A person just needs to be smart about it and take the appropriate supplements and be aware of warning signs. The problem with this type of health decline I experienced with vegan patients is when it hits, it slams the wall and it all crashes in. People are absolutely blindsided by it and cannot figure out what went wrong. The bone fractures I think were the worst. Their bones would shatter and the surgical intervention necessary left them impaired.
The key I think is to not make demands on the body that the diet cannot keep up with. That I believe, was the biggest problem with these patients. They really thought they were super humans and pushed their bodies to the limits with extreme athletics and exercise routines. It literally broke them down because their diet could not keep up with the protein and antioxidants requirements for that kind of activity. Aging was accelerated and the conditions they suffered from were more age related chronic types of symptomology normally seen in older patients. I am not saying it can't be done. It is just that in my practice, I never saw it.