Milk protein has emerged over the past few years as the preeminent protein source for building muscle. While other protein foods, such as eggs, fish and meat, also provide top-grade protein, milk stands out because of its high biological value, its ease of digestion and its content of various bioactive peptides that go beyond just boosting muscle protein synthesis and have definite health benefits as well.
Most bodybuilders and athletes prefer to get their milk protein in supplement form, rather than drinking whole milk or eating a lot of dairy products, as they believe that dairy foods contain too much carb and fat. Others believe that milk contains estrogen, a steroid hormone associated with increased fat deposition, especially under the skin. Bodybuilders prefer to stick with concentrated protein supplements, which are devoid of excess calories, fat and carbs.
The point to keep in mind about protein supplements is that they’re nothing more than concentrated food protein. They offer a convenient way to take in greater amounts of protein without also getting additional calories, which gives you greater control of your body composition while you’re building muscle.
Commercial milk protein supplements contain two types of milk protein, whey and casein. While some have both types, others focus only on whey. Casein-based products are also available, although whey is far more popular because of its higher amino acid content and ease of digestion and absorption. To further complicate the situation, whey protein supplements come in varying forms—whey concentrates, whey isolates and hydrolyzed whey. They vary in protein content as well as carbs (in the form of lactose) and fat. The whey concentrates often feature less protein, averaging about 80 percent, and also about 5 percent lactose. Even so, the concentrates retain all of the beneficial whey bioactive peptides.
Whey isolates have a higher protein content, about 90 percent or more, and also retain most of the active peptides—but they are much more expensive than the concentrates due to the additional processing involved.
Hydrolyzed whey features a predigested array of amino acids, making it the most rapidly absorbed form. Since the quick availability of amino acids postworkout plays a dominant role in kick-starting muscle protein synthesis, hydrolyzed whey is considered the best form to get after a workout. In truth, however, whey is so rapidly absorbed that the uptake advantages offered by hydrolyzed whey are not as significant as you might expect. That’s especially true when you consider that muscle protein synthesis peaks 48 hours after a weight workout.
The primary differences often cited between whey and casein are related to their absorption properties. Whey, as noted, is a rapidly absorbed protein that peaks about an hour after ingestion and is gone by the 90-minute mark. In contrast, casein is a slowly absorbed protein that actually curdles in the stomach, which provides a slow release of amino acids that lasts as long as seven hours.
Thanks to its rapid amino acid uptake, whey is generally considered to be superior to casein for boosting muscle-protein-synthesis; however, the slow-release property of casein suggests that it is ideal for triggering an anticatabolic effect in muscle. Specifically, having a higher concentration of amino acids in the blood tends to boost insulin, which helps lessen muscle protein breakdown. The greater amino acid content also tends to offset the effects of cortisol, an adrenal steroid hormone that is the major catabolic hormone in the body.
Since the effects of casein last for seven hours, it seems reasonable to assume that taking a casein-based supplement before going to sleep will have not only a major anticatabolic effect but also a way to boost muscle protein synthesis during sleep.
A major feature of the sleep process is body restoration, which includes repair of damaged tissues. It’s one reason that growth hormone peaks during the first 90 minutes of sleep, with the onset of deep sleep cycles. It stands to reason, then, that the slow-drip amino acid release provided by casein would enrich the normal sleep-restoration process and also significantly add to muscle protein synthesis, translating into increased muscle growth.
Although casein is often recommended for this late-night anabolic boost, it’s effectiveness has never actually been tested until recently. A group of scientists from the Netherlands decided to measure the effects of taking casein before bedtime on muscle protein synthesis.1 Sixteen young, healthy, active men who were not athletes were divide into two groups, with one group getting 40 grams of casein and the other a placebo before going to sleep. To measure the effects on muscle protein synthesis, the researchers added a tracer of the amino acid phenylalanine and gave the men an amino acid intravenously as they slept.
During the day the men ate a conventional diet containing 57 percent carb, 13 percent protein and 30 percent fat, which came to an average of 1.2 grams of protein per kilogram—2.2 pounds—of bodyweight. They weight trained in the evening, doing only lower-body exercises and taking 45 minutes to complete the workout. Following the workout, they had drinks that contained 60 grams of carb and 20 grams of whey protein. Before sleep they got either the tracer-enriched casein or a placebo. During the night the researchers monitored the rate of amino acid uptake from the casein and found a substantial rise in plasma amino acid content that lasted throughout the night, as expected. Half of the ingested casein became available as plasma amino acids. Why only half? The authors didn’t discuss that in detail, but I suspect that the other half was oxidized. It takes surprisingly small amounts of essential amino acids—say, six to 10 grams—to maximize muscle protein synthesis after training, and any aminos not used for that purpose are oxidized in the liver.
The scientists observed a higher rate of whole-body protein synthesis throughout the night after the subjects drank the casein supplement. Whole-body protein synthesis doesn’t reflect the rate of muscle protein synthesis, however, so the scientists also collected muscle biopsies before and after the casein ingestion to determine the actual muscle-protein-fractional-synthetic rate. They found that direct muscle protein synthesis was 22 percent higher in those who got the casein before sleep than in the placebo group. The researchers speculate that the rate of muscle protein synthesis produced by the casein was greatest during the first four hours of sleep, but they took measurements only during that time, so they don’t know for sure how long the muscle proteins synthesis was sustained, although they suspect that it was longer than four hours, considering casein’s seven-hour absorption rate.
Besides its obvious implications for bodybuilding, the authors suggest that this confirmation of the anabolic properties of casein could also greatly benefit older people, most of whom suffer from a relative anabolic blocking effect because of their inability to use amino acids from meals completely. I would further suggest that it could also benefit bodybuilders over 40, who don’t absorb amino acids as easily as their younger peers. Since recovery is one of the major differences between the young and the old, casein’s overnight anabolic boost may provide a definite anabolic advantage for those over 40 who are engaged in regular weight training.
So, based on this and other studies, it seems prudent to use a whey protein supplement before and after training to take advantage of the rapid digestion and uptake and switch to a casein-based supplement to maximize nighttime anabolic activity and blunt the early-morning rise of cortisol. Or you can get the best of both worlds by using a supplement that features both, which gives you the rapid amino acid uptake of whey as well as the longer, slow release of casein. The preferred form of casein is micellar casein, which undergoes minimal processing, leaving the beneficial peptides intact.
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1 Res, P.T., et al. (2012). Protein ingestion prior to sleep improves post-exercise overnight recovery. Med Sci Sports Exerc. 44(8):1560-9.