Are Carbohydrates Anabolic?

There are probably more myths and speculation surrounding carbohydrates than any other macronutrient. Do they make you fat or not? Do you need them for energy or not? Do they increase performance or not?

How Do Macronutrients And Micronutrients Differ?

The four macronutrients are protein (source of amino acids), carbohydrates, lipids (fats), and water—all of which you need in plentiful (hence the term 'macro') amounts each day.

Micronutrients—mainly vitamins and minerals—are needed in relatively small amounts (hence 'micro'), and have been shown to be essential to growth and development, and for good health and winning athletic performance.

The focus of this article, however, is determining whether or not carbohydrates should be considered anabolic.

To determine this, we first must define what "anabolic" is. Simply, the definition of anabolic is "of or related to the synthetic phase of metabolism." The synthetic phase of metabolism that is referred to is protein synthesis, the process by which cells make new protein.

What Does Anabolic Mean?

Anabolic refers to the metabolic process that is characterized by molecular growth, such as the increase of muscle mass. Thus, it means "muscle-building" in most common bodybuilding contexts.

Briefly, some signal for growth (hormones, nutrients, etc.) causes an increase in the rate at which new proteins are synthesized within the cell. When this process occurs on a large scale over time in skeletal muscle, it is referred to as skeletal muscle hypertrophy (growth).

Hypertrophy Vs. Hyperplasia

Hypertrophy refers to an increase in muscle size, due to the enlargement of the size of the cells, as opposed to an increase in the number of cells (by cell division, a.k.a. Hyperplasia). Hypertrophy is most commonly seen in muscle that has been actively stimulated, the most well-known method being exercise.

Therefore, in order for carbohydrates to be defined as anabolic, there must be conclusive evidence that carbohydrate ingestion increases skeletal muscle protein synthesis.

Insulin's Role

A common thread in bodybuilding thought is that carbohydrates are anabolic because they increase insulin secretion, and insulin is anabolic. There are countless articles written on how insulin increases protein synthesis and decreases protein degradation, making it one of the most anabolic hormones in the body.

Many of these articles, however, base their conclusions on scientific research that was conducted using the wrong populations. You see, insulin is actually a growth hormone. This simply means that the body is most sensitive to the effect of the hormone during the growth process.

The main growing years for humans are from 0-18 years old, approximately. So when we are young, we are very sensitive to growth hormones such as insulin. Indeed, the research supports this as there are numerous studies showing insulin to increase protein synthesis and inhibit protein breakdown in young subjects at physiological (normal) concentrations.^1-4

But what about the effects of carbohydrates and insulin in mature adults? Does insulin have the same impact? Does it remain anabolic in mature adults?

Scientific Research

There is quite a bit of scientific literature covering the topic of insulin's impact in mature subjects. In fact, there are some studies that concluded that insulin is indeed anabolic in mature subjects.^5,6 These studies, however, were conducted using supraphysiological (above normal) concentrations of insulin that would never be achieved in the body by feeding even very high amounts of carbohydrates and calories.

These results are in accordance with anecdotal reports from bodybuilders that inject insulin regularly and claim it to be a very powerful anabolic agent. In mature subjects at normal physiological concentrations, however, insulin administration by itself appears to have little impact on protein synthesis or protein degradation.^7-9

Perhaps more conclusive is research conducted at the University of Illinois where subjects were exercised and given either placebo, a pure carbohydrate meal, or a complete meal containing carbohydrates, protein, and fat. The researchers then measured the rates of skeletal muscle protein synthesis¹⁰ to determine the impact of the different macronutrient profiles.

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The placebo meal and the carbohydrate-only meal did not stimulate protein synthesis to any significant degree. The complete meal, however, significantly increased the rate of skeletal muscle protein synthesis.

When one looks at this study, it becomes quite clear that carbohydrates alone will not stimulate protein synthesis and that the increases in protein synthesis observed from eating a meal are most likely due to the dietary protein content of the meal.

Now, I'm sure you are wondering, "Why eat carbohydrates at all, then? Why not just load up on as much protein as possible, since that is the anabolic component of a meal?" These are excellent points. Fortunately for us, the same researchers at the University of Illinois followed up their aforementioned experiment with another.

This time, subjects were exercised and either given a placebo, a pure carbohydrate meal, a pure leucine (the amino acid primarily responsible for the anabolic affect of dietary protein) meal, or a carbohydrate and leucine meal. The researchers then measured the rates of skeletal muscle protein synthesis.¹¹

They found that the pure carbohydrate meal had absolutely no impact on protein synthesis, but the meal containing leucine significantly increased protein synthesis.

