40 g of protein per day is only 6.1 oz of chicken tenderloins (raw weight) per day which is very unlikely to cause the effect described in the paper ("hyperfiltration and increased urinary calcium excretion which can, in turn, lead to chronic kidney disease development").

People who eat a lot of protein die sooner than people who eat less, but that is probably because plentiful protein prevents the body from entering a state called "autophagy". Intentionally inducing autophagy for 5 days every other month (by using Valter Longo's protocol) while eating plenty of protein the rest of the time is probably better for most people than a consistently low-protein diet as long as one is avoiding red meat (provided the people can afford the protein which will be the case for almost everyone in the developed world).