Based on medical knowledge, we can create hundreds and thousands of justifications for which type of diet is healthier, why it is healthier and how much healthier it is. But medical science cannot decide which of the hundreds and thousands of medically substantiated claims is correct.However, if we take the results and evaluate them by mathematical-statistical methods, then the result is single and unambiguous. Yet none, at least a bit of a critical mathematician, would say: mathematical science recommends this and that diet, mathematicians recommend that diet. Life expectancy depends on two main factors, infectious diseases and civilization diseases. Where infectious diseases cause large-scale deaths, life expectancy is very low.