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From Carnivore to Herbivore
smooth wombat wrote in to mention an a recent discovery in the field of evolutionary biology. From the article: "A surprising discovery in Utah has paleontologists scratching their heads and asking: Why would a carnivore evolve a herbivorous diet? The species, christened Falcarius utahensis, belongs to a dinosaur group called the therizinosauroids. These are mostly thought to have been plant eaters. But the recently discovered fossil, the most primitive therizinosauroid found so far, seems to have survived on a mixed diet of meat and vegtables...The switch to vegetarianism is surprising, says Paul Barrett, who studies dinosaurs at the Natural History Museum in London. The therizinosauroids belong to a larger group of dinosaurs known as theropods, and many of these are known to have been excellent at catching a meaty meal. "
>>As you go up the food chain, you get less energy >>from the meat.
There are a couple of other trade-offs involved that make it less simple. "Pure" energy is converted less efficiently into meat, yes. But digesting meat as opposed to vegetables can be easier (less celulose) and allow simplification of digestive structures (drop the appendix, ditto multiple stomachs). Meat converts more efficiently into energy. Herbivores have to eat in bulk and spend most of their time foraging or digesting. Carnivores can go longer without food. But they have to hunt the stuff down.
I don't think this is confusing either - the balance can tip either way based on circumstances.
>alleviate the deficiencies in Vitamins B12 and D
Vitamin D is a hormone you synthesize in your skin from exposure to ultraviolet light (usually from the Sun). You might be interested to know that Vitamin D is ADDED to milk as a supplement.
B12 is from bacteria in soil. Historically it was also present in running water as it erodes soil. Modern agriculture depletes topsoil and consumers over-clean produce; historically you would eat a little dirt and thus get the B12, which has an RDA in MICROgrams.
Staying indoors and avoiding dirt are both side-effects of modern living, but evolutionarily, there is no reason being a plant-eating human would cause a deficit of these nutrients.
Modern life makes up for shortcomings with a pill. So, take your pick.