Vitamins are plentiful if you eat the right parts of the animal – most are stored in either the liver or fat. You just have to go straight for the organ meats, instead of throwing them out like we do. Muscle has lots of protein, and is more palatable to the modern tongue, but otherwise isn’t as nutritious as the rest of the animal.
And I think that humans can survive without fiber.
Cuz I was curious, I found this article from Discover magazine which answers your question in a lot of depth.
Short answer: Vitamins A and D are plentiful in the fats and organ meats. Vitamin C isn’t plentiful by our standards, but you can get enough. Something like one eighth of our “recommended daily allowance” of vitamin C is enough to ward off scurvy.
And eating nothing but protein can lead to toxicity, so the Inuit have to get most of their calories from fat.
Well, for starters, modern corn-fed beef have higher levels of omega-6 fatty acids, are thought to play a role in inflammation. Animals fed on grass (and by extension I’d presume wild diets) don’t exhibit this.
From the cite by lazybratsche:
"*A key difference in the typical Nunavik Inuit’s diet is that more than 50 percent of the calories in Inuit native foods come from fats. