L-Aspartic Acid: Benefits, Side Effects, Best Time to Take It & More

L-Aspartic Acid

(Aspartate)

Evidence: Reasonable
Possible Benefits: Reasonable
Safety: High

What is L-aspartic acid?

L-aspartic acid is a non-essential amino acid. As a supplement, it is often used for increasing testosterone levels and improving fertility in men. This article is about the main benefits of L-aspartic acid, its potential side effects, the best time to take it, and more.

What does L-aspartic acid do for the body?

Since L-aspartic acid is a non-essential amino acid, you do not need to consume it to survive. However, this amino acid still plays an important role in human health.

Just like D-aspartic acid, L-aspartic acid is a regulator of testosterone synthesis. It works in the central brain region to cause a release of hormones, such as luteinizing hormone, follicle-stimulating hormone, and growth hormone.

Besides this, L-aspartic acid has many additional functions in the body. It is necessary for removing toxins from the cells, proper immune function, producing ATP and glucose, improving memory and cognition, and more.

Possible benefits

All of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.

Major benefits

Improved fertility – One study on infertile men found that 26.6% of subjects became fertile over 90 days of taking D-aspartic acid. In these men, sperm count and seminal mobility were increased by 50-100% and luteinizing hormone was increased by 30-60%. This effect likely applies to L-aspartic acid as well but to a smaller extent.

Minor benefits

Increased testosterone levels – D-aspartic acid (and probably L-aspartic acid as well) can improve testosterone levels by about 30-60%. This effect can be long-lasting in infertile men. However, testosterone levels usually go back to baseline after 6-12 days of supplementation in men with normal fertility and testosterone levels. In healthy men who do resistance training, aspartic acid can decrease the amount of free and total testosterone.

Possible side effects

These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.

Increased cholesterol levels
Reduced testosterone – While the supplement can increase testosterone levels in infertile men, in healthy men who do resistance training, L-aspartic acid can actually decrease the amount of free and total testosterone.
Amino acid imbalance – Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Toxicity – While acute toxicity is extremely rare, taking high amounts of L-aspartic acid could lead to chronic toxicity and cause some health problems. To prevent chronic toxicity, it is best to stay below 3 grams a day unless you have a great reason to take more.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.

Who should not take L-aspartic acid?

You should probably avoid taking the supplement if you:

get enough aspartic acid from food
experience a severe adverse reaction after taking the amino acid
are a woman
are on a tight supplement budget (since there are more cost-effective supplements on the market for most people)

Who will benefit the most?

You should consider taking the supplement if you:

are infertile or wish to improve fertility
have low total testosterone
consume very little protein (less than 0.3 grams/pound of body weight)

How much L-aspartic acid should you take?

Since aspartic acid can be found in food or synthesized in the body, you may already get sufficient amounts without taking it as a supplement. About 0.36 grams of protein/pound of body weight should generally be enough to prevent any symptom deficiency.

If you plan to take L-aspartic acid as a supplement, 2 grams appears to be the best daily target for most people. This amount should provide most of the benefits without meaningful side effects.

Some people may benefit from doses higher than 2 grams. These include infertile men and men with low testosterone.

The upper safety limit for L-aspartic acid is not well-established. To stay on the safe side, don’t take more than 3 grams daily unless you have a great reason to do so. Higher amounts may cause problems if you take the supplement for a prolonged period.

Food sources of aspartic acid

Aspartic acid is found in all whole foods that contain dietary protein.

The amount of aspartic acid per gram of protein varies from food to food but a general rule of thumb is that the more protein you eat, the more aspartic acid you are getting from food.

The easiest way to find out exactly how much aspartic acid or other amino acids you are getting from food is with Cronometer.com. This free app allows you to track all vitamins, minerals, and more.

Best time to take L-aspartic acid

Like most other amino acids, L-aspartic acid is water-soluble, so you don’t have to take it with food to absorb it well. Taking the supplement with food is better if it causes stomach upset when you take it on an empty stomach.

Whether you take the supplement in the morning or the evening doesn’t matter much. It should not interrupt your sleep in any way.

If you practice time-restricted eating, take this amino acid during your eating window to guarantee it won’t break your fast.

Unless it feels too impractical, spread the daily dose into 2+ smaller doses throughout the day.

Interactions

L-ornithine
Combining ornithine and aspartic acid can improve brain function in people with advanced liver disease. It may also be effective at reducing levels of a toxic chemical called ammonia in the blood.
Other amino acids
Essential and non-essential amino acids should be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects if there isn’t enough of another amino acid. For example, this principle applies to glycine and methionine, lysine and arginine, and the BCAA trio. There are many other proven and unproven examples. Food or a protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.

Where to buy L-aspartic acid

Amazon is the best option for ordering aspartic acid supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.

Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.

L-aspartic acid vs. D-aspartic acid

Aspartic acid has 2 forms: L-aspartic acid and D-aspartic acid.

These forms are distinct from each other and have very different effects on the body.

D-aspartic acid helps produce and regulate sex hormones, such as testosterone.

L-aspartic acid has a wide variety of functions in the body, ranging from energy production to immune function to the removal of toxins.

FAQ

You can take the amino acid daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it daily. Not taking the supplement every once in a while could lead to better absorption. That is yet to be proven or disproven.

All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatin, which rarely comes from an ethical source.

Yes. Most amino acids, including L-aspartic acid, absorb and digest well if you take them before falling asleep. The supplement should not impact sleep quality in any significant way.

This amino acid should not become harmful once it exceeds the expiration date but can lose potency over time.

Keep the supplement in a cold, dark, and dry place, and it should remain just as potent for many months or even years.

While toxicity is rare, too much L-aspartic acid in the system can cause some health problems. It is best to stay below 3 grams a day to prevent these side effects.

You may need more of this amino acid if you:
– are infertile or wish to improve fertility
– have low total testosterone
– eat very little protein (less than 0.3 grams/pound of body weight)

You should notice the benefits within a week of supplementation. The increases in testosterone usually vanish in healthy adults after 6-12 days but can persist in infertile men or people with low testosterone.

You can easily find vegan-friendly L-aspartic acid pills and powders but always check the label to be sure. If you buy the amino acid in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.

Like most other amino acids, aspartic acid is water-soluble, so you don’t have to take it with food to absorb it well.

L-aspartic acid should not break a fast unless you take a very high dose at once. If you practice time-restricted eating, take this amino acid during your eating window so it doesn’t break your fast.

References

Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.

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