It has been standard practice for many years for serious athletes to consume a high-carbohydrate meal following intense exercise. As time has gone on, this post-exercise meal has been scrutinized and analyzed to make sure that the correct type of carbohydrates are eaten to maximize the replacement of glycogen lost during exercise.
Following exercise-induced depletion of glycogen stores, levels of the enzyme glycogen synthetase become elevated. This very important metabolic enzyme enables the body to replace lost muscle and liver glycogen. Typical rates of glycogen re-synthesis after short term, high-intensity exercise (i.e. weightlifting) are much higher than glycogen re-synthesis rates following prolonged, lower intensity exercise. This is largely due to the fact that fast twitch muscle fibers, which are the predominantly used during short term, high intensity exercise, have a higher level of glycogen synthetase activity than slow-twitch fibers. (4) What this means is that the body has a greater need (and a greater ability) to restore depleted glycogen stores following short term, high intensity training.
Studies show that delaying the ingestion of a carbohydrate supplement post-exercise results in a reduced rate of muscle glycogen storage. (3) Because of this fact, it’s common to ingest a sugary carbohydrate source following exercise. The Glycemic Index (GI) gives a number to carbohydrates based on how quickly they enter the blood stream. The higher the GI, the quicker it will enter the bloodstream and raise insulin levels. The highest GI food is glucose, with a score of 100. One particular form of glucose (D-glucose, aka Dextrose) quickly became the post-workout carbohydrate of choice based on the speed with which it enters the bloodstream and raises insulin levels. It’s important to understand that not all sugars are created equal. For example, fructose (or fruit sugar) rapidly restores liver glycogen levels at the expense of muscle glycogen stores. The bottom line is that it’s important to ingest quick-acting carbohydrates to begin the repair and rebuilding process.
What if there was a way to improve this practice?
Recently, a new player has emerged in the post-workout carbohydrate war: High molecular weight carbohydrates. High molecular weight carbohydrates (HMW) have shown great promise in providing a wide range of post-workout benefits.
The words most often thrown around when talking about HMW carbohydrates are “gastric emptying” and “osmolality.” These terms essentially go hand in hand with each other. Osmolality, often confused with osmolarity, affects the transport of water and other solutes over the cell membranes. (10) Osmolality is related to the specific osmolality of the blood, which is 280-303 mOsm/kg in humans. A solute that has the same osmolality of blood is said to be isotonic while a solute that has a lower osmolality than blood is hypotonic. The more hypotonic a solution is, the quicker it passes through the stomach into the small intestine where the bulk of nutrient uptake occurs. (11) A very low osmolality means the solution will get to your muscles with great speed and efficiency.
The higher the molecular weight of a carbohydrate, the lower its osmolality. The lower the molecular weight of a carbohydrate, the higher its osmolality. Therefore, a carbohydrate’s molecular weight varies inversely to its osmolality. Knowing this, you can begin to appreciate the difference between HMW carbohydrates and dextrose. The molecular weight of the typical HMW carbohydrate that is marketed today has a molecular weight of 500,000-700,000; whereas, the molecular weight of dextrose is approximately 180. (11) This statistic helps quantify the difference between the two carbohydrate sources. The osmolality of a particular HMW carbohydrate is 11 mOsm/kg in a 5% solution, which is considerably lower than the osmolality of blood at 300 mOsm/kg. With an osmolality that low, the HMW carbohydrate is extremely hypotonic, and we know that the more hypotonic a solution is, the quicker it passes through the stomach into the small intestine.(11) This means that in the world of carbohydrates, the HMW carbohydrate is a Ferrari Enzo, and dextrose is your mother’s Buick Skylark.
In fact, one popular HMW carbohydrate drink has been shown to pass through the stomach 80% faster than dextrose, allowing restoration of glycogen 70% faster than any other carbohydrate. (13) How would you like to like to start rebuilding muscle 70% sooner than you already are after a workout?
One particular study showed that the mean glycogen synthesis rate was significantly higher for a HMW carbohydrate drink compared to a glucose drink for 2 whole hours after ingestion. The scientists in the study concluded that “the osmolality of the carbohydrate drink may influence the rate of re-synthesis of glycogen in muscle after its depletion by exercise.”(6) In essence, the scientists are saying that HMW carbohydrate will get to your muscles significantly faster than whatever carbohydrate you’re currently using.”
Another study that observed glycogen synthesis rates in rats following starvation showed that HMW glycogen was initially synthesized at a faster rate than low molecular weight glycogen. (8) However, blood sugar and insulin levels were not statistically different between the HMW carbohydrate and the glucose solution. What this means is that despite being a complex carbohydrate, the HMW carbohydrate still raised insulin levels to about the same level as dextrose. We’re dealing with a complex carbohydrate that powers through the stomach, causing no bloating, and reaches the blood stream as fast as dextrose; yet, it restores glycogen 70% faster.
Does it sound too good to be true? It gets better.
The osmolality of HMW carbohydrates can potentially speed up the rate of glycogen synthesis post-workout, as well as increase the uptake of whatever vital nutrients are added to the HMW carbohydrate drink. That’s right, all the “stuff” you’ve been ingesting after your workout, in the hopes of getting it to the muscle as quickly as possible, can be sucked up right along with the HMW carbohydrate, faster than ever before. The only problem is that amino-based nutrients such as whey protein, amino acids, and creatine all have a much lower molecular weight than the HMW carbohydrate; therefore, when adding other nutrients into the drink mix, you must consider the effect they will have on the total molecular weight of the solution. In theory, too much protein, creatine, and other nutrients will reduce the effectiveness-specifically the speed–of the HMW drink.
For this very reason, it’s my belief that added amino-based nutrients should be kept to a minimum during ingestion of a HMW carbohydrate drink. My post workout recommendation for a 200 lb bodybuilder would be 75g of a HMW carbohydrate mixed with 5g creatine, 8g L-leucine, and 5-10g of BCAA’s. This meal should be followed, approximately 15-30 minutes later, with a meal containing protein and complex carbohydrates; preferably a fast-digesting liquid protein such as a whey isolate, and some complex carbohydrates.
If you understand the composition of muscle, you’ll see that there’s much more to it than just contractile tissue. Don’t forget the water, stored glycogen, minerals, blood vessels, and capillaries. By employing HMW carbohydrate powders, carbohydrate reserves can be quickly replenished, along with water and any other cell volumizing nutrients you consume along with it. Remember, faster glycogen restoration decreases catabolism and increases the rate of protein synthesis. And as an additional cosmetic benefit, the extra glycogen and water will create full, round-bellied, muscles that will be the envy of all your bodybuilding friends!