The Cahill Cycle. What it Means for Runners, Cyclists, and Other Racers

So who is this Cahill, and what is his cycling workout like? Well his full name is George Cahill, but he was no cyclist. Well, maybe he was, I don’t know, but I do know that he was the scientist that discovered the glucose-alanine cycle, which earned his namesake. While George may not have a workout for you, you probably use the Cahill Cycle more than you think.

Amino Acids Become Glucose

Supplements for Runners

The human body is an amazingly adaptive organism. Throughout our evolution, we undoubtedly went through periods of time when we could not find enough carbohydrate-containing foods to fuel all of our activity. Our adaptation was to make new glucose from the carbon skeletons of triglycerides (fat) and amino acids (protein), like glutamine and alanine.

Low-carbohydrate diet is a relative term, however. We may need to utilize amino acids for fuel during periods of starvation and dietary carbohydrate restriction, yes, but we may also very well need to make new glucose when we have very high glucose demands. For most of you reading, that time is exercise. Therefore, a low-carbohydrate diet may be more appropriately defined as one that lacks carbohydrate in quantities required by exercise.

All but 2 amino acids (leucine and lysine) can be converted to glucose. However, alanine is the first to go due to its structural similarities with glucose. It is actually oxidized all the time, even at rest, just at very slow rates.

The Cahill Cycle

Nutrition for Runners

When we metabolize glucose at very high rates during intense exercise, we generate more end-product (pyruvate) than we can handle. Pyruvate is then converted to lactate, and that is why you feel “muscle burn” – you’re working harder than your metabolism can keep up with. Cahill’s buddy, Cori, found that lactate is converted back to pyruvate, which is converted back to glucose, in the liver. Concurrently however, pyruvate can also be converted to alanine; you just don’t feel it like you feel lactate. Remember, the human body is just a highly organized structure of elements and every reaction is not caused by some sort of deliberate intent, molecules are just bouncing around, bumping into each other, and reactions occur by chance. The chance increases with the amount of reactants (in this case, pyruvate) present in the system (in this case, muscle, blood, and/or liver).

Alanine does the same thing as lactate – it can be made from pyruvate and go to the liver to become glucose. Also, we have tons of alanine stored in muscle proteins, which can be released to make glucose as well. Whether generated from pyruvate or from breaking down muscle tissue, alanine goes to the liver, gets converted to pyruvate, which is then converted back to glucose, which makes its way back to the muscles to be used up all over again. That’s the Cahill Cycle.

Should Athletes Supplement Alanine

Nutrition for Runners

Alanine would not be a primary supplement concern for athletes unless they’re going through periods of prolonged fasting. However if one is fasting, can you even consume alanine without breaking the fast? Not a primary consideration, alanine may be a secondary or tertiary consideration for endurance athletes. It would be secondary if the athlete is consuming a low-protein diet or if the athlete has very high energy demands. Alanine would be tertiary if the athlete is consuming enough protein alongside high energy demands.

In both the secondary and tertiary options, alanine would be best supplemented near exercise to help prevent the breakdown of muscle tissue that would occur for the purposes of using muscle proteins for generating glucose. SustainElite contains 300mg of alanine for exactly this purpose.

Alanine production from the breakdown of muscle protein occurs pretty early during exercise. Even with adequate protein intake (1.5 grams protein per kg body weight per day), 90 minutes of exercise at only 45% maximal oxygen consumption doubles the rate of muscle protein breakdown so alanine can be used to make glucose. Supplementing alanine before or during exercise can prevent extensive breakdown of muscle tissue, and with consistent use, speed recovery, maintain muscle health, and make each training session stronger. Let’s face it, we demand a lot from our muscles and should repay them for all of their work.

Final Word on Alanine Supplementation for Athletes

Sports Drink for Runners

We’re not going to say you need alanine just because it’s in our sports drink. At some time or another, you may actually need the carbohydrates that are in the sports drink, but that’s another story. Alanine is just one of the many facets of SustainElite that make it the best sports drink. After all, that’s what we want, right? To be the best that we can be? Alanine and a few other amino acids are key in potentiating long-term performance as well as performance on race day if the race is going to take 1.5 hours or more. If you’re looking for an edge, and already consuming appropriate amounts of carbohydrate and protein, consider adding alanine during exercise to jump start the recovery process.


Carraro, F., Naldini, A., Weber, J. M., & Wolfe, R. R. (1994). Alanine kinetics in humans during low-intensity exercise. Medicine and science in sports and exercise, 26(3), 348-353.