Past a point, the body stops burning off extra leucine
Healthy young men were fed leucine up to 25 times the daily requirement. Their capacity to burn it off topped out at 550 mg per kilogram a day; ammonia rose above 500.
What the study found
Above 500 mg of leucine per kilo a day, ammonia started climbing
Healthy young men were fed leucine from the average daily requirement up to 25 times it. Their ability to burn off the excess reached its ceiling at 550 mg per kilogram of body mass a day, and blood ammonia began rising above 500. Nobody reported any gut trouble at any dose tested.
The caveat · Number of men never stated
The abstract never says how many men took part, which is the first thing you would want from a dose-response study. The adverse signal is a blood chemistry change, not a symptom anyone reported. Healthy young men, fed briefly, so nothing here reaches long-term intake.