Milk Nutrients Augment Muscle Growth and Recovery

Written by: Lauren Milligan Newmark, Ph.D. | Issue # 40 | 2015

As anyone who has watched a professional bodybuilding contest can attest, muscle tissue is quite adaptable. In fact, muscle has been called the most adaptable tissue in the human body because it is constantly responding to mechanical strain. When a muscle is placed under strain (like a bicep curl or bench press), the muscle fibers are damaged and respond by fusing together and increasing in mass. Because muscle fibers are made of protein, this repair and growth process can be augmented by nutrition. Decades of research have investigated just which nutrients may best support muscle development, with the bulk of the research focused on milk-derived whey proteins. From everyday gym rats to professional athletes, whey protein is associated with gains in muscle mass and decreases in muscle soreness. And milk may yield even more benefits than whey protein supplements alone, offering up whey plus slow-digesting casein proteins, carbohydrates, and electrolytes. Don’t tell the health food stores, but the best fuel for muscles could be in the grocery store’s dairy aisle.

No pain, no gain

As strange as it sounds, a good number of us purposely inflict damage to our muscle tissue on a daily basis in an activity called strength training. A set of bicep curls or leg presses places the associated muscle fibers under strain, which damages the fibers. To repair themselves, the muscle fibers fuse together and increase in diameter and length, thereby creating a larger muscle (1). This gain does not come without pain. Damaged muscle fibers are a site of inflammation that normally lasts between one and three days. With this inflammation comes soreness, tenderness, decreased mobility of the muscle group, and subsequently decreases in agility and muscle performance. Researchers refer to this as delayed onset muscle soreness (DOMS) and it is considered a normal side effect of the muscle rebuilding process (1-3).

The science of recovery nutrition is based on the cellular processes associated with muscle development. While we may normally picture a cell as a sphere, muscle cells (commonly referred to in the literature simply as muscle fibers) are actually shaped like tubes. Each tubular muscle fiber is itself composed of hundreds of tube-like structures called myofibrils, and within these myofibrils are thin strands of proteins. Picture an empty paper towel roll (the muscle fiber), filled with drinking straws (the myofibrils), which are in turn filled with uncooked spaghetti noodles (the proteins). Muscle growth is an increase in the diameter of the muscle fiber, which is accomplished by an increase in myofibril size due to increased protein synthesis (the addition of more spaghetti noodles means wider straws, which means a wider paper towel roll). Muscle growth is thus highly dependent on protein synthesis within muscle tissue (1).

Getting more bang out of your workout buck

It is not surprising, then, that a great deal of research has gone into investigating particular nutrients that can activate, enhance, and support muscle protein synthesis in conjunction with resistance exercise (4). In a meta-analysis of 22 studies including nearly 700 different subjects, Cermak et al. (4) found that protein ingestion after even a single instance of resistance exercise functioned to inhibit muscle breakdown and increase muscle protein synthesis (or, an overall anabolic effect). Although there were some discrepancies across the studies in outcome measurements, results from studies that involved training programs longer than six weeks overwhelmingly support the hypothesis that protein supplementation during resistance training increases muscle mass (by increasing fiber diameter) and muscle strength.

But will just any protein do? In Cermak et al.’s meta-analysis (4), the majority of the studies reviewed (18 out of the 22) included a whey protein supplement. Whey proteins are only found in milk and are included in nutritional intervention experiments because of their unique amino acid composition. Whey proteins are especially rich in branched chain amino acids (BCAA), including leucine. Protein synthesis begins in the nucleus when the DNA receives a chemical signal that it needs to manufacture proteins. Leucine and other BCAA found in whey are believed to act as this molecular signal to the many nuclei of muscle fibers (5, 6).

In one of the longest nutritional intervention experiments to date, Volk et al. (6) demonstrate the role of leucine and whey protein in activating muscle protein synthesis (an anabolic action) as well as preventing muscle protein breakdown (an anti-catabolic action). One hundred and forty-seven men and women between the ages of 18 and 35 were placed into one of three supplement categories: whey, soy, or carbohydrate. Regardless of the supplement type, each study subject completed 96 resistance-training workouts over approximately nine months with a professional trainer. The researchers went to great lengths to ensure as much homogeneity across the groups as possible, particularly in total protein consumption before supplementation. Protein intake was approximately 1.4 grams (g) per kilogram (kg) of body weight in the soy and whey groups compared to 1.2 g/kg in the carbohydrate group.

