Much has been made in recent years of the importance of nutrient timing, a.k.a. making sure that you get adequate amounts of protein and carbohydrates after you train. Research shows that there’s a two-hour metabolic window of opportunity after a workout, in which the effects of the exercise interact with elevated enzymes to produce a heightened absorption of nutrients.
Getting just protein then is enough to trigger muscle protein synthesis, and the active portions of protein for that are essential amino acids. It takes as little as six to 10 grams of essential amino acids to produce a maximum rate of protein synthesis. That translates to 20 grams of protein in your postworkout feeding.
As I’ve discussed in previous installments of this column, researchers found the 20-gram dose to be ideal after providing various amounts of protein (up to 40 grams) to subjects postworkout and then measuring the extent of muscle protein synthesis. The one exception is for those over age 40, who have a certain amount of anabolic resistance and so need more protein.
Most studies that have tracked muscle protein synthesis after resistance training have gone no longer than six hours, but it’s known to be accelerated for 24 hours if trainees get the optimal amounts of nutrients. So can we forget about the two-hour “anabolic window” after a workout? The answer is no—for reasons that I’ll get into below. The more important question at this point is, If muscle protein synthesis is elevated for 24 hours after training, what’s the ideal protein-meal schedule to take advantage of that?
A new study reveals precisely how much protein to get and how often to get it in during the 12 hours after a workout.1 Twenty-four healthy young men, all of whom had at least two years of training experience, were assigned to three groups, with all subjects getting 80 grams of whey protein over a 12-hour period after a workout consisting of four sets of leg extensions. Here’s the breakdown of the groups and what they took in:
1) The pulse group got eight servings of 10 grams of whey protein, one every 1.5 hours after the workout.
2) The intermediate group got four servings of 20 grams, one every three hours.
3) The bolus group got two servings of 40 grams, one every six hours.
Muscle biopsies were taken from the subjects at rest and at one, four, six, seven and 12 hours after exercise. The total protein intake of 80 grams amounted to 1.5 grams per kilogram of bodyweight, and they also got four grams of carbohydrate per kilogram of bodyweight. The protein was tagged with an amino acid tracer to determine the extent of protein synthesis.
The results showed that taking in 20 grams of whey protein every three hours following a workout leads to the greatest rate of production. Feeding yourself more often than that would not improve the outcome because of what’s known as a “muscle full” effect. Basically, muscle becomes immune to amino acids if they are provided continuously for more than two hours. Protein synthesis stops despite all the amino acids still in the blood. Intakes of more than 20 grams are rapidly oxidized in the liver, so you waste anything beyond that. Getting 20 grams every three hours is just enough to stimulate protein production but not enough to cause the muscle-full effect.
The two bolus feedings, 40 grams of whey every six hours, produced the greatest amount of amino acid transport activity, in addition to blunting muscle breakdown, but that lasts only through the first four hours after the workout. By the six-hour mark it was no longer apparent, and the aminos from the extra 20 grams of protein were oxidized in the liver.
One notable caveat about this study is that the subjects were not very big and were also lean. Whether the results would apply to larger and/or obese men is not known. Also, it used a fast-acting protein source, whey, rather than actual food meals. Consequently, the results are more pertinent to having a whey-protein supplement than eating a meal that contains carbohydrate and fat as well as protein, which would slow its digestion significantly in comparison to whey only. What’s more, amino acids are known to stay elevated in the blood for an average of five hours after a high-protein meal, which suggests that meal timing of food meals to optimize muscle protein synthesis would be different from that of whey protein alone.
Free Radicals and Muscle Gains
Free radicals, also known as reactive oxygen species, or ROS, are by-products of oxygen metabolism that are known to be involved in various diseases as well as exercise metabolism. Past studies have linked elevated free radicals produced during exercise with increased muscle soreness and a blunting of recovery. To combat that, various antioxidant nutrients, such as vitamins C and E, are often suggested as a means of promoting better recovery from exercise.
On the other hand, the body is known to upgrade its in-house antioxidant system with continued training, and the various enzymes and proteins act as a built-in fail-safe mechanism against the increased ROS.
Some studies suggest that the body’s defense system is easily overwhelmed by intense and extensive exercise. By adding various dietary antioxidants, you can bolster your antioxidant reserve.
All that said, more recent studies, especially those done with endurance exercise, show that free radicals may offer some important advantages. For one thing, a higher rate of free-radical production promotes the development of mitochondria, the portion of the cell where fat is oxidized, and energy, in the form of ATP, is produced.
According to some studies, taking antioxidants close to a workout interferes with the ROS-induced beneficial changes and may blunt the beneficial effects of exercise on insulin sensitivity. Not all studies have found those negative points, so the issue of whether antioxidant supplements interfere with the exercise-induced ROS benefits is still open for discussion.
The picture is even less clear regarding the effects of ROS on muscle growth. One particular ROS, known as peroxynitrate, results when the free radical superoxide comes into contact with nitric oxide. Peroxynitrate is considered a particularly potent ROS, yet recent studies show that it’s involved in the calcium signaling process within muscle that plays an integral role in growth, which suggests that trying to control it may interfere with muscle gains.
One recent rat-base study showed that giving vitamin C to rats that had been exposed to a form of resistance exercise resulted in a blockage of the rats’ muscle gains.2 The catch here is that rats, unlike humans, can synthesize vitamin C in their bodies from glucose. So giving exercising rats a large dose of vitamin C is an unnatural act that may have produced a stress effect sufficient to interfere with the animals’ exercise response.
The studies that have been published thus far about antioxidant supplementation and muscle growth show no interference whatsoever, which should be good news for those who take antioxidants. On the other hand, as noted with peroxynitrate, ROS do seem to play a role in the cellular signaling process that is involved in muscle growth. So the end of this story hasn’t yet been written. —Jerry Brainum
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1Areta, J.L., et al. (2013). Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 9:2319-2331.
2 Makanae, Y., et al. (2013). Vitamin C administration attenuates overload-induced skeletal muscle hypertrophy in rats. Acta Physiol. 208(1):57-65