Fatty Liver in Athletes: Causes and Links to Training and Drugs
Fatty liver disease is usually associated with inactivity and obesity, so finding it in a regular gym-goer can come as a surprise. Yet it does occur in active people, sometimes linked to diet, alcohol, body composition goals or performance-enhancing drugs. Our editorial team explains the causes, the pitfalls in testing and the role of exercise in prevention and treatment.
What fatty liver is
Fatty liver means excess fat stored inside liver cells, typically more than about five per cent of liver tissue. In 2023 international liver societies agreed new terminology: what used to be called non-alcoholic fatty liver disease (NAFLD) is now metabolic dysfunction-associated steatotic liver disease, or MASLD.
The name change reflects the fact that the condition is driven mainly by metabolic factors such as insulin resistance, abdominal fat, high blood pressure and abnormal blood lipids. When significant alcohol use also contributes, the term MetALD is used.
Most people with simple fatty liver feel well. In a minority, the fat triggers inflammation (steatohepatitis), which can progress to scarring (fibrosis) and eventually cirrhosis. Fibrosis, rather than the amount of fat, is the main predictor of long-term liver outcomes.
In the UK, MASLD is estimated to affect a large proportion of adults, and it is one of the most common reasons for abnormal liver blood tests in primary care. NICE guidance recommends assessing fibrosis risk rather than simply recording fat on a scan.
Why athletes are not automatically protected
Regular exercise lowers the risk of MASLD, but it does not make anyone immune. A person can train hard and still have a diet very high in refined sugar and alcohol, or carry a large amount of visceral fat despite good muscle mass.
Weight-class and physique athletes often go through repeated bulking and cutting phases. Rapid weight gain on a calorie surplus, especially one rich in fructose and saturated fat, can increase liver fat within weeks. Very rapid weight loss can also temporarily worsen liver inflammation in some people.
Genetics plays a role. Variants in genes such as PNPLA3 make some people more prone to liver fat at any body weight. This partly explains why fatty liver is sometimes found in lean individuals.
Alcohol remains a key factor. Post-match drinking culture, combined with dehydration and inadequate food, places extra stress on the liver. UK low-risk guidelines advise no more than 14 units per week, spread over several days.
Performance-enhancing drugs and the liver
Anabolic-androgenic steroids are well known for liver toxicity, particularly the oral 17-alpha-alkylated compounds. These are associated with cholestasis (impaired bile flow), peliosis hepatis (blood-filled cysts) and liver tumours, including adenomas.
A Brazilian study by Schwingel and colleagues published in 2011 found a high prevalence of fatty liver among male bodybuilders using anabolic steroids, even without obesity. The authors proposed that steroids could be a risk factor for toxicant-associated fatty liver disease.
Steroids also disturb blood lipids, lowering HDL and raising LDL, and may promote insulin resistance during and after use. Growth hormone misuse can raise blood glucose. Both effects favour fat accumulation in the liver.
Other substances can harm the liver too. High-dose green tea extract, some multi-ingredient fat burners and certain herbal products have been linked to drug-induced liver injury. Our editorial team does not provide guidance on using performance-enhancing drugs; anyone who has used them should tell their doctor so that tests can be interpreted correctly.
Testing pitfalls: exercise and liver enzymes
Liver blood tests can be misleading in people who lift weights. ALT and AST, the enzymes most often used to flag liver damage, are also present in muscle. A hard training session can raise them for several days.
A solid starting point is methandienone tabletten.
Pettersson and colleagues showed that healthy men performing a single intense weight-training session developed ALT and AST levels that would normally prompt liver investigations. Creatine kinase, a muscle marker, rose in parallel, confirming the muscular source.
| Test | What it shows | Exercise effect |
|---|---|---|
| ALT | Liver cell injury (also present in muscle) | Can rise for days after intense training |
| AST | Liver and muscle injury | Often rises more than ALT after exercise |
| GGT | Bile duct and liver stress, alcohol | Little affected by exercise |
| Creatine kinase (CK) | Muscle damage | Rises sharply after hard or unaccustomed sessions |
| FIB-4 / ELF test | Estimated risk of liver fibrosis | Used by GPs to decide on referral |
For this reason, doctors may ask you to avoid heavy training for several days before a liver test, and to report recent sessions. Measuring GGT and CK at the same time helps distinguish muscle from liver sources.
