Can a human exist on a diet of protein alone

…and if not how do the carnivores manage it, for example crocs, lions etc.

Meat contains many other things besides protein. Some animals, e.g., cats, can also synthesize vitamin C and so don’t need to get much in their diet. Humans can’t do this, though.

One thing is they eat the entire animal, or at least major parts, not just the flesh like most humans.

What Telemark said. The stomach and it’s contents is often a favored (and fought over) part of the omnivore/herbivore they are consuming.

Another thing not yet mentioned is that protein can be burned for “fuel” just as carbohydrates can. In fact, both proteins and carbohydrates are worth about 4 (kilo)calories per gram, IIRC.

So a human carnivore would be broadly OK from an energy standpoint. I know that complex carbs are suited for sustained, steadily-released energy and do not disturb the body’s insulin levels so much. Simle carbs do the opposite – provide quick bursts of energy and cause a rise-and-crash in the blood insulin level. I don’t know how the body’s insulin level would respond to an all-protein diet, though.

Adopting all-protein diet would seem to tempt some forms of vitamin deficiency. Also, aren’t their some risks of kidney failure from low-carb and no-carb diets?

I believe that certain Eskimo’s closer to the Arctic Circle eat diets that are nearly 100% carniverous. This is because edible plants don’t grow as well there. Also, the meat that they eat is very rare which keeps more vitamins in.

From here.

Also there is a Straight Dope Column on the subject.

Here is a quote from said article:

A few holdouts didn’t buy it. To settle the matter once and for all, Stefansson and a colleague lived on a meat-only diet for one year under medical supervision at New York’s Bellevue Hospital, starting in February 1928. The two ate between 100 and 140 grams of protein a day, the balance of their calories coming from fat, yet they remained scurvy free. Later in life Stefansson became a strong advocate of a high-meat diet even if you didn’t live in the arctic; he professed to enjoy improved health, reduced weight, etc, from meals consisting of coffee, the occasional grapefruit, and a nice steak, presumably rare. Doesn’t sound half bad, and one might note that until recently the Inuit rarely suffered from atherosclerosis and other Western ailments.

I first heard about this through a documentary on PBS. I wish I could remember the name.

If you burn them. The caloric requirements to digest protein are a bit higher than those for digesting carbs. I want to say that once you take that into account, carbs still have about 4, protein 3, and fat about 8.5.


Right now, there’s no evidence that a high-protein diet causes kidney problems for people who didn’t have kidney problems to begin with. However, people who do have kidney problems are advised to stay away from high-protein diets.

An all meat diet can be survived on- but fiber would be a problem. An all protein diet- no. Meat has plenty of vitamins. Pure protein has none, of course. Nor could one survive on pure carbos.

Meat has fat in it as well. You need fat or you will die. So the answer to the original question is no you cannot survive on just protein, cos you need fat. Eskimos eat a lot of fat because in cold climates you need to eat more fat than in hotter climates. Fat contains more energy than carbs or protein(which has least).

When people go on expiditions to the south and north pole they take high fat foods with them like chocolate. One reason the first explorers died trying to get to the south pole was they took high protein foods - big mistake cos they are low in energy.

High protein intake can cause loss of calcium, so you may acquire some calcium deficiency problems, such as osteopenia/osteoporosis, nerve conduction, etc.

Barbitu8- yes, but meat has more than enough calcium to cover that. Well, maybe not a womans long term needs, since they need extra.

Semi-hijack - what percentage of a typical lean meat such as a chicken breast is protein? Like, how many actual grams of protein would I get from eating one kilo of it? I was just wondering about that one day. How about for other common meats such as beef or pork? Anyone know?

To add to what The Griffin said, you need fat in your diet because the vitamins A, D, E and K are fat soluble and if you eat no fat, you get none of these vitamns, all of which are essential.

DORKUSetcetera: I understand that the Eskimo also eat lichen from rocks and also some kinds of edible seaweeds.

Protein alone, no. The body can convert protein to glucose to burn as fuel, but only within limits. According to fat researcher–I should say “researcher on fat”–Caroline Pond, one can get only about half of one’s calorie requirements from protein alone. Trying to live on a high-protein, low-fat, low-carbohydrate diet leads to a condition called “rabbit starvation.” You need to get about half your calories from fat or carbohydrate or a combination. No matter how much rabbit muscle meat you eat, you will eventually waste away if you eat nothing else. You just can’t use enough of it for fuel. If you leave some of the muscle meat and eat all the fattier parts of the animal (marrow, brain, etc.), you should be able to avoid rabbit starvation.

In addition to the calorie problem, you need small amounts of essential fatty acids. Ordinary body fat of land animals is a very poor source of essential fatty acids, but fish oils and blubber of marine animals and brains and eyeballs of land animals are pretty good sources.

Mmmm, Brains! Now you’re talking. Oooh, Oooh, and eyeballs as well, yummy!!

you would not survive on pure protein. you would also need essential fatty acids, vitamins and minerals.

the amount of essential fatty acids in meat depends on what the livestock was fed. grass fed livestock has best EFA profile, but most livestock is grain-fed.

there is a different reason for not eating rabbit alone. They lack a certain amino acid that humans need if my memory serves me correctly, and you WILL die if the only protein you get is rabbit protein.

Again just chiming in that fat is esential to good health and if taken to extreme, life itself. Zero carb is another story as your body can convert protein to carbs to supply all the carbs nessesary, which is for the brain only IIRC (AFAIK glucose is the only energy source that can pass the brain-blood barrier).

So carbs are the only macronutrient that may not be essential for human life.

Also another factor that should be considered is that if one is not consuming carbs at all, they will need a steady amount of protien to convert to glucose. If they are not taking in protein steadly (i.e. 3 meals/day), then the body must get the protien from somewhere, and starts breaking down itself.

Technically protein can be converted to carbs AND carbs can be converted to fat, but in a zero carb diet the amount of protein converted will be minimal, and for any reason there are extra carbs they will be stored as gyclogen which will later be used as glucose, as glycogen stores will be depleted and muscles will be running on fat alone.

**** Note all the above is a NON-professional viewpoint from a ong time low carb’er.

Do you have a cite for the protein conversion to carbs? AFAIK, this is not so. True, the body can use protein for energy, but it does so w/o converting it to glucose.