How is it that we, as humans, are constantly fussing over having a balanced diet with the right proportions of carbohydrate, protein, vitamins, minerals, essential oils etc. while other mammals apparently don’t need to bother? I understand that as omnivores we might need a broader range, by nature, than a strict carnivore/herbivore, but aren’t pigs omnivores? Do they obey the nutritional ‘pyramid’ of balanced diets?
Or consider the cow. It spends all day eating grass which is broken down by its lengthy digestive process, but how can there be every necessary element to create a cow from grass alone (and maybe an occasional salt-lick)?
Are animals routinely malnutritioned? Do lions get scurvy from the lack of citrus fruit on the savannah? Do squirrels go infertile from not enough zinc (or whatever…)?
The answer’s probably obvious, but I need to know, or I’ll be haunted by visions of malnourished gibbons, badgers, fieldmice…
'Cause they’re cows. They evolved to eat grass. Their digestive system has mechanical and chemical means to break down plant matter to extract all the nutrient they need from that. Ours didn’t. But don’t think they can’t eat meat protein - they can, and domesticated cattle do, and digest it quite well. They don’t have the teeth or claws to get it for themselves, though.
Or, to look at the other side of it, any cows or proto-cow creatures who couldn’t survive off grass died before they could have more flesh-needing cow babies. So all that’s left are the grass eating cows.
Why do we need to balance our diets? 'Cause we don’t live a natural life, the ways cows can. If you’re wandering in the woods or even on the plain, most of what you have around to eat is vegetation - those leafy greens and other vegetables everyone tells you to eat more of. Sometimes you come across a meat source. There are scant ice-cream bushes in the jungle, however.
Mess with the food sources we evolved to eat best, and you invite all sorts of trouble: obesity, heart disease, cancers. So we spend a lot of time trying to intellectualize what, in nature, we’d be doing simply due to availability.
We certainly evolved to tolerate a wise range of diets, from the almost pure carnivore diet of the Inuit to the vegan diet to the McDonald’s diet. Are they all equally good for us? No. Can we live on all of them, for a while at least? Yes. Again, any baby born to Inuit people who couldn’t tolerate meat would die before giving birth to more meat-intollerant Inuit. Our amazing ability to digest such a wide range of foods is what allowed us to live all over the world in such varied climates as to be almost ridiculous.
It’s probably worth noting that even the strictest of “carnivores” does eat some vegetable matter - in the undigested food in the stomachs and intestines of its prey. And even the most well-meaning Buddhist vegan eats some animal protein - in the form of bugs that fall or crawl into grains before or during cooking. These small amounts of a “varied diet” provide these extremes with the required nutrients that they don’t think they’re getting.
Maybe the cow example was a bad idea - as a domesticated animal, Og only knows what they’re fed (BSE, anyone?).
But how about the scurvy issue then? How do the big cats get their RDA of Vitamin C? Or, as they are no doubt ‘evolved to eat meat’, do they not need the vitamins that an omnivore might?
Absolutely. To some extent I suppose we are striving against the march of civilisation to get back to a more ‘natural’ range of foods.
Could the leafy/grainy stomach contents of carnivores’ herbivorous prey give them all plant matter they require then?
No, I think the cow example was a good one. The fact is, with processing, most animals, including humans, can eat all sorts of things they wouldn’t normally. You have to catch, kill and grind up meat before you can feed it to a cow, because it doesn’t have the drive or means to hunt or the teeth to rip meat of bones. But process it in a way that it can get it into it’s mouth, and it can digest it. Same with humans. We’re not “meant” to eat coffee beans, but process them in water and throw out the bean itself, and we can “eat” coffee! Dogs can’t naturally eat a lot of corn, but it’s the primary ingredient in most dog foods. Whether it’s good to tamper with the natural diet is a matter of debate (and great debate in some circles!) but the fact is clear that they can live on the stuff.
In a natural setting, there’s no doubt that cows eat only vegetation (whether or not it’s all “grass,” I’m not sure. I think too much grass makes 'em bloat and they need grain, but the point is still the same.)
