Lemme explain why that's impossible.
The stuff we eat can be broadly divided up into three big molecular categories: carbohydrates, proteins and fats. I call these "molecular categories" because we're talking about classes of molecules here. We're talking chemistry.
Each one of these molecules is essentially built up out of smaller component parts. Carbohydrates are made of saccharides, proteins are made of amino acids, and fats are made of aliphatics with a soupçon of glycerol.
Great! you might be thinking. Anything that's made of smaller, simpler parts should be something that can be synthesized, right?
Well … kinda.
It's true that the carbohydrates we eat are synthesized from saccharides, and the proteins are synthesized from amino acids, and the fats are synthesized from aliphatics. But it's how they're synthesized that makes them special: They're biosynthesized.
It turns out that the only practical way to turn saccharides into carbohydrates on any kind of useful scale is with a plant. A potato does a great job of it; a stalk of rice or corn is pretty good too if you're willing to do a little extra work. In fact there are a vast variety of plants that can biosynthesize edible carbohydrates out of nothing but air and water — heck, they're even solar powered!
To do that kind of synthesis in a lab would be astonishingly complex and hugely inefficient. We're not talking about baking-soda-and-vinegar chemistry here. We're talking about sequences of reactions thousands or tens of thousands of steps long that have to be carried out in exactly the right order with exactly the right reagents and most of them have to be catalyzed in some way because otherwise they're thermodynamically impossible.
But okay, let's set all that aside for a minute and play what-if. What if we had nanotechnology? What if we had nanotechnology so good it was basically magic? What if we used that magical nanotechnology to build a machine that could synthesize carbohydrates out of raw materials?
Then we'd just be reinventing the potato.
The same thing is true of proteins and fats, only more so. There's a good reason our body needs a diet composed mostly of carbohydrates; carbohydrates are abundant in nature! Proteins and fats are available in nature, but they're harder to come by because they're much harder to biosynthesize. Not to say there aren't some pretty amazing nanotechnological miracles that do it amazingly well, though. We call them cows. And pigs and chickens and tuna and so on. Animals biosynthesize proteins out of amino acids, most of which they also biosynthesize except for a few which they have to get from their environment. Protein biosynthesis makes carbohydrate synthesis look like folding a paper airplane. You just have no idea how complicated protein biosynthesis is, but trust me, it's a whopper.
So it's the same basic deal as before: If it were possible to build a machine that could synthesize proteins and fats, that machine would be a cow in all but name. And we've already got cows.
Okay, fine, so instead of synthesizing these bio-molecules that we need to eat out of their constituent parts — too impossibly difficult to do industrially — what if instead we just stockpiled the bio-molecules themselves and … I dunno … injection-molded a steak or something, instead of having to buy one from a butcher? Like there's a machine that has a bunch of slots in it for little bottles of raw food material and you just keep the bottles full and you can have anything you want?
Sure, let's go with that. And just to make it easy, let's stick to the steak idea. And to get started with, let's only consider the protein phase of a steak — that is to say, only the protein molecules that make up a steak, none of the other stuff. Know how many distinct proteins there are in a steak?
About a hundred thousand. That we know about. Remember, these things are molecules. We can't see 'em. We can only infer their existence through organic chemistry. So what we know is that your typical hunk of mammal muscle tissue contains at least 100,000 distinct proteins. The actual number could be ten or a hundred times that for all we know.
That machine you're imagining would need an absolute minimum of 100,000 different reagent bottles. And that's just for the protein phase of a piece of meat. We haven't started talking about fats or carbs yet.
Oh yeah. Did I mention vitamins and minerals?
Long story — well, still pretty long I guess, what you're imagining is simply not possible, not even in your wildest daydream. We're basically miraculous organic nano-machines ourselves, and we need to eat other miraculous organic nano-machines to live. Not even talking about being healthy or happy now; just to stay alive we need to rely on essentially the entire biosphere around us to biosynthesize the unimaginably vast array of molecules we need just to get through the day.