Imaging, usually ultrasound, can detect moderate or severe fat. To estimate fibrosis, UK pathways typically use the FIB-4 score from routine blood tests, followed by the ELF blood test or transient elastography (FibroScan) for those at intermediate risk.
What helps: training, diet and medical care
Exercise is one of the best-supported treatments for fatty liver. A meta-analysis by Keating and colleagues found that exercise reduces liver fat even with little or no weight loss. Johnson and colleagues demonstrated reduced liver and visceral fat after aerobic training without changes in body weight.
Both aerobic and resistance training appear helpful; consistency matters more than the exact format. Combining exercise with modest weight loss of around 7–10 per cent in those with excess weight produces the greatest improvement in liver inflammation and fibrosis.
- limit sugary drinks and foods high in added fructose;
- keep alcohol within UK low-risk guidelines, or avoid it entirely if liver tests are abnormal;
- favour a Mediterranean-style pattern rich in vegetables, legumes, fish, olive oil and whole grains;
- avoid extreme bulking phases and very rapid weight cuts;
- stop any non-prescribed hormones or "liver-heavy" supplements and tell your doctor about them.
There is growing interest in medicines for MASLD, including resmetirom and GLP-1 receptor agonists, but these are prescribed only after specialist assessment. Supplements marketed as "liver detox" products have little evidence and can occasionally cause liver harm themselves.
Regular follow-up matters. People with fatty liver and risk factors for fibrosis should have their FIB-4 score repeated at the intervals their GP recommends, typically every few years, and sooner if new risk factors appear.
Conclusions of the editorial team
Fatty liver, now called MASLD, can affect active people when diet, alcohol, genetics, rapid weight change or drug use outweigh the protective effect of training.
Anabolic steroids, particularly oral forms, are linked to liver damage and possibly to fatty liver itself. Disclosing their use to a doctor is essential for safe care.
Hard training can raise ALT and AST and mimic liver disease, so tests should be timed and interpreted with care, ideally with CK and GGT measured alongside. Regular exercise and a balanced diet remain the cornerstone of treatment.
Related reading includes our editorial guides on interpreting liver function tests, alcohol and recovery, and the cardiovascular effects of anabolic steroids.
References
- Rinella ME, Lazarus JV, Ratziu V, et al. A multisociety Delphi consensus statement on new fatty liver disease nomenclature. J Hepatol. 2023;79(6):1542–1556.
- European Association for the Study of the Liver (EASL), European Association for the Study of Diabetes (EASD), European Association for the Study of Obesity (EASO). EASL-EASD-EASO clinical practice guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD). J Hepatol. 2024;81(3):492–542.
- Pettersson J, Hindorf U, Persson P, et al. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol. 2008;65(2):253–259.
- Keating SE, Hackett DA, George J, Johnson NA. Exercise and non-alcoholic fatty liver disease: a systematic review and meta-analysis. J Hepatol. 2012;57(1):157–166.
- Johnson NA, Sachinwalla T, Walton DW, et al. Aerobic exercise training reduces hepatic and visceral lipids in obese individuals without weight loss. Hepatology. 2009;50(4):1105–1112.
- Schwingel PA, Cotrim HP, Salles BR, et al. Anabolic-androgenic steroids: a possible new risk factor of toxicant-associated fatty liver disease. Liver Int. 2011;31(3):348–353.
- National Institute for Health and Care Excellence. Non-alcoholic fatty liver disease (NAFLD): assessment and management. NICE guideline NG49. London: NICE; 2016.
