I watched a german TV news item on why people put on weight and the researcher there was pushing the idea that it is a survival advantage. He was claiming that people are programmed to recognise fat and sugar as two sources of energy in foods and to take advantage of it whenever they encountered it. Of course, in those hunter gather days, many didn't know where the next meal would come from. Those who could convert foods to fat easily stood a better chance of making it through to the next meal. An alternative strategy would be to conserve energy, but this became increasingly disadvantageous as human groups competed for resources. He mentioned the tendency amongst some people to eat very quickly or to keep looking around whilst they do eat, on the lookout for someone who may steal the meal. Of course, those who can eat and store fat easily thesedays, just become overweight, but the genetic programming is still there, 'take advantage of this meal.'
The particular researcher concerned was not approaching it from a medical point of view but from a nutrition point of view. Too many ready meal manufacturers pack their foods with either sugar or fat or sometimes, both.