweetened with artificial sweeteners (such as aspartame, saccharin, and sucralose that contain no calories), it might still impact your fast, since some studies have shown that zero-calorie sweeteners impact blood sugars and insulin secretion. 

However, the research around zero-calorie sweeteners is inconclusive, since some evidence suggests that these cause a rise in blood sugars (despite not containing carbs and calories) and others suggest the contrary. 

This is also a controversial topic for diabetes since some sweeteners are advertised as healthy alternatives for those managing diabetes. 

Having said this, if you want to be sure not to break your fast, my advice would be to avoid taking flavored L-Tyrosine that might contain sweeteners.

Similarly, if you took pure L-Tyrosine and mixed it with juice or your usual whey protein shake, it would also break your fast, since the juice and protein shake used to mix it contains calories.

Is It Safe To Take L-Tyrosine on an Empty Stomach?

L-Tyrosine is safe to take on an empty stomach. Taking it on an empty stomach can actually help with its absorption as it is not competing with other nutrients for absorption. 

However, some people may experience gastrointestinal discomfort, such as digestive upset when taking L-Tyrosine on an empty stomach but this depends on the dose and the individual’s digestive system.

To minimize the risk of gastrointestinal discomfort, it might be worth starting with a lower dose of L-Tyrosine and gradually increasing the dosage over time. 

For example, 200 mg as the starting dose for a few days, and gradually moving up to 500 mg if 200 mg is tolerated.

If the above does not work, another option would be to wait until the feeding window to take L-Tyrosine, either with a small meal/snack or 30-60 minutes after a small meal/snack. 

Should You Take L-Tyrosine When Fasting or During a Feeding Window?

The decision to take L-Tyrosine while fasting or during a feeding window depends on your goals and whether you tolerate it in a fasted state and on an empty stomach.

If your goal is to workout in a fasted state (e.g. if you train in the morning before your first meal), then taking the pure L-Tyrosine version will not interfere with your fast.

If you workout during your feeding window (e.g. if you train in the evening), then it may be beneficial to wait 2 hours after a meal/snack for better absorption.

For example, if you train at 7 pm, make sure you finish eating by 4:30 pm and you have your L-Tyrosine (unflavored, flavored, or in a stack) 30 minutes before your workout, at around 6:30 pm.

However, if you experience stomach upset on an empty stomach or in a fasted state, then you can take a serving of L-Tyrosine during a feeding window with a small snack.

For example, you could have a slice of white bread and jam 60 minutes before a workout, and take the supplement 30 minutes before a workout with a glass of juice.

How to Take L-Tyrosine Without Breaking a Fast

To avoid breaking a fast, ensure you have the unflavoured version of pure L-Tyrosine because the nutritional values of flavored versions vary and it’s unclear whether sweeteners will break your fast or not. 

Additionally, to avoid breaking your fast I recommend mixing it with water (if taken in powder form) or taking it with water (if taken in pill form) rather than other beverages.

When it comes to dosage, the evidence is fairly limited for the optimal dose of L-Tyrosine, since the doses given in different studies range from 500 mg to 12 g daily (or up to 200 mg/kg daily).

For example, one study investigated the use of 100 mg/kg (i.e. if you weigh 55 kg or 121 lbs, this is 5.5 g) of tyrosine in human subjects during a 4.5 hour exposure to cold and hypoxia (a state in which oxygen is not sufficient). 

Results showed that tyrosine significantly decreased symptoms, adverse moods, and performance impairments in those who were greatly impacted by these extreme conditions. 

Despite these different ranges, a dose of 500mg – 1g daily might be enough to show some benefits in focus and alertness, even though its direct benefits on exercise performance remain inconclusive.

As a general guideline, add 500mg of unflavoured (pure) L-Tyrosine powder to water around 30-60 minutes before exercise. This will allow your body to metabolize it in time for your workout, without breaking your fast.

My personal favorite L-Tyrosine supplements are 100% L-Tyrosine powder from either Myprotein or BulkSupplements (for me, it just depends which one is cheaper at the time of purchasing).

Both offer a pure version that is free from additives (artificial sweeteners, flavorings, and preservatives) and easy to blend.

What Other Supplements Can Break a Fast?

About The Author

Giulia Rossetto

Giulia Rossetto is a qualified Dietitian and Nutritionist. She holds a Masters in Human Nutrition (University of Sheffield, UK) and more recently graduated as a Dietitian (University of Malta). Giulia aims to translate evidence-based science to the public through teaching and writing content. She has worked 4+ years in clinical settings and has also published articles in academic journals. She is into running, swimming and weight lifting, and enjoys spending time in the mountains (she has a soft spot for hiking and skiing in the Italian Dolomites).

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