Many of the benefits, such as weight loss, are experienced at lower levels of ketosis (above 0.5 mmol/L). Although getting sufficient protein on any diet is important for preventing muscle loss, many questions have been raised about protein’s impact on ketone levels. So unless insulin is given via injection or IV, ketones will continue rising to life-threatening levels. Ketosis does not usually occur in people who eat balanced diets and regular meals.
FGF21 therefore mediates a unique physiological niche, coordinating adaptive shifts in macronutrient preference which serve to maintain protein intake in the face of dietary protein restriction. Achieving ketosis can be difficult for vegans and vegetarians, as many keto favorites like eggs or dairy are not an option. For those that follow a meat-free diet it’s best to rely on high-fat, plant-based sources of healthy fats like coconut oil, avocados, seeds, nuts and vegan meat replacements like tempeh and tofu.
Long story short — from an evolutionary perspective, we evolved the ability to burn ketones for fuel as a means to preserve muscle mass and fuel the brain during times of food scarcity. Without ketosis, the body would be forced to use gluconeogenesis to fuel the brain exclusively, burning through muscle mass until we could not function any longer.