Carbs: The Anabolic Nutrient

Carbohydrates can help you pack on muscle — or bodyfat — depending on when, what and how much you eat. Here's what carbophobes and carboholics need to know about this important macronutrient for optimal physique gains.

By Dwayne N. Jackson, PhD | August 22, 2011

Carbs: The Anabolic Nutrient

Ask 10 bodybuilders about the importance of protein for muscle building and you’ll get unequivocal support. Ask the same group about the value of carbohydrates and you’ll likely get 10 different answers. 

Among the macronutrients, no other has faced more scrutiny than carbohydrates. In fact, over the years nutritionists and diet specialists have spoken out of both sides of their mouths about “carbs,” claiming they’re everything from beneficial (i.e., give you energy) to evil (i.e., make you fat) — a debate that leaves most of us confused about where carbs fit into a bodybuilding diet. 

There are several reasons for the confusion and contradictory advice. First and foremost, not all carbohydrate sources are created equal, and different forms of carbs cause several different reactions in the body. Second, research is only just starting to unravel the benefits and caveats of carbohydrate ingestion in its many different forms. As a serious bodybuilder, you understand how critical it is to find the right balance of protein, fats and carbohydrates in your nutrition plan. In this article, MuscleMag removes the question marks surrounding carbs with a comprehensive overview of the what, when and how for successfully including carbohydrates in your diet and supplement regimen, both to build muscle and lose bodyfat.

The Science of Carbs

Carbohydrates are so named because they’re made up of carbon, hydrogen and oxygen atoms (or hydrated carbon). These compounds serve many functional roles in the body beyond food energy. For example, ribose sugar comprises the backbone for the genetic RNA and is also important in the formation of many coenzymes. For the purposes of this article, however, we’ll focus specifically on carbohydrates as food or supplement sources for bodybuilders. 

For a fast-acting source of energy, carbohydrates trump both fat and protein because sugars are more easily and readily metabolized than the other macronutrients. The amount, type and rate of digestion of different carb sources dictate the level of blood glucose and amount of insulin released by the pancreas. Insulin is a hormone that delivers excess blood glucose to be stored in muscle cells and the liver as glycogen. 

Once glycogen levels are topped up, the remaining blood glucose is converted to fat and stored in fat cells. The fact that insulin is integral to driving nutrients into skeletal muscle makes it one of the most potent anabolic agents and the focus of many research studies in exercise science. Insulin sensitivity (the body’s ability to use insulin) greatly increases in trained individuals, especially right after training. In contrast, insulin sensitivity declines in the evening. 

Getting past all the science, the main point to deduce is that depending on the state of nutrition and timing of intake, high blood sugar and insulin levels could lead to either desirable or undesirable outcomes. Ideally you want to spike blood sugar and insulin levels at opportune times to take advantage of energy storage and anabolic effects while avoiding fat storage.


These are the simplest class of carbohydrates, as they can’t be hydrolyzed any further to form a simpler sugar. Simple-carb sources taste sweet and include glucose (dextrose) and fructose (fruit sugar). Glucose is absorbed high in the gastrointestinal (GI) tract and thus elevates blood sugar and insulin rapidly and greater than any other carbohydrate form. Fructose, on the other hand, digests low in the GI tract, has a relatively minor impact on blood sugar levels and is considered a slow carbohydrate.


These sugars are formed by the chemical combination of two monosaccharides. They also taste sweet and have a relatively fast absorption rate. Common disaccharides include lactose (glucose-galactose or milk sugar), sucrose (glucose-fructose) and maltose (glucose-glucose). Maltose elevates blood sugar very rapidly (in fact, it does so faster than glucose) and sucrose only moderately increases blood sugar, whereas lactose digests slowly and has a small impact on blood sugar.


These are carbohydrates formed by bonding several chains of monosaccharides and/or disaccharides. This form is commonly known as complex carbohydrates and includes starch, cellulose and glycogen. Starches are made up of multiple glucose units bonded together and are “plant sugars” produced by all green plants as an energy source. Common sources of starch are potatoes, wheat, corn and rice. Cellulose forms the structural components in plants and is relatively indigestible in humans — fiber is a form of cellulose. Most starches are considered medium- to slow-digesting, however, exceptions exist, one of which is waxy maize. The reason waxy maize absorbs so quickly is that it’s a modified high-molecular-weight cornstarch that has low osmolality, which enables it to bypass the stomach and get absorbed in the small intestines (causing a rapid rise in blood glucose).

The Glycemic Index

A common misconception is that all simple carbohydrates are fast sugars and all complex carbohydrates are slow sugars. This is definitely not the case; in fact, some complex carbohydrates (like maltodextrin) raise blood sugar and insulin levels rapidly, whereas a simple sugar like fructose has minimal impact on blood glucose. 

