Truth is, it appears to be both. Per usual, too much appears a negative, too little, also a negative
Supplement companies are constantly pushing mTOR as the magic pathway to building muscle, and various net guru type talk about keeping mTOR activated, with heavy marketing of Leucine, BCAA, etc. to keep mTOR activated. It’s unlikely that keeping an anabolic pathway such as mTOR active is a path to longevity. It’s interesting to note, cancer researchers, anti aging researchers, etc are looking for ways to limit/control mTOR.
Here’s an article on the topic by a researcher in the field worth a read. Obviously, it’s far from conclusive at this time that healthy people intentionally activating mTOR to assist in altering bodycomp etc, but it’s also not difficult to fathom that pathways also responsible for cellular growth, cell division, etc being activated constantly could have long term repercussions. We need mTor and too little also also clearly a negative, and like growth factors such as IGF-1 the risks/benefits will appear as a U shaped graph, where too much or two little increases the risks for various pathology best avoided (1). Interestingly, drugs that lower mTOR have been found to increase life span of some animals for example.
Bottom line is, pumping leucine into the system (as an example of a supplement, along with BCAAs, etc that are mTOR activators) all the time in an attempt to drive mTOR may be a bad idea long term in my view, but more data is clearly needed, so don’t freak out. I did however want to present the other side of mTOR and related topics/pathways. From the article linked below:
“There’s evidence that both too much mTOR activity and too little mTOR activity is a problem and it happens in different diseases.
For example, too much mTOR activity is clearly connected to certain types of cancers and neurological diseases, particularly epilepsy and there’s some evidence even for autism. Too little mTOR activity is connected to diseases such as atrophy of the muscle in certain situations, even aging a certain cell.
However, what is less well understood, is why those changes in mTOR activity have those effects. There are some big processes downstream of mTOR like autophagy which is our self-eating, as well as protein synthesis that is regulated by it, which are likely interconnected to all these diseases.”