The liver is the main “chemist” in our body. It is the primary location for the conversion of one compound to another. Because of this, the liver can be thought of as the body’s detoxifier. If you have a liver, there is no need to “detox” through juice cleanses or lengthy fasts. Your liver does that for you every day.
The other 3 markers included in our liver group are enzymes that initiate or support the many detoxifying, energy producing, and overall housekeeping reactions that keep our bodies functioning.
- ALT = alanine transaminase
- AST = aspartate transaminase
- GGT = gamma-glutamyl transpeptidase
All of the markers are found in large quantities in the liver and can be elevated in the blood when there is liver damage; however, they are also present in other tissues. While GGT is fairly specific to the Liver, ALT and AST are also found in significant quantity in skeletal muscles. When muscle is damaged, such as in response to exercise, AST and ALT are released from the muscle and their concentration in the blood increases. In an athletic population, it is understandable that these markers may be elevated on routine blood tests.
ALT and AST can remain elevated for 7 or more days after strenuous exercise. The higher the intensity and the longer the duration of workout will result in higher peak levels and levels remaining high for longer. Untrained athletes will see larger and longer increases relative to more trained athletes.. As an athlete trains, their work capacity increases, allowing them to sustain greater training loads/volumes with a comparable increase in ALT, AST and CK. While resistance training generally causes greater muscle damage than endurance events, high levels of muscle damage can also be inflicted in ultra-endurance races and events, particularly those with larger or numerous changes in elevation. At Insidetracker, we have found that trail runners, road cyclists and mountain bikers are more susceptible to these types of elevations. Creatine Kinase, an enzyme found in our muscles, is another marker of muscle damage that follows the same pattern as AST and ALT after strenuous exercise. Adequate protein intake after strenuous exercise is required to repair the damage.
The general pattern of increases in aspartate transaminase (AST), alanine transaminase (ALT), and Creatine Kinase (CK) in response to muscle damage.
Some added insight
Because we know it can be alarming to have elevated liver markers, we’ve added new paragraphs for the liver group to help you better interpret your results. Now, when you view your liver group, your paragraph will inform you whether or not muscle damage may be skewing the results of your liver enzymes based on your CK.
Monitoring your levels for overtraining
Monitoring the levels of your AST, ALT, and CK throughout training can help you determine if your muscles are recovering as they should be. Prolonged elevations in any of these markers can mean that your training load is high, recovery is taking longer, and the risk of overtraining may be greater. Alongside these biomarkers, Testosterone and cortisol provide additional context into one’s training, particularly the T:C and fT:C ratios as these are often used as a metric of recovery and non-functional over-reaching Testosterone is important for both males and females, as it help to build and repair muscle. Declining levels of testosterone may be a red flag for impaired levels of muscle repair. Similarly, cortisol can be elevated as training continues. As stress related to workout frequency, intensity, and calorie demand increases throughout a season, cortisol levels slowly increase as well. Cortisol uses muscle and fat as substrate to provide a constant source of glucose in case of “emergency”.
What about GGT?
Unlike AST and ALT, GGT is not found in the muscle (although it is in other tissues). Elevated GGT cannot be attributed to muscle damage—unless the damage is so severe that other organs are being negatively affected. GGT is a more specific marker of overall liver health. Elevated levels can be caused by alcohol, medications (including chronic Tylenol use), and unhealthy lifestyle. In fact, GGT is associated with all the biomarkers you want to keep in the optimal zone. When looking at our users, elevated GGT is associated with elevated glucose, LDL, hsCRP, and triglycerides and with low HDL and vitamin D.
Some tips for keeping GGT levels within the optimal range:
- Drink alcohol in moderation (1 drink per day for women and 2 drinks per day for men)
- Use over-the-counter pain relief sparingly
- Engage in moderate aerobic activity or HIIT
- Follow a healthy diet within your calorie needs that is high in fiber and low in saturated fat and added sugars
- Maintain a healthy weight
Want to maximize your rest day? Download this FREE checklist to help optimize recovery on your day off.
Ashley is the Lead Nutrition Scientist at InsideTracker. As a registered dietitian and educator, Ashley enjoys cooking and teaching individuals the power that food has on their health. You’ll find Ashley hiking, eating, and spending time with her family. Follow her on Instagram @lower.cholesterol.nutrition.
Ashley Reaver, MS, RD, CSSD
 Ammar, Achraf, et al. "Temporal specificity of training: intra-day effects on biochemical responses and Olympic-Weightlifting performances." Journal of sports sciences 33.4 (2015): 358-368.
 Hazar, Muhsin, et al. "Effect of increasing maximal aerobic exercise on serum muscles enzymes in professional field hockey players." Global journal of health science 7.3 (2015): 69.
 Rosales, Xiomara Q., et al. "Fidelity of gamma-glutamyl transferase (GGT) in differentiating skeletal muscle from liver damage." Journal of child neurology 23.7 (2008): 748-751.
 St George, Alexis, et al. "Effect of a lifestyle intervention in patients with abnormal liver enzymes and metabolic risk factors." Journal of gastroenterology and hepatology 24.3 (2009): 399-407