The expression “anabolic nutrient” is much bandied about these days
in articles and ads. It suggests that a particular nutrient may promote
growth processes, particularly in muscle tissue. Despite the
hype and
hyperbole attached to the term, however, the only real anabolic
nutrients are protein and amino acids.
Protein is made up of 22 amino acids, some of which are considered
essential, while others are nonessential. The difference is that the
essential amino acids, of which there are nine, must be supplied in the
diet, while the unessential aminos can be synthesized from the essential
amino acids and other nutrients.
Research in recent years has shown that when it comes to muscle
protein synthesis, which is the main process that results in muscle
growth, essential amino acids are the key. And you don’t need a lot.
As
little as six to eight grams of essential aminos is all that’s required
for promoting maximum muscle protein synthesis after training. You can get that in about 25 grams of whey protein.
Of the essential amino acids, the most anabolic are the
branched-chain aminos. They are often referred to as “the muscle aminos”
because, unlike other aminos, which are metabolized in the liver, the
BCAAs are metabolized primarily in muscle. In fact, muscle itself
consists of 60 percent BCAAs.
There are three BCAAs—leucine, isoleucine and valine—with leucine
being the most potent in aiding the growth process. That relates to its
ability to stimulate directly a protein complex called mammalian target
of rapamycin—mTOR for short. When mTOR is stimulated, it initiates a
cascade of other signaling factors that results in upgraded protein
synthesis. No other amino acid comes close to the potency of leucine in
triggering mTOR activity.
One recent study examined four varied protein sources—wheat, soy,
eggs and whey—in terms of their ability to stimulate protein synthesis
in rats.
1 Their leucine contents vary as follows: wheat, 6.8
percent; soy, 8 percent; egg, 8.8 percent; and whey, 10.09 percent. The
rats were deprived of food for 12 hours to slow down their muscle
protein synthesis activity and then got meals that contained one of the
above sources of protein.
The whey and egg meals produced the highest rates of muscle protein
synthesis, which correlates to their higher leucine contents; however,
an important point was what the study showed about dosage. Once a
critical amount of leucine was ingested, consuming any more didn’t
further extend the protein-synthesis effect.
Looking at it another way, there is a minimal threshold of leucine in a meal that promotes muscle protein synthesis. So
the take-home point of this study is that when you’re eating smaller
protein meals, the leucine content is the critical factor for
stimulating growth. A corollary is that you can get all the benefits
of protein, even with small meals, by choosing higher-quality proteins
that are richer in leucine, such as eggs, milk and whey.
Leucine’s potent effect was illustrated in the study when the
researchers supplemented the wheat protein with additional leucine. That
produced a protein-stimulating effect similar to that of whey. My
interpretation is that if you’re eating lower-quality protein foods,
such as wheat or vegetables, you can considerably boost the
protein-synthesis effect simply by also taking in a higher-quality
protein, such as whey, at the same time.
Another study examined just how potent leucine is in promoting muscle protein synthesis.
2
Twenty-four men took part in the experiment, in which the researchers
tested a dose of whey that was considerably less than the 25 grams that
has been found to maximize protein synthesis. Instead, the subjects got
6.25 grams, which contains 0.75 grams of leucine, as compared to the
three grams contained in 25 grams of whey. The men first did a set of
one-legged extensions before having one of the following meals:
1) 25 grams of whey protein
2) 6.25 grams of whey with added leucine, enough to equal the content of 25 grams of whey
3) 6.25 grams of whey with essential amino acid content equal to that of whey for all aminos except leucine
The results showed that adding the leucine to a smaller dose of whey
did provide a postmeal boost in muscle protein synthesis, but it was
short-lived, lasting only one to three hours. Even the whey with the
added aminos minus leucine led to only a temporary boost. Only the
greater dose of whey produced a sustained boost in protein synthesis
that lasted three to five hours. That was true even though the blood
amino acid elevations provided by all the sources usually return to
baseline about 2 1/2 hours after the peak plasma amino spike.
The authors suggest that the nonessential amino acids may be the
key to the sustained rate of protein synthesis produced by whey. This
study also underscores the fact that while leucine may be a key arbiter
of muscle protein synthesis, you still need the presence of other amino
acids for it to proceed at an optimal rate. Specifically, if you
provide a large amount of other amino acids, you don’t need a large dose
of leucine to trigger protein production.
