Supplements›Protein, amino acids & fitness

BCAAs: are they safe to take? What to watch for

BCAAs are three amino acids your body uses to build muscle. To get more out of your workouts, take them before or after exercise. But taking high-dose supplements for a long time may strain your liver and kidneys, and it's best to avoid them if you're being treated for cancer.

Who it’s for

People who work out regularly and want to build muscle (avoid if in cancer treatment or with liver or kidney disease)

Daily dose

Within the label dose. Avoid taking high doses for a long time

When

Before or after exercise; as amino acids, they're best on an empty stomach

Best form

Powder or capsule supplements. Amino acids from food are nothing to worry about

What are BCAAs?

BCAAs (branched-chain amino acids) is the name for three amino acids (small building blocks of protein): leucine, isoleucine, and valine. Your body can't make them, so you have to get them from food.

They help flip the switch that builds new muscle. That's why people who work out often take them to support muscle building.

Protein foods like meat, fish, eggs, and beans already contain plenty. Getting them from food is no problem at all. The thing to watch is taking high doses as supplements.

Best time to take BCAAs

  • If your goal is better workout results, take them before or after exercise.
  • As amino acids, they absorb better on an empty stomach.
  • Don't go over the amount listed on the product.

Who should not take them

  • People in cancer treatment: BCAAs switch on the body's growth switch (mTOR, a signal that makes cells grow and multiply). That's good for muscle, but cancer cells may use the same signal to grow. Avoid high-dose supplements.
  • People with liver problems: They're concentrated amino acids, so your liver has more to process. There are reports of raised liver enzymes.
  • People with kidney problems: Your kidneys have to filter the waste produced when protein breaks down, which adds strain.

BCAA side effects: liver and kidneys

SituationRisk
Amino acids from foodNo problem
Supplements at the label doseGenerally fine
Too much from supplements + intense exerciseMay put more strain on your kidneys
Supplements in large amounts over a long timeCases of raised liver enzymes and liver or kidney damage have been reported
It's easy to stack several workout supplements, like BCAAs, protein powder, and creatine. Take a moment to add up your total protein and amino acid intake.

If your urine gets very foamy, your body swells, or you feel unusually tired, stop the supplements you've been taking and get your liver and kidney levels checked by a doctor.

Medications and conditions to watch

  • Caution Cancer treatment — May switch on growth signals (mTOR) — avoid high-dose supplements
  • Check Liver or kidney disease — Adds to the work of processing amino acids — talk to your doctor before taking

Frequently asked questions

How much BCAA should I take a day?

Don’t go over the amount on the label. Most products are about 5 g per serving (one scoop), and 1–2 servings on training days is plenty. If you already get enough protein from meat, eggs or a protein shake, you likely don’t need extra BCAAs.

When should I take BCAAs?

If your goal is better workout results, take them before or after exercise. As amino acids, they're best on an empty stomach.

Are BCAAs bad for your liver?

Taking them at the label dose is generally fine, but there are cases of raised liver enzymes after taking high-dose supplements for a long time. Avoid them if you have liver problems.

Are BCAAs hard on the kidneys?

Taking a lot while doing intense exercise may put more strain on your kidneys. Check your total intake so it doesn't overlap with other protein supplements.

Can people with cancer take BCAAs?

It's best to avoid high-dose supplements because they may switch on cell-growth signals. Protein from food is nothing to worry about.

Related concerns

Liver health

Last updated 2026-10-19