Sugar consumption has been steadily declining since the 90s or at least very early 2000s, yet the disease statistics are climbing. Almost everyone has metabolic syndrome. Back in 1950s, and in France till recently, people ate fat and carbs without much diseased states. Keto and carnivore diets are not only new and fitting under a fad, but they are indeed proven to be harmful in the medium to long run. Look up the studies yourself, particularly regarding cortisol