L-leucine is an amino acid. These are the building blocks of protein, with each protein having its own unique amino acid makeup and combination.

L-leucine featured image

There are twenty amino acids in total. L-leucine is part of a select group, however – alongside isoleucine and valine, it’s a branched chain amino acid (a BCAA). BCAAs give you energy during intense physical effort – for instance, during training.

L-leucine is also one of nine essential amino acids. These are amino acids that the human body can’t produce by itself. They need to be taken in exogenously – you need to get them from food and supplementation.

But why does all this matter? What does l-leucine have to do with you and your training?

L-leucine and the Human Body

Amino acids each play plenty of different roles, though most of these revolve around the creation of protein.

Muscle mass and healing

L-leucine is no different. As a key, essential amino acid, you need to eat plenty in order to bolster muscle growth and maintenance.

In fact, leucine is a good tool for recovery in general. It can help to increase muscle size and maintain good lean body mass, which is why you’ll often see athletes, particularly physique athletes like bodybuilders, taking it in large quantities. It may also help to heal skin and bones, making it good for getting over any injury or surgery. 

healing from injury

There is mixed data on many of leucine’s effects on the human body. However, one of the more consistent findings suggests that it can slow down age-related muscle loss, or sarcopenia.

Research suggests that supplementing with leucine can help to maintain lean mass as we age, as well as keeping a healthy body composition (the ratio of lean body mass to fat), especially in those genetically predisposed to sarcopenia.

This compounds with its use for healing. In fact, supplementing with leucine, especially during otherwise suboptimal intake of protein, has been shown to offset anabolic resistance, which can cause a deterioration in skeletal muscle mass.

We typically begin to lose around 3-8% of our muscle mass per decade after thirty, with this rate picking up even more after sixty, so leucine may be very welcome indeed as we age.

Blood sugar levels

It isn’t all about gaining or maintaining muscle, though. Leucine has more to give.

blood sugar testing

It can help with blood sugar regulation, according to recent data. When taken with glucose, it can significantly reduce blood glucose responses, for example, whilst also boosting insulin production. It manages this through its interaction with pancreatic β cells, body fat, the liver, and muscle mass – proving itself central to healthy blood glucose regulation.

This may make it perfect for managing conditions such as diabetes.

However, this doesn’t necessarily mean that throwing back a bit of extra l-leucine will balance your blood sugar out. No supplement can make up for an inappropriate diet, nor will one be able to match the benefits of a healthy diet.

The best way to manage blood sugar levels is to eat a varied, balanced diet, rich in complex carbs, fiber, healthy fats, and lean proteins. These will combine well with l-leucine to fully stabilize blood sugar levels.

If you’re concerned about your blood sugar levels or diabetes, it’s always best to talk to your healthcare provider. They will be able to fully advise you on diet, lifestyle, and any medical intervention that may be needed.

Hormone balance and production

There is a strong link between leucine and human growth hormone (HGH). This can be critical for athletes and those looking to overcome conditions like sarcopenia, as well as any children or adolescents looking to make their development as healthy as possible.

L-leucine profile

HGH does what it says on the tin – it helps the human body to grow. It lies behind childhood and adolescent growth and development. Throughout life, it works to maintain your body’s tissues and organs. In an athletic context, it enables hypertrophy (muscle growth) and further adaptations.

Optimising leucine intake can therefore contribute to healthy growth.

We also begin to see lower HGH output as we age. Our pituitary glands produce less and less of it as we reach middle age and beyond.

Leucine therefore serves a few purposes as we age – helping us to maintain muscle growth, partly through improving our HGH output, all whilst balancing blood sugar and helping us to maintain healthy body composition, making us far less likely to suffer from a host of chronic conditions such as diabetes.

There is also a possible link between leucine and testosterone production. Though there are mixed data on this, with some studies showing a link and others not, it makes sense. If nothing else, improving muscle mass and HGH output will directly influence your testosterone levels, thus boosting them.

Weight management

We’ve mentioned muscle mass, lean mass, and body composition above. Leucine can help with all. Specifically, it can help you to lose weight. There is a limited yet growing body of research showing how critical leucine can be for your body’s metabolic processes – for instance, as above, its role in stabilizing your blood glucose levels.

This opens up leucine as a very interesting weight loss ally. Optimal levels help to optimize your metabolic processes. Combine this with the fact that dietary leucine intake is linked with maintenance of muscle mass during a calorie deficit, and with HGH and muscle growth more generally, and it begins to look really quite potent.

Don’t run away with this. There is no consensus on dosing leucine for weight loss. It also won’t be the deciding factor in any weight loss program. A healthy diet allowing for a calorie deficit and paired with an active lifestyle will do more for weight loss than anything else, all things being equal. However, leucine does seem to show promise as a great aid to this process.

The Downsides of L-leucine

Not everyone is rosy with leucine, however – or, at least, it isn’t an unqualified good. There are a couple of potential side effects to look out for with a leucine supplement (hence it’s always better to get as much nutrition as possible from whole food sources).

These effects can include:

  • Unbalanced nitrogen levels, as a singular amino acid causes a negative nitrogen balance. This can impair your metabolic function and place undue and potentially damaging stress on your renal system (your kidneys, ureters, and urethra).
  • Hypoglycemia, or dangerously low blood sugar levels, as the leucine depresses levels too much.
  • Pellagra, or depleted niacin (vitamin B3 levels) which can lead to symptoms such as hair loss, skin lesions, and gastrointestinal concerns.

You should be wary of using supplements to replace whole foods. As their name suggests, they are there to supplement. A little can go a long way. The rest should come from dietary sources – whole foods rich in amino acids, with enough focus on leucine to give you the bulk of your recommended intake.

If you’re unsure about taking any new supplement, or if you experience any side effects, consult your healthcare professional. Always consider speaking to your doctor before making any drastic lifestyle or dietary changes.​

Dietary Sources of Leucine

With this in mind, what exactly should you be eating to lay a good foundation for your leucine intake? Luckily, there are plenty of common food sources rich in it. Though you will find small amounts in plant-based sources, leucine is generally seen in larger quantities in animal products.

Sources of leucine include:

  • Salmon, which will also bring you a generous helping of omega-3 fatty acids. If you can, try to go for wild-caught salmon as there are some safety and health concerns surrounding farmed fish.
  • Beef, one of the best sources of amino acids going, is rich in large quantities of leucine. For a fuller range of nutrients, and thus health benefits, consider buying grass-fed beef if you can.
  • Chickpeas, which represent a great vegan source of leucine. They are pretty great, actually – half a cup gives you 7 g of mixed protein, as well as 6 g of dietary fiber. Eat them in humous, stews, curries, soups, salads, or dry roasted as snacks on their own.
  • Brown rice, another vegan source, will give you some leucine. It’s also got a bit more bite, a bit more texture, than white rice, making it a real treat.
  • Eggs, one of the best sources of protein going, are a complete protein source. This means that they contain all 20 amino acids, including leucine – this is rare for a vegetarian staple.
  • Soybeans give you a little, too, and can be enjoyed in plenty of different ways – tempeh, tofu, edamame, or simply roasted on their own. Soybeans make a great meat substitute in many dishes.
  • Nuts, which give you plenty of fat and protein. In particular, almonds, Brazil nuts, and cashews are great sources (as are peanuts, even if technically they are legumes!)