Although leucine is most known for its positive effect on protein
synthesis, it has a few other attributes that can be very helpful for
bodybuilding purposes. Relating to body composition,
in the hypothalamus section of the brain, leucine helps to reduce appetite by modifying the activity of leptin, a protein produced by fat cells. Leptin signals the brain, which turns off sensations of hunger.
Once leucine has done its work in relation to muscle protein
synthesis, excess leucine can be converted into other amino acids, such
as alanine and glutamine. That helps to maintain blood glucose under
carbohydrate-restricted conditions. In other words, it helps you
maintain energy when on a low-carb diet.
In addition,
leucine appears to aid in the creation of
mitochondria, the cellular structures where energy is produced as ATP
and fat is burned. Leucine also blunts the release of certain
peptides in the brain that are associated with intense food cravings,
and as such it helps in the fat-loss process.
Mice that are fed a high-fat diet but supplemented with leucine show a
32 percent reduction in weight gain along with 25 percent less bodyfat.
The fat loss is related to an uptick in the activity of thermogenic
proteins that turn fat calories into heat. The effect may be more potent
in mice, as they have more of the highly thermogenic brown adipose
tissue than humans. In one study of mice on a high-fat diet, the
subjects showed all the symptoms of the metabolic syndrome, including
obesity, fatty liver, insulin resistance and negative inflammatory
changes in fat cells.
Yet, giving them leucine blocked most of those negative metabolic syndrome effects.
Another recent study found that a combination of leucine and vitamin B6 may significantly boost bodyfat loss.
3The
supplement consisted of 2.25 grams of leucine and 30 milligrams of B6.
Cell culture studies had previously shown that leucine exerts a
partitioning effect, diverting energy from being stored in fat to being
burned in muscle. Leucine increases the activity of genes that control
fat release and encourages muscle-fat oxidation. The B6 is added because
its actions appear to blunt an enzyme called fatty acid synthase that
is an important player in the fat-storage process.
The combination of
leucine and B6 boosted fat burning in human subjects by 33.6 grams a
day while also reducing oxidative and inflammatory markers. In
addition, the supplement boosted by 67 percent levels of adiponectin, a
fat-cell protein associated with reduced inflammation and increased
insulin sensitivity.
The same authors also published a study that examined the effects of
combining either leucine or its metabolite, HMB, with resveratrol.
Resveratrol is currently a superstar nutrient because numerous animal
studies have shown that it blunts many of the processes in the body
associated with aging.
Animal-based studies also show that resveratrol can dramatically
boost exercise tolerance and may aid in helping to control insulin
resistance while encouraging bodyfat loss. That said, the doses that
accomplished those effects in animals were massive compared to the
levels of resveratrol found naturally. You would need to drink thousands
of bottles of red wine (a good natural source of resveratrol) to obtain
similar doses. Still,
the new study showed that when low doses of
resveratrol are combined with either leucine or HMB, the effect is
synergistic, leading to body-composition changes similar to those seen
with huge doses of resveratrol. Of course, this study involved
rodents, so we don’t know yet whether the effect also occurs in humans.
We do, however, know that the mechanisms behind the effect exist in
humans.
So how much leucine should you get to promote muscle protein
synthesis and fat loss? The usual suggested dose is 2.5 grams per meal
and another 2.5 grams taken 1 1/2 hours after the meal to help extend
muscle protein synthesis.
—Jerry Brainum
Editor’s note: Have you been ripped off by supplement makers
whose products don’t work as advertised? Want to know the truth about
them? Check out
Natural Anabolics, available at
JerryBrainum.com
1Norton, L., et al. (2012). Leucine content of dietary
proteins is a determinant of postprandial skeletal muscle protein
synthesis in adult rats.
Nut and Metabol. 9:67.
2Churchward-Venne, T.A., et al. (2012). Supplementation of
a suboptimal protein dose with leucine or essential amino acids:
effects on myofibrillar protein synthesis at rest and following
resistance exercise in men.
J Physiol. 590:2751-2765.
3Zemel, M.B., et al. (2012). Effect of a leucine and
pyridoxine-containing nutraceutical on fat oxidation and oxidative and
inflammatory stress in overweight and obese subjects.
Nutrients. 4:529-41.
©,2015 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited
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