Elevated ALT and AST: when to worry about your liver
ALT and AST are called liver enzymes, but they are also found in muscle, especially AST. After an intense workout they can rise several-fold with no liver disease at all. If the rise persists, a common cause is fatty liver, and the main thing that helps it is weight loss.
Why ALT and AST go up after exercise
Intense exercise causes tiny injuries in muscle, and some enzymes leak from muscle cells into the blood. AST usually rises more than ALT, and the values can be several times above normal.
A 2008 study confirmed this: in healthy men, AST and ALT stayed elevated for at least a week after weight training, and the source was muscle, not the liver (Pettersson et al., British Journal of Clinical Pharmacology). If nobody knows about the recent workout, the result is easy to mistake for liver disease and leads to unnecessary tests.
How to prepare for a liver blood test:
- skip intense workouts for 48–72 hours before the test;
- don't go to the lab straight from the gym;
- count unusual exertion too: a long hike, running, CrossFit, weight training.
Fatty liver (MASLD): what it is and what helps
Fatty liver is fat building up in the liver; its current name is MASLD, metabolic dysfunction-associated steatotic liver disease. The 2024 European guidelines (EASL–EASD–EASO) recommend looking for it in people with excess weight, type 2 diabetes or other metabolic risk factors, abnormal liver tests, or signs of fat in the liver on ultrasound.
Lifestyle is the foundation. The same guidelines give weight-loss targets:
- 5% or more — less fat in the liver;
- 7–10% — less inflammation;
- 10% or more — improvement in fibrosis.
Add diet, movement and no alcohol. The guidelines mention coffee as good for the liver. How much damage the liver already has is assessed step by step: first a score calculated from blood tests, then elastography (FibroScan).
What else is linked to fatty liver
A lot is written about vitamin D and choline in fatty liver: people with the condition are often low in them. But there's no evidence that supplements treat the liver by themselves, and the 2024 European guidelines don't list them as treatment. The basis is weight loss, diet and physical activity. Choline is easy to get from ordinary food: eggs, liver, soy.
Alcohol-free beer is not a harmless swap: a 2022 study found that even without alcohol it increases visceral fat and liver fat, probably because of sugars and malt (The American Journal of Clinical Nutrition). 0% alcohol doesn't mean 0% harm.
High bilirubin: Gilbert's syndrome
Gilbert's syndrome is not a disease but rather a variant of normal. The enzyme that processes bilirubin in the liver works about 30% slower, so blood tests show raised indirect (unconjugated) bilirubin. It's a genetic trait, not related to liver disease, alcohol or lifestyle.
At most, the skin or eyes turn slightly yellow during stress, fasting, an infection, dehydration or heavy exertion. The liver is not being damaged. Gilbert's syndrome needs no treatment, but doctors should know about it when choosing certain specific medicines, such as some cancer drugs.
Liver cyst on ultrasound
A simple liver cyst is a small sac of fluid, usually present since birth, that just happened to show up on an ultrasound. It's not a parasite or a tumour and is usually harmless.
"Simple" means one chamber, smooth walls and clear contents. If the ultrasound shows septa, thickening or calcifications, that's a reason for a CT or MRI. If the cyst causes no symptoms, it needs neither treatment nor follow-up. If it's large and presses on nearby organs, causing heaviness on the right side or feeling full quickly, it's removed with a minimally invasive procedure.
When to see a doctor in person
- your skin or the whites of your eyes turned yellow, especially without an obvious reason like fasting or stress;
- your urine got dark or your stools got pale;
- your belly got bigger or your legs started to swell;
- ALT and AST are elevated again, even though you didn't exercise before the test.
Sources
- Pettersson J. et al. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol, 2008
- EASL–EASD–EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD), 2024
ALT, AST or bilirubin came back high and you're not sure what to do next? Let's go through your results together.