What is an optimal ALT level?
The short answer
Optimal ALT is under 30 U/L, as stated on video.
Most labs call ALT high only above 55. So your report can call 43 normal while it sits above the optimal ceiling.
“now the general rule of thumb is that you would like to see an A and ALT both below about 30 IU per liter”
What each range means
- under 30 U/L Optimal
- 30–55 U/L Normal on most reports. Above optimal Dr. Peter Attia · 17:32 →
- over 55 U/L Most labs flag this as high
What ALT measures
An enzyme concentrated inside liver cells.
Stressed or damaged liver cells leak it into the blood. That makes it one of the most direct signals of liver strain.
Checked against MedlinePlus — ALT Blood Test.
Why it matters, on the record
“if your alt is High it usually means you have liver fat doesn't tell you why you have liver fat but it usually means you have liver fat”
Common questions
What is an optimal ALT level?
Under 30 U/L, from a quote on video (Dr. Peter Attia, 17:32).
What is a normal ALT level?
Most US labs print 0–55 U/L. Your report grades you against that range. It exists to catch disease, not to describe your best.
What does your ALT number mean?
On a typical lab range, up to 55 U/L is normal and over 55 is high. Your own report prints its range next to your number, and that is the one your lab uses. The optimal range on this page comes with the quote behind it.
Is ALT of 43 normal?
A typical lab range calls it normal. On video, the optimal ceiling is 30 U/L (Dr. Peter Attia, 17:32), so by that line it is high. Not every source agrees with that line.
Do the sources agree?
No. There is also a case for a different line: “the upper limit of alt should be 25 when I entered medical school in 1976 the upper limit for alt was 25” (Dr. Robert Lustig, 1:31:55)
What does the ALT test measure?
An enzyme concentrated inside liver cells. Stressed or damaged liver cells leak it into the blood. That makes it one of the most direct signals of liver strain.
Where the record disagrees
“the upper limit of alt should be 25 when I entered medical school in 1976 the upper limit for alt was 25”