At the end of the study period, all three groups had increased their lean body mass, but the largest increase was found in the whey group. Interestingly, there was no significant difference in the amount of lean body mass gained between the soy protein and carbohydrate groups, despite the soy group consuming approximately 22 g more protein per day. Volk et al. (3) use this finding to argue that it is not the total grams of protein that matter for muscle growth, but the types of amino acids in those proteins. The greater gain in lean mass in the whey supplement group was attributed specifically to higher concentrations of BCAA in whey compared to soy protein (approximately 50% more) (6). Subjects in the whey group had more than two-fold higher post-workout plasma leucine concentrations than the soy group. Moreover, fasting leucine levels were also highest in the whey group, indicative of a higher overall leucine availability. Volk et al. (6) suggest that the anabolic surges that occur after a workout, and the overall greater exposure of muscles to leucine among the whey supplement subjects, led to increased net muscle protein balance (more protein synthesis, less protein breakdown).

Milk: whey, and way more

Cow’s milk is a whole food source of whey protein, so it stands to reason it may have similar benefits to muscle development as whey supplements. But are there any additional benefits for consuming it straight from the source as opposed to the powdered form? Several studies have investigated milk’s role in muscle development, focusing specifically on the recovery process. Recall that muscle growth is initiated by muscle damage. As muscles repair themselves and grow, there is a period of decreased muscle function, which can manifest itself as reduced agility and reduced strength in the damaged muscle groups. For the everyday gym goer, this may be a small inconvenience. But for trainers and coaches of professional athletes, decreasing the recovery period and limiting the effects of exercise induced muscle damage (EIMD) is of critical importance.

Milk contains both proteins and carbohydrates, the combination of which is believed to play a role in increasing the repair of muscle protein structures and decreasing protein degradation within muscle tissue (2, 7, 8). Further, consuming proteins alongside carbohydrates can improve subsequent endurance or strength exercise performance. While whey alone may improve gains in lean body mass, milk’s combination of rapidly digested whey proteins, slowly digested casein proteins, and carbohydrates (lactose) work together to improve muscle recovery and future performance.

Cockburn et al. (2) found that the consumption of 500 ml of low-fat milk (approximately 2 glasses) immediately after muscle-damaging exercise limited reductions in muscle function measured 48 and 72 hours later compared to a placebo drink. The same research group also identified a positive effect of milk consumption on muscle recovery in athletes involved in field-based sports, such as soccer and rugby (7). Participants completed a 90-minute shuttle run activity one week before and 48 hours after engaging in a muscle damaging exercise that targeted the hamstrings. The shuttle run was designed to simulate the bursts of speed and physical endurance seen in field-based sports. As in the previous study, 500 ml of milk or a placebo was consumed immediately after completing the muscle damaging exercise. Comparing shuttle run performance before and after muscle damage was used as a proxy for how well each athlete would be able to perform in an actual match two days after training. In addition, they also measured agility and overall muscle force in the hamstrings. While the groups did not differ in several of the outcome measurements (e.g., countermovement jump height and muscle soreness), the study did find that milk consumption limited the reductions in muscle performance that are required for field-based sports, such as sprint times during the shuttle run.

The timing of milk consumption directly after EIMD is an important feature in these (2,7) and many other studies (5, 8, 9) that look at milk as a recovery beverage. After resistance or endurance training, muscles have decreased energy (glycogen) stores and need immediate refueling in the form of carbohydrates. Delays in providing damaged muscles with carbohydrates are associated with increased recovery periods (9). Milk also has demonstrated benefits in post-exercise hydration, outperforming other well-known carbohydrate beverages including Gatorade.

Milk as recovery nutrition

Professional and recreational athletes alike are interested in finding the ultimate recovery beverage. While there are dedicated aisles in health food stores to muscle building powders and others to carbohydrate recovery drinks, milk may be the only beverage that can boast the ability to play a role in both. And believe it or not, chocolate milk may be an even better recovery drink, particularly for endurance sport athletes such as runners and cyclists, because it offers all the same essential amino acids but has more carbohydrates than regular milk (10). It might not come in fancy packaging or have a catchy name, but milk might be the next big thing in recovery nutrition.

References

Back to SPLASH!^® Home