My next interview was so upsetting that it is difficult to write about, and it shows that CR can, in certain cases, lead to full-blown anorexia. I called Al at home; his voice was quiet and somewhat difficult to hear. I asked how many calories a day he ate (1,950, he said) and how much he weighed."Ninety-two," he answered. I hoped I'd heard wrong. "How tall are you?" I asked. "Five-four," he said. "But I used to be 5-feet-11." He paused. "Osteoporosis." His spine had compressed a full 7 inches—or perhaps he was bent over. I was glad we were on the phone and I couldn't see him.
Al, who is 59, said he began CR in 1989 after reading about it in a textbook co-written by CR guru Roy Walford. -link
It is likely that the CR performed here was more extreme and has now become more moderate. Such examples suggest that extreme CR might not be recommendable for longer lived animals prone to bone loss over time.
More moderate CR, combined with CR mimetics should be viable and not entail such side effects(adequate calcium intake and vitamin k2 should probably also be helpful). Several CR mimetics are said to not be additive with maximal CR(around 65% restriction), but should likely have additive effect on more moderate CR. An interesting compound that should hopefully be tested in mammals, is rhodiola, which is a compound that is additive with CR and even maximal CR in a species of insect. The mechanisms of rhodiola are also of interest seeing as it can move some species' lifespan beyond maximal CR