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? 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. 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). Therefore, in order for carbohydrates to be defined as anabolic, there must be conclusive evidence that carbohydrate ingestion increases skeletal muscle protein synthesis.
A common thread in bodybuilding thought is 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 affects of carbohydrates and insulin in mature adults? Does insulin have the same impact? Does it remain anabolic in mature adults?
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 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 synthesis (10) to determine the impact of the different macronutrient profiles.
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 & 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.
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 leucine, to a post workout recovery drink. 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.
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:
*30-50g whey protein
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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.
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, Vann RC, and O’Conner PMJ. (2002). Am J Physiol. 282: E880-E890.
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8. Ballard JF. (1982). Regulation of protein accumulation in cultured cells. Biochem J. 208: 275-287.
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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.