Contributed by Damian Rodriguez, DHSc, MS
Recent research suggests that intense exercise may result in levels of liver enzymes well above normal reference ranges; both immediately (for more than a week) and (to a lesser extent) long-term. Communicate with your medical provider about your exercise regimen and consider taking time off from training if you know you will be soon undergoing a metabolic blood test.
As a component of your annual physical, whether you are in perfect health or have a chronic condition, your physician may suggest you take a comprehensive metabolic panel. After a quick blood draw, your serum will be transported to a lab where it will be tested for various markers of blood glucose regulation, electrolyte and fluid balance, and the functioning of the vital organs (including the liver). While alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyltransferase (GGT) may not mean much to you, they mean a lot to your overall health, as they provide your trusted medical professional with important data to evaluate the functioning of your vital organs—a crucial piece in the puzzle that is your health. But they are only a piece of that puzzle, and every individual’s puzzle is unique. Interestingly, recent research suggests that some lifestyle behaviors associated with high levels of fitness, especially high intensity exercise, may result in biomarkers most often associated with abnormal liver function.
Residing on the right side of your belly, the reddish-brown liver is one of the most vital of the vital organs. The liver works in conjunction with the gallbladder, pancreas, and intestines to digest, absorb, and process food, with its primary role serving as the body’s filter, detoxifying blood coming from the digestive tract before circulating it throughout the rest of the body. The liver also significantly influences weight management, fitness, and athletic performance, as it helps convert ingested carbohydrates into stored energy (glycogen), convert stored energy into usable energy (glucose), break down fat so it can be used as fuel, and plays a role in hormone production.
In short, if your goals include a lean and athletic body, a properly functioning liver is essential. The easiest and least invasive way to determine the health of your liver is through blood serum levels of specific liver enzymes. Enzymes are catalysts. Their existence within our body helps speed up chemical reactions, aiding in biological processes from digestion to metabolism. When investigating liver function, metabolic panels conventionally measure the blood serum levels of three specific enzymes: ALT, AST, and GGT.
ALT and AST
ALT and AST are liver enzymes that play a role in the conversion of amino acids. Found primarily within the liver, ALT is released into the bloodstream as a response to damage or inflammation. The liver contains high concentrations of AST, but smaller amounts are also present within the heart, kidneys, brain, and even muscle tissue. High levels of ALT directly signify injury to the liver, while the origin of elevated AST levels is more difficult to discern. Research suggests that levels of both enzymes can more than double following a strenuous workout and remain increased for over a week1,2. Another study involving 60 college-level soccer players showed that ALT levels were significantly elevated (compared to pre-workout levels) due to a single high intensity workout, although there was no real hepatic cell damage3. Furthermore, one case reported an otherwise healthy man whose metabolic panel exhibited levels of ALT and AST nearly double the normal accepted thresholds while he was undertaking a new exercise program, but a liver biopsy and FibroScan® determined no liver damage, and enzyme levels normalized after fully recovering from exercise4. It is unlikely that intense exercise will result in ALT and AST levels spiking to more than twice the upper threshold of reference ranges2.
Concentrated predominantly in the liver, but also found in the other digestive tract organs, GGT is a transport enzyme. It helps shuttle other molecules throughout the body, assisting the liver in filtering out toxins and metabolizing drugs. Elevated levels of GGT in the blood usually indicates a liver that is not functioning effectively and is having difficulty filtering out possibly toxic foreign substances. Unlike ALT and AST, GGT is not found within muscle tissue, so increased levels are rarely caused by muscular damage. This makes GGT a more direct indicator of liver health. While the breadth of research suggests that GGT is not as likely to immediately increase due to exercise-induced muscular damage as other liver enzymes, there are clinical examples of high-intensity exercise elevating GGT levels for extended periods of time with no corresponding liver impairment4,5. Although generally GGT levels are not significantly influenced by exercise, they can vary over 15 percent from day to day based on several factors. If your initial numbers exceed the current guidelines, consider taking a training hiatus for a week and retesting.
Along with ALT, AST, and GGT, a comprehensive metabolic panel may also include assessments of blood serum levels of alkaline phosphatase (ALP), blood urea nitrogen (BUN), creatinine, creatine kinase, ferritin, and other enzymes that are conventional biomarkers of liver and overall digestive tract health. Research suggests that all aforementioned biomarkers may be influenced by intense exercise2. If you’ve had a strenuous workout in the last week, you will more than likely have abnormal blood test results. If lifting heavy things and pushing your heart rate to its max are part of your lifestyle, it is almost inevitable that your liver enzymes levels will be chronically elevated, but that isn’t necessarily cause for concern.
The reality is that exercise changes your body from the inside out, and metabolic panel reference ranges are developed with the average person in mind. When undertaking a new (high intensity) exercise program or altering your normal diet, especially if it includes increased protein intake, it is important to monitor liver health. But also be aware that a metabolic panel may not paint a clear overall picture. Communicate with your physician about your active lifestyle so they can develop some context of how blood test results are relevant to you. Also consider dialing down the intensity for a few days (or an entire week) if you know you will be undergoing blood tests, so that the results may provide a more accurate picture of your health.