Interestingly, they also found that the meal containing carbohydrates and leucine increased skeletal muscle protein synthesis to a greater degree than the protein-only meal. This seems to indicate that carbohydrates and amino acids, specifically leucine, have a synergistic effect on protein synthesis.

Great, How Can I Use This Information?

The next step is to take this information and translate it into a plan for the real world. How do we implement this information to help us in our never-ending quest for muscle growth? Quite simply, it is clear that a carbohydrate + protein drink is superior to either nutrient by itself.

Not only will a protein + carbohydrate drink be superior in terms of increasing protein synthesis, but it will also be superior for increasing glycogen replenishment, limiting protein breakdown, and enhancing recovery from exercise. It may also be useful to add the branched chain amino acid (BCAA) leucine to a post-workout recovery drink (PWO).

What Is Glycogen, And What Does PWO Stand For?

PWO refers to a 'Post-workout shake.

Leucine is the amino acid most responsible for the increase in protein synthesis that results from protein ingestion. In fact, a recent study published in the American Journal of Physiology examined the effect of different recovery drinks on skeletal muscle protein synthesis after a bout of resistance exercise.¹²

The mixtures included carbohydrate only, carbohydrate + protein, and carbohydrate + protein + leucine. The researchers found that the mixture containing carbohydrate + protein + leucine had a greater impact on skeletal muscle protein synthesis than the carbohydrate only and the carbohydrate + protein drinks.

The researchers believed this may be due to leucine providing a protein-sparing effect by decreasing the rate of protein breakdown and further stimulating protein synthesis.

Conclusion

In conclusion, though carbohydrates are not anabolic, they do have a synergistic effect on muscle protein synthesis when combined with dietary protein post-workout.

The optimal post-workout meal should be liquid to shorten digestion time and include a mixture of fast-digesting carbohydrates, a quick-digesting protein source, and possibly added leucine. You should consume this drink immediately post-workout for optimal results. My specific recommendations are:

• 50-75g Dextrose
• 30-50g Whey Protein
• 5-15g Leucine

References:

1. Garlick PJ, Fern M, and Preedy VR. (1983). The effect of insulin infusion and food intake on muscle protein synthesis in postabsorptive rats. Biochem J. 210: 669-676.
2. O'Conner PMJ, Bush JA, Suryawan A, Nguyen HV, and Davis TA. (2003). Insulin and amino acids independently stimulate skeletal muscle protein synthesis in neonatal pigs. Am J Physiol. 284: E110-E119.
3. O'Conner PMJ, Kimball SR, Suryawan A, Bush JA, Nguyen HV, Jefferson LS, and Davis TA. (2003). Am J Physiol. 285: 40-53.
4. Davis TA, Fiorotto ML, Burrin DG, Reeds PJ, Nguyen HV, Beckett PR, Vann RC, and O'Conner PMJ. (2002). Am J Physiol. 282: E880-E890.
5. Ballard JF and Francis GL. (1983). Effects of anabolic agents on protein breakdown in L6 myoblasts. Biochem J. 210: 243-249.
6. Fulks RM, Li JB, and Goldberg AL. (1975). Effects of Insulin, Glucose, and Amino Acids on Protein Turnover in Rat Diaphram. J. Biol Chem. 250: 290-298.
7. McNurlan MA, Essen P, Thorell A, Calder AG, Anderson SE, Ljungqvist O, Sandgren A, Grant I, Tjader I, Ballmer PE, Wernerman J, and Garlick PJ. (1994). Response of protein synthesis in human skeletal muscle to insulin: an investigation with L-[2H5]phenylalanine. Am J Physiol. 267: E102-E108.
8. Ballard JF. (1982). Regulation of protein accumulation in cultured cells. Biochem J. 208: 275-287.
9. Gulve EA and Dice JF. (1989). Regulation of protein synthesis and degradation in L8 myotubes. Biochem J. 260: 377-387.
10. Gautsch, T.A., Anthony, J.C., Kimball, S.R., Paul, G.L., Layman, D.K. & Jefferson, L.S. (1998) Availability of eIF4E regulates skeletal muscle protein synthesis during recovery from exercise. Am. J. Physiol. 274: C406-C414.
11. Anthony, J.C., Gautsch-Anthony, T. & Layman, D.K. (1999) Leucine supplementation enhances skeletal muscle recovery in rats following exercise. J. Nutr. 129: 1102-1106.
12. Koopman R, Wagenmakers AJM, Manders RJF, Zorenc AHG, Senden JMG, Gorselink M, Keizer HA, and van Loon LJC. (2005). Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects. Am J Physiol. 288: 645-653.