From a health standpoint, if you are getting all your necessary nutrients from the allowed foods and you supplement anything you may be missing, there should be no harm caused by the alkaline diet. Most of the foods allowed are healthy (certain fruits, vegetables, tubers, nuts and legumes, whey protein, etc.) but some of the foods disallowed are also healthy like lean meats/fish, grains, etc. Therefore you will need to be very careful in assembling your daily diet to make sure you are getting all you need to maintain health as you age. From a long term palatable standpoint, well, that’s up to the individual, but the diet looks extremely difficult to sustain. And finally, there is no scientific support for any of the diet’s claims, but if you feel better and get all your daily nutrients, there is no reason you would hurt yourself long term.