Let’s wait for **Colibri **to wake up; he can explain it better. But my basic understanding is yes, the “RDA” for Vitamin C in a big cat is small, and is met by his mostly carnivorous diet, probably by the plant matter he eats in viscera, but his body may also have ways of processing and using the Vitamin C in the flesh of his prey.
There’s sort of a trade-off in dietary evolution. Either you can naturally eat and digest a small range of foods really, really efficiently (strict herbivores and carnivores) or you can eat and digest a rather large range of foods less efficiently (omnivores). Since omnivores digest less thoroughly but with wider range, we need a wider range of stuff to eat in an optimal situation. (And which came first is a chicken-an-egg question.) But, again, that flexibility lets us get away with shockingly “bad” diets for a long time before we die of malnutrition or diet-induced illness.
Damnit I spend my life in a state of shock at what I don’t know.
Is that similar to the production of Vitamin D in sunlight? Vitamins clearly can’t be made from sunlight, so does perhaps the sun’s energy stimulates us to turn glucose into Vitamin D? (I’m pushing it here with my shaky parallels of course…) Is this synthesis of vitamins quite widespread in the animal kingdom?
“Vitamins” are not a chemical group; they are not related to each other by chemical structure the way that amino acids are. The are lumped together by nutritional criteria, not chemical.
The precursors for Vitamin D are different from the precursors for Vitamin C. Vitamin D is produced from fat in your skin, but in the temperate zones you are not likely to be getting enough sunlight to produce the required amount.
IIRC, only the Great Apes and guinea pigs have lost the ability to synthesize ascorbic acid (Vitamin C), so only those few species need to replace it through diet.
Correct. Each species has its peculiarities as far as nutrition. Cats must have taurine in their diet or else they will suffer from blindness and cardiac disease. Many other species can synthesise taurine from its components.
Cows have a complex upper GI tract that allows them to process vegetation.
They repeatedly regurgitate and re-chew the material, ferment it, expose it to microbes, all to get the energy present in it.
I’m going to give my cat a bowl of Red Bull from now on. :dubious:
No speculation as to what evolutionary hiccup lost the apes and guinea pigs that Ascorbic acid manufacturing ability, I suppose? Seems a bit counter-productive…Either way, this is great stuff to learn, cheers!
My WAG is that it was a result of a diet high in leafy greens and/or fruit. They got enough Ascorbic acid in their diet, so didn’t need to hold onto the ability to make it from scratch anymore.
For full-time carnivores, keep in mind that they eat the whole animal (excepting bones, although they do often chew on them) and get all sorts of nutrients that way. They end up getting whatever their prey animals have in their bodies.
Actually, all commercial cat foods have adequate taurine. In the 80s, when the cat’s need for taurine was first discovered, most cat foods had adequate amounts. Some generic foods were deficient, however. The only taurine related disease I see nowadays is in cats fed strange diets, like the cat I saw last month that was fed dog food. The owner figured cats were sorta like small dogs, and he was already buying dog food, so what the heck.
Excuse me for gloating, but there’s been a longstanding argument over a cat in our family who went blind after eating nothing but dogfood for most of his kitty-life. The rest of the family thinks there’s no connection.
Poor Alex-kitty: blind, deaf, declawed in all 4 (I was a kid, I had no say!), and the dog chewed off all his whiskers for a hobby. How that kitty managed to be the best mouser I’ve ever owned, I’ll never know! [/hijack]
However, raw meat, especially organ meats, contains vitamin C, and this is apparently how Inuit and other northern peoples managed to get by without eating much plant material. The master on the subject: Traditionally Eskimos ate only meat and fish. Why didn’t they get scurvy?
As to why some substances are vitamins for some animals and not others: when a substance is pretty much guaranteed to be present in the normal diet, evolution will sometimes dispense with the physiological machinery for manufacturing it. This is just a matter of efficiency: synthesizing complex organic compounds is often energetically costly, so why bother if you always get it in your diet anyway?
