Do bcaas increase muscle size

If you want more muscle than you have right now, BCAA supplements are quite possibly the most valuable supplement in the entire known universe.

Take them before and after a workout, as well as between meals, and your muscles will grow larger at a rate faster than you ever thought possible.

That’s the theory, anyway. But I’m not convinced.

At first glance, the research on BCAA supplements looks extremely exciting.

You’ll see lots of complicated and scientific explanations about the mTOR signaling pathway, mRNA translation, p70S6K phosphorylation and a bunch of other acronyms that you’ve never heard of.

But dig a little deeper, and you’ll find that BCAA supplements are nowhere near as important as some would have you believe.

Do BCAAs Work for Muscle Growth?

Probably the most relevant benefit to anyone who wants more muscle is the fact that BCAAs increase the activity of signaling pathways involved in muscle growth, boosting protein synthesis in muscle tissue [5].

Of the three, leucine (pronounced loo-seen) appears to be the most important, serving as both a “trigger” for protein synthesis, as well as a substrate for newly synthesized protein [8].

But the benefits don’t end there. Taken before and after resistance exercise, BCAAs can also reduce both markers of muscle damage as well as delayed-onset muscle soreness (DOMS).

In one 12-day study, participants took either 10 grams of a BCAA supplement or a placebo twice a day (morning and evening) [3]. In addition, after an overnight fast, they took a further 20 grams of BCAAs one hour before exercise and again immediately afterwards.

Muscle soreness peaked two days after the workout. But the level of soreness was significantly lower when subjects took BCAAs. There was also less muscle damage and a faster recovery of muscle function in the BCAA group.

There’s also evidence that BCAA supplements can improve the “anabolic hormonal profile” during a period of high-intensity strength training [7].

A group of “recreationally active” men was assigned to either a BCAA or placebo group. They took the supplement, which contained 3.3 grams of BCAAs and 2 grams of glutamine, for three weeks. In the fourth week, they carried on taking the supplement but also lifted weights on four separate occasions.

Alongside a reduction in markers of muscle damage, the researchers also found that the testosterone: cortisol ratio – used for studying and preventing overtraining syndrome in various sports – was significantly higher when the men took BCAAs.

If I was trying to sell you on the benefits of BCAAs, I’d stop right there.

But that would be a little like reviewing a movie based on the trailer alone – you’re only seeing the good stuff, and the impression you come away with is based on an extremely limited amount of information.

BCAAs in Food

First, a supplement is not the only source of BCAAs. In fact, you might be surprised to learn how many BCAAs you get from the food you eat.

As an example, around 15% of the protein in chicken or beef comes from BCAAs. For every 25 grams of protein from chicken, which is roughly what you’ll find in a skinless chicken breast, you’re getting around 4 grams of BCAAs. The level of BCAAs in whey protein is even higher – 25 grams of protein from whey provides around 6 grams of BCAAs.

If your protein intake is relatively high, and that protein comes from a range of high-quality sources (i.e. chicken, beef or milk), chances are you’re already getting plenty of BCAAs from your diet.

Second, very few of the studies out there have looked at what happens when you give BCAA supplements to people who are already eating enough protein.

For instance, the study that looked at the effect of BCAAs on the testosterone: cortisol ratio actually excluded subjects who were eating more than 0.4 grams of protein per pound of bodyweight per day. We can’t assume that the results will apply to people who are already consuming “adequate” amounts of protein.

What About Leucine?

Given that leucine has proven more effective than the other BCAAs at promoting protein synthesis, there have been a number of studies to look at the effect it has by itself.

At first, leucine showed a lot of promise, especially in studies that looked at short-term changes in muscle protein balance. But it hasn’t delivered the goods when it comes to producing measurable gains in muscle mass over longer periods of time.

Here’s how one group of scientists summed up the research so far:

“Studies in both elderly humans and rodents subjected to free leucine supplementation have shown that such supplementations indeed acutely improved muscle protein balance after food intake by increasing muscle protein synthesis and decreasing muscle proteolysis in the postprandial state. However, the few chronic studies conducted with such free leucine supplementations did not succeed in promoting an increase in muscle mass.”

