It’s not a question of the number of calories–clearly there’s a positive energy budget in even the leanest meats–but a lack of the nutrients that are an inherent part of the Krebs Cycle, as can be seen from the diagram. Without them, the body has to scavenge both fatty acids and amino acids from tissue, which leads to starvation regardless of raw calorie input.
Nutrition is more than just blind calories. Mangetout has it right; humans (like pigs and bears) are evolved to eat a broad, omnivorous diet; dedicated carnivores have different secondary mechanisms that help them break down lean proteins, though they still require carbs and fats from some aspect of their diet; just not as much or as concentrated and accessible.
I think the article that slaphead linked to pretty much explaines the thing.
It says that in this case, the main problem is a lack of calories. Since the machinery in the liver is simply uncapable of using all the protein as fuel.
That is, if the claim is true.
To me their argument seems sound, if a bit sketchy. It doesnt seem like they expected this article to be scientifically reviewed. They don’t show their calculations, and they have some unclear statements:
"We have data about the total amount of oxygen supplied to the human liver. "
Is this data from patients on a strict protein diet? And if not, is it maybe plausible that the oxygen supply is increased in time of need?
"Four ATP molecules are used to convert two NH4+ to urea and six more are required to convert the carbon skeletons of these amino acids to glucose. "
The amount of ATP required to turn an amino acid into glucose would certainly depend on the type of amino acid. Maybe they are thinking of an average value. I wonder how they got that though.
Looking a bit around on the site slaphead linked to, I found this article. Not actually related to this threat, sorry, but its pretty interesting.
It says that:
-“The use of high-fructose corn syrup (HFCS) has increased markedly during the past 30 years.”
and
-“Fructose does not cause insulin release from beta cells, as these lack fructokinase. One of the results of this is that fructose consumption does not dampen appetite. This may lead to increased caloric intake with obesity and the metabolic syndrome as a result.”
In his book Never Cry Wolf, Farley Mowat observed wolves eating primarily lemmings and mice. He wasn’t sure if they were eating something unobserved by him, so he set out to do an experiment: to see if a large carnivore could get by on that diet, he set out to eat it himself. He noticed that he started craving fats, but then he realized that the wolves ate the animals whole, innards (which have a lot of fat around them) and all. Once he started cooking them whole, the craving went away.