huh? I mean, we already have foods that last longer and are healthier than things in the past, because of science (both genetics and chemical sciences, as well as, well, refrigeration.) Why is it such a leap to think that in the future we can have foods that last longer and are healthier? Maybe a salt that doesn't get absorbed into our body, so it prevents microbes from taking on our food, still tastes the same, but doesn't give us more sodium than we need/can handle?
Because what you're proposing
doesn't make sense. You're suggesting no mechanism for it 'lasting longer' other than 'SCIENCE', and the idea of something tasting like Sodium Chloride whilst not, in fact, being NaCl doesn't mean it's going to be better for us. It's not the only salt that the body uses (I think Magnesium Chloride is used for nerve connections as well?), and just putting random metal/nonmetal combinations into food probably won't do too much for our health other than poison us.
Specifically, I referred to the chemical one--that's no an option for improving healthiness, since you're just changing whether it's there from the start or you put it on later--and I can't think of many genetic modifications that are going to prevent, say, vegetables from going soft and mouldy. Changing the structure or composition to do that is going to mess with
some desirable quality--texture, taste, how it digests (from messing with the structure), nutritional content...
And I will give you that it's impractical to engineer the genetics of coming generations....for now. But eventually, we will be using genetic engineering to remove genetic disorders and diseases, and make people better overall. Why would how we deal with our environment be any different from those? We've already engineered foodstuffs to be more nutritious and more abundant, why can't we eventually make us work better with the food? And to be clear, getting rid of that reflex would make us eat less, not let us deal with eating more. That's the lazy solution, and the harder one. The good solution is to engineer us to make us eat more appropriate levels of food.
Because it's blindly optimistic. Because genetically engineering billions of people's unborn offspring requires the sort of achievements where 'eating healthy' isn't really a concern, since you apparently assume that some force is available to do this to all of humanity. Or are you proposing creating a class divide bigger than anything the world's ever seen so far? That's not good, either.
And, of course, there's no positive reason to try and optimise something as complicated as the human genome and all the resulting protein interactions: it's going to break. Conditions will change away from that which supported the initial alterations, and you'll have gutted the human body of the 'superfluous' stuff that
actually deals with adversity.
For those alterations to even begin to be practical, you need political unification, actual or effective; to remove the risk of possibly starving to death, since you've taken away all mechanisms for dealing with times of scarcity; and a level of scientific knowledge that is essentially 'solved the workings of the human mind, everything about protein folding, the role of every protein and chemical in the human body, and how to intricately control one system without breaking the other myriad interconnected systems.
At which point, I'd really hope anyone trying to do that would be dragged out into the street and tossed in front of a moving vehicle, because it's pretty much a sci-fi dictatorship by that point.