You seem to have missed the part where many of the same mechanisms exist in animals, and have been examined with a multitude of randomized trials. For example, the link between higher protein consumption and reduced longevity. I see a lot of denial on this subject because guys are all about building big muscles at any cost.Epidemiological studies are unfortunately a horrible way to assess anything diet related. ...
The ability of protein/amino acid restriction to extend rodent longevity is linked to a reduction in the levels of IGF-1, in agreement with the role of pro-growth signaling in blunting longevity in organisms ranging from yeast to mice (Figure 2) (Longo et al., 2021). In humans, [calorie restriction] results in beneficial changes in cardiometabolic risk factors but is not associated with reduced IGF-1 levels unless participants are also protein restricted (Fontana et al., 2008). In both mice and humans, a low-protein diet imposes a reduction in growth factors/signaling both upstream of IGF-1 (GHRH, GH) and downstream of it (mTOR, S6K). With [protein-restricted] diets, lower growth signaling goes hand in hand with lower insulin and improved insulin sensitivity, and although clinical studies more often focus on insulin, it is clear that there is a connection between these pathways.
The role of protein intake in increasing mortality and reducing longevity appears to be also conserved in humans, although this relationship is complex. There is evidence that diet should be tailored to age. Whereas consumption of more than 20% of calories in the form of proteins is associated with a 75% increase in overall mortality risk and 400% increase in the risk of cancer mortality in subjects 65 years old or younger compared to consumption of less than 10% of calories from proteins, these associations are not observed in those 66 and older (Levine et al., 2014). These results are in agreement with those in mice in which, prior to 85 weeks of age, mortality is minimized by a low protein consumption, but as animals aged beyond 85 weeks, a major increase in the protein to carbohydrate ratio is necessary to minimize mortality (Senior et al., 2019).