Apes, and humans under the conditions in which they evolved, ate lots of fruit and other sources of vitamin C, so there wasn’t much need to manufacture it. Cats, on the other hand, live on a diet that is rich in taurine, so they dispensed with that particular compound, which is a vitamin for them but not for us.
Human vitamin deficiencies in any case are almost exclusively due to a highly non-“normal” diet, or else to living in an environment very unlike the one in which we evolved. Scurvy only normally appeared in those on long sea voyages who ate no fresh vegetables and only preserved meats. Vitamin B deficiencies were discovered when people developed problems from living mainly on highly-polished rice from which the vitamin-containing part had been removed by processing. Vitamin D deficiency develops in northern areas where there is insufficient light in winter months to manufacture it in the skin. And so on.
Most humans eating a “natural” diet that includes fruit, green vegetables, grains, and a little meat will get all the vitamins they need. “Unbalanced diets” and vitamin deficiencies are largely a product of civilization.
Cows eat grass, but they have microbes living in their stomachs that actually process and digest the grass. The microbes multiply in the cow’s stomach at the fast rates typical of bacteria, so that there are enough microbes to process whatever the cow takes in. The cow itself then digests the microbes after they have done their work, along with whatever plant resudur may remain. So, in effect, the cow is actually eating a balanced diet of meat (microbes) and plants. See this site for more info.
Animals like rabbits don’t have the nifty 4-chambered stomach to eat grass as efficiently as ruminants (which is what cows, along with deer and many other big herbivores, but not horses) can. Rabbits do have a greatly enlarged cecum (in humans it’s our appendix) that help them ferment cellulose, but they also eat their droppings to reprocess stuff that was only partially digested the first time around (read more here). Koalas are another animal with a very large cecum.
I have heard that some of the nutrients carnivores need come from the stomach and intestinal contents of their herbivorous prey.
I’m glad you started this thread. I keep running into people who see all animals as little humans, or as identical to other animals in their phylogenic group, and try to feed and house them accordingly. It takes a while to convince someone that no, their dog can’t have ibuprofen, their cat can’t be doused in eucalyptus oil, their parrot can’t have avocados, and their green iguana can’t live with their leopard geckos. Research, people!
</rant>
Anyway, you’d probably really like a comparative biology course at your local college. Sometimes the professor will let you sit in for s&g if you ask nice. Neat stuff.
easy e, not to mention that the horse is another animal with a very large cecum, along with a very big large intestine (or descending colon: right ventral, left ventral, left dorsal, left ventral, with the pelvic and diaphragmatic flexures).
Think of vitamins as “vital amines”. Although not all of them are amines or derived from amino acids, these are chemical compounds that are important (vital) in many metabolic process that occur in your body. Without them you cannot create other compounds (vitamin A, for example), or synthesize other materials (like collagen), or prevent the damage of other chemicals (that’s part of what vitamin E prevents). They’re also used as co-enzymes, and help reactions occur faster than they would (and at the rate they’re needed).
Vitamin D is not a relative of vitamin C, they’re not even in the same classification of vitamins. D is fat-soluble while C is water-soluble. And I forgot what the precursor of D was, but I’m thinking maybe a sterol.
And yes, there are other vitamins that animals can synthesize, like vitamin K. Under normal conditions, you don’t need vitamin K (involved in coagulation). It only becomes a concern when there has been some type of poisoning.
If the animal can get enough of its vitamin requirements from its diet, there’s no reason why it should keep wasting energy synthesizing that compound. That energy could be put to better use.
Plants, like animals, need many of the vitamins we need for either similar or different reasons.
I suspected as much. I just clearly remember the rabbit and koala examples from my physiology classes.
Cholesterol is the precursor to D3 and ergosterol the precursor to D2. UV light is needed to start the synthesis process (ergosterol->viosterol). I studied biochem at Wisconsin, where Steenbock figured out you could fortify foods by exposing them to UV light, creating viosterol, so you can imagine that whenever we got to vitamin D in biology, organic chemistry, or biochem we heard all about it. We heard a lot about the development of warfarin (aka coumadin), too.
