We surely have some limit, we just can’t possibly know what our personal one is on our current diet (and level of fat adaptation or whatever may matter)… We change something and the results may be very off. If a scientist clearly shows that nature laws and some inevitable behavior of the human body has a pretty much fixed results in every case (except in very extreme cases, maybe), that’s fine but it’s usually not the case, our diet and personal factors have a too big impact on things. Just because they measure something in some circumstances, it may be totally different in others.