This variation is exactly why the glycemic index was created — to help you understand how different carbohydrate sources impact blood sugar. Using this tool is quite simple — all carbohydrate foods are ranked on a scale relative to glucose (a fast sugar, rated 100). Anything lower than 100 impacts blood sugar less than glucose and anything higher impacts it to a greater degree. 

For reliable glycemic index information or to search the database for specific food GI calculations, visit One important point to note is that fats, fiber and, in some cases, proteins can significantly slow the speed at which fast (high-glycemic index) carbs elevate blood glucose. Keep this in mind when employing the strategies outlined next.

Carb-Based Muscle-Building Strategy

There’s an abundance of scientific research supporting carbohydrate supplementation for muscle building. After exercise, muscle glycogen stores are depleted and insulin sensitivity is greatly increased, thus providing the perfect opportunity to spike insulin by ingesting fast carbohydrates like dextrose, maltodextrin or waxy maize. Not only does the boost in insulin increase glycogen repletion, but it also serves to carry amino acids and nutrients into damaged muscle cells. Several studies indicate that post-training carbohydrate and protein supplements boost the anabolic response, augment recovery and promote increased gains in lean mass.

To take advantage of these muscle-building benefits, you should drink a post-workout shake containing a 2:1 ratio of high-glycemic index (fast) carbohydrates and fast-absorbing protein. The best combination is dextrose or maltodextrin and whey protein hydrolysate or isolate. Individuals who are sensitive to dextrose or maltodextrin can use waxy maize as an alternate fast-carb source. If you opt for waxy maize, just make sure to take it 15–20 minutes before your protein powder, as its impact on blood sugar may be slowed when taken at the same time with protein. 

In any case (depending on your body mass), you should strive to ingest approximately 60–100 grams of fast-absorbing carbs and 30–50 grams of fast-absorbing protein as soon as you finish working out. In general, you should aim to consume 1–1.5 grams of protein per pound of bodyweight per day (divided into six doses throughout the day, with one being 30 minutes prior to training and one being immediately after training).

Carb Loading

Carb loading in bodybuilding is primarily used as a strategy to make muscles look fuller and skin appear tighter while onstage, during a photo shoot or whenever you want your physique looking its absolute best. 

There are numerous diet and workout strategies used for carb loading in bodybuilding, but the common goal among all approaches is to create an environment of glycogen super-compensation in skeletal muscle. This state is achieved by depleting glycogen stores by high-repetition, long-duration workouts for days under carbohydrate restriction. 

Once carbohydrate depletion is achieved, the diet switches to short-term, high-carbohydrate intake, during which the body restores glycogen in muscle to a higher level than before depletion. From a performance standpoint super-compensation provides more glycogen for subsequent exercise bouts, but (important for bodybuilding) it also results in an increase in muscle cell volume (cell volumization). This boost in cell volume occurs because each molecule of glycogen takes four molecules of water with it into the cell, resulting in less subcutaneous (under the skin) water and fuller-looking muscles, which give the body a leaner/harder appearance. 

Here’s an example of a carb-loading strategy: For 3–5 days, deplete muscle glycogen stores by decreasing your carbohydrate intake by 50% or more (replace calories by increasing your fat intake) and train using full-body, high-rep workouts. After glycogen depletion, double your original carb intake for the three days preceding your competition, photo shoot or special event. Since each individual responds differently to carb loading, you should experiment with this strategy in the offseason to know exactly how many days you need to deplete/super-compensate glycogen and look and feel your best.

Carb Cycling

This strategy aims at maintaining or building lean mass while losing bodyfat, as it combines the anabolism-boosting benefits of carbohydrate ingestion and the fat-burning advantages of low-carbohydrate diets. In the quest to get lean, many nutrition plans are centered on low-carb strategies to force the use of bodyfat for fuel. However, there are theories suggesting that staying on a low-carb diet for extended periods can lead to a decline in leptin levels. Leptin is a hormone that staves off hunger while simultaneously keeping your metabolic rate elevated. By going through alternating periods of low-carb and high-carb dieting, you can prevent drops in leptin levels, maintain hunger control and ensure your metabolism stays revved.

Carb cycling also provides a psychological advantage over strict low-carb diets. Knowing you’ll be able to eat carbs again in a few days makes getting through the low-carb days much more manageable. Another problem with strict low-carb diets is that they force you to limit fresh fruit and whole grains, two food sources that provide a number of health pluses like antioxidants and phytonutrients.

As you can see carbs serve a major role in bodybuilding, from bulking up to the final touches in your contest preparation. The key to using them effectively is to have a basic understanding of how they affect the body based on ingestion timing, amount and impact on blood glucose.

About the Author

Dwayne N. Jackson, PhD

Dwayne N. Jackson, PhD, is a professor and scientist in medical biophysics at one of Canada’s top medical schools, the University of Western Ontario. He has over 12 years of university education in physiology and has attended the University of Ottawa, the University of Western Ontario and the Yale School of Medicine. He also has over 20 years of competitive and recreational bodybuilding experience and is an expert in the areas of performance nutrition and supplementation.