ALT is an enzyme found mainly in the liver that helps the liver metabolise food into energy. Elevated levels of ALT in the blood can occur when the liver is damaged or diseased.

ALT levels are a poor predictor of non-alcoholic fatty liver disease (NAFLD) but is often elevated.

ALT is can be considered a biomarker or surrogate marker for degree of liver fat.

In 2011–12, around 1.9 million (11.0%) Australians aged 18 years and over had abnormal or elevated levels of ALT in their blood. Men were more likely than women to have elevated ALT (13.8% compared with 8.3%) [}

Abnormal liver function as measured by ALT is defined as: an ALT reading of greater than 40 U/L for males and greater than 30 U/L for females.

However, what is considered normal today, was abnormal just a few decades ago.

In a paper from 1972(1) healthy volunteers had the following levels:

  • Females 5-12 U/L
  • Males 5-19 U/L

In a paper from 1980 examining the effects of alcohol consumption on the liver enzymes, levels above 25 was considered abnormal for ALT (2).

So, in a few decades, the upper limit of “normal” has gone up from 25 to 40 U/L.

This is likely due to the fat that we all have fatty livers and so “normal” is now a fatty liver.

As healthcare practitioners we should help our patients to get to back to a level of ALT of 20 or below.

Apart from reducing alcohol and fructose consumption, fasting with the ProLon Fasting Mimicking Diet is an effective therapy for reducing elevated ALT.


1.         Wilkinson JH, Baron DN, Moss DW, Walker PG. Standardization of clinical enzyme assays: a reference method for aspartate and alanine transaminases. J Clin Pathol. 1972;25(11):940-4.

2.         Nakamura S. Alcohol, liver function tests, and high density lipoprotein cholesterol in university students. Tohoku J Exp Med. 1980;132(2):241-2.