Laboratory animals on a chemically defined diet. No real food.
There are thousands of “non-essential” nutrients in an animal’s body and there are thousands of locations throughout the body in which those nutrients do things.
It is impossible for any animal to have all of the millions of these parameters at the optimum levels.
Some nutrients are deficient in some places and other nutrients are in excess in other places.
Deficiency is by far the more common in lab animals fed a chemically defined diet.
Any deficiency becomes a conditionally essential nutrient that must be obtained from the diet or from supplements. Laboratory animals have a lot of these.
Consequently, when science makes a discovery in one lab animal and confirms it in another lab animal, unfortunately, the same artifact-producing problem is being repeated with a different laboratory chow. No real food, which alone can supply thousands of materials, any group of which can be deficient at some locals within the body.
Is calorie restriction’s increase in the max achievable lifespan of various laboratory animals an artifact of chemically defined diets? Perhaps – but the benefits of some type of fasting, particularly in the allowance of a proper amount of autophagy, are probably real.