Unfortunately, most of the data they looked at comes from research on elderly subjects and rodents. What happens when leucine is given to a group of young, healthy men lifting weights for 12 weeks?

That’s exactly what happened in a Leeds Metropolitan University study, where a group of 26 untrained men received either four grams of leucine per day or a placebo on top of their regular diets [4].

After 12 weeks of lifting weights, the leucine group got better results across the board. Strength gains were around 30% higher compared to the placebo group. They also gained 60% more muscle mass, despite the fact that both groups followed the exact same training program and much the same diet.

All of which sounds pretty compelling.

If I wanted you to buy some leucine, this is exactly where I’d insert the “buy now” button.

But once again, the devil is in the detail. The average weight of the men taking part in the trial was 172 pounds. Yet they were getting just 94 grams of protein per day, or the equivalent of 0.5 grams of protein per pound of body weight.

A couple of scoops of whey protein would have bumped up their protein intake by around 50 grams per day, as well as providing around 50% more leucine than they were getting from the supplement [2]. While leucine may have proven effective, it did so only against a background of an insufficient protein intake.

In fact, follow-up studies show that as long as you’re getting enough protein in your diet, taking extra leucine has no effect on muscle growth [10, 11].

Is It Worth Taking BCAAs Between Meals?

Taking BCAAs between meals is supposed to accelerate gains in muscle mass by overcoming something called the refractory response, which describes the phenomenon whereby muscle protein synthesis drops despite amino acid levels in the blood remaining high.

The idea is that you space your meals 4-6 hours apart to allow amino acid levels in the blood to drop, rather than maintaining them at continuously high levels by eating more frequently. Leaving longer between meals is supposed to help “re-sensitize” muscle to the anabolic effect of amino acids.

Then, somewhere in the middle of this 4-6 hour window, you take a BCAA mix containing 2-3 grams of leucine. Because BCAAs are rapidly digested they create a “spike” in blood amino acid levels. This is supposed to trigger an extra round of protein synthesis without interfering with the “anabolic response” to the subsequent meal.

It’s an interesting theory.

But it remains a theory, based largely on research that looks at changes in muscle protein synthesis over a number of hours, rather than actual gains in muscle mass over a period of several months [1, 6]. There’s often a disconnect between the two, and the former is not always a completely dependable way to predict the latter [9].

There’s currently no published data to show that this approach has any impact on muscle growth in humans. I don’t think it’s going to do you any harm. But the size of the effect, assuming that one even exists, is likely to be an extremely small one.

Summary: Do BCAAs Work?

In summary, there’s plenty of research out there to show that BCAAs have a number of benefits as far as muscle growth is concerned.

But there’s little evidence to suggest that it matters where those BCAAs come from – a chicken breast, a scoop of whey protein or a BCAA supplement. Once they’ve made it to the bloodstream, they’re going to do exactly the same thing.

Moreover, most studies have measured short-term changes in protein synthesis, rather than long-term gains in muscle mass. Very few have looked at the effects of BCAA supplements on top of an adequate protein intake, or compared free-form BCAAs with an equivalent dose of BCAAs from a milk protein supplement or even just food.

Although BCAAs by themselves can increase muscle protein synthesis, the increase is relatively short-lived.

In one study, both six grams of BCAAs and 30 grams of milk protein (providing an equivalent amount of BCAAs) led to an increase in muscle protein synthesis [12]. But it was only milk protein that maintained elevated levels of muscle protein synthesis for a full five hours. With BCAAs, it was back to normal after two hours.

It’s true that taking BCAAs before and after training can reduce markers of muscle damage and soreness, as well as accelerating the recovery of muscle function.

But if you compare large doses of BCAAs with large doses of nothing, particularly in someone on a low protein intake, this shouldn’t come as any great surprise.

If you want to get some BCAAs in your system before and after a workout, a scoop of whey protein will do the job just fine.

Despite the hype, there’s little solid evidence to show that BCAA supplements offer any significant advantage over and above an adequate intake of high-quality protein from food and/or milk protein supplements.


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Christian Finn is the nation’s leading authority on science-based, joint-friendly ways to build muscle. A former "trainer to the trainers," he holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.

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