enormous even
Pleonast: Interesting, but not really practical. Synthesizing all those proteins and amino acids would consume a lot of energy and resources. You’d have to compensate for this, probably by eating large amounts of carbohydrates. As omnivores, it’s more efficient for humans to let other organisms synthesize vitamins and the more difficult-to-produce amino acids for us. That’s why we don’t have the ability to biosynthesize them in the first place – we don’t need to. Same for photosynthesis, or digesting cellulose.
That being said, there are already products available that contain large amounts of ‘complete’ protein; they’re often made from whey and used in bodybuilding. However, they probably taste awful and are expensive – far more expensive than most natural high-protein foods.
It might be possible to create overproducing strains of E. coli for each essential amino acid and vitamin, then gather the products and package them together. (Or maybe you could just ‘infect’ people with colonies of all the overproducers.) Even so, like I said, your carbohydrate requirements would increase drastically. You might end up contributing so much carbohydrates to your bacterial colonies that you get malnutrition anyway… Also, since biosynthesis of exotic organic compounds very often requires metal cofactors, you might need to consume large amounts of, say, nickel or molybdenum to keep the colonies working. (Metal salts are plentiful, though, so you could take them in tablet form.)
As for the first question, I’m not really sure. A few things to consider, though:
- The limiting amino acid in wheat (semolina is made from wheat, right?) is lysine. I can’t seem to find whether insects can biosynthesize lysine (my intuition says they can’t), but, if they can, then that removes a major obstacle in their growth. It’s also possible you could have a co-infestation with a mold or fungus that produces some lysine.
- The package is a closed system, as you said. So, when the insects die, they leave behind a cache of amino acids for the rest of the population.
- The package contained a lot of food, from an insect’s perspective. So it would be some time before they depleted the available resouces. Also, even though wheat is lysine-deficient if a human bases their diet on it, insects probably can get enough of all the amino acids – there’s some lysine in there, just not much.
When all the semolina was depleted, the insects would begin to use proteins (stored and otherwise) as their primary energy source. This is relatively inefficient compared to carbohydrates, but you have to synthesize ATP somehow. =) The byproducts of amino acid catabolism are CO[sub]2[/sub], water, and some kind of nitrogenous compound (urea, uric acid, etc. – I forget which one arthropods use). So, ultimately the protein content would go down.
One more thing. Mnemosyne, maybe I’m misunderstanding, but I think you’ve got the ruminants a bit out of place. I don’t think carnivores lost the ability to digest grasses; I think ruminants gained it, and became a specialized group of mammals. Otherwise you’d expect humans (and cheetahs and wolves) to have vestigial stomachs. =)
Re: ruminants gaining the ability to eat grass
Yes, that makes much more sense. I was thinking in a very generalised way about gaining/losing evolutionary abilities - it didn’t occur to me to think in that much detail about it! I think I was just going along with the idea of something ate plants, now two creatures exist where one can and the other can’t - they diverged a long time ago, and this is a difference. Can I amend my statements?
Silly me. 
It’s Bio Geek-Out Time. Allow me to muddy up the discussion a bit.
The most common protein on Earth is ribulose bisphosphate carboxylase/oxygenase, AKA ‘rubisco’ (pretty picture: www.rcsb.org/pdb/molecules/pdb11_1.html). It’s the ‘fossil enzyme’ that fixes carbon and makes most (macroscopic) life on earth possible.
Plant materials in general are low in protein (compared to, say, animal tissue: mostly protein). Seeds and grains usually have more amino acids than other plant materials, but they are often in weird ratios or contain lots of one or two aminos that animals have little use for unless they are broken all the way down and resynthesized.
Most animals are much more competent at making amino acids/vitamins than humans. The weevils (c/b Tribolium spp.) you find in your spoiled oatmeal are not adding any nitrogen/amino acids/proteins, just converting them into potentially more useful forms for humans (to address the OP question). That’s why Tribolium weevils are notorious for cannibalism.
That said, don’t eat the oatmeal. Tribolium spp. “know” (sorry, can’t help anthropomorphosizing evolution sometime) the grain they infest would be a “value added” product, so many are poisonous (http://www.fao.org/inpho/compend/text/ch02-01.htm).
I have never heard of humans gaining extra nutrition from food infested with invert.s or larger organisms; though it is a common phenomenon with microbes like yeast “spoiling” bread, beer, etc., molds making cheese… (tiresome list follows). I have heard of elephants, pigs, and other large mammals enjoying slighly spoiled crops of fruit due to their possibly increased nutritional value…
I’d just like to express my gratitude to everyone who has contributed to this thread, it has been very interesting and informative.
Oh, I am probably only perpetuating an urban myth, although I did find this story
The first few days out I saw them throw the biscuits in the garbage. The next few days they merely picked out the weevil and ate the biscuit. It wasn’t long until they just wouldn’t look and considered the weevil an extra protein and chomp away. (Marines are tough you know.)
and
here- (pdf)
And in the morning, kind of an oatmeal-barley type of soup occasionally with, you know, they were really laced with weevils, but at the very – at the first – first look, why you kind of turned up your nose but then you realized that, no what the heck, this is another source of protein so, you know, they just become part of the normal diet.
Perhaps they became immune/tolerant of the toxins produced by the weevils?
Or perhaps these stories are badly remembered/ idealised?
One oe two possibilities there.
It would certainly be true that removing the weevils would reduce the overall protein content, even if they had not increased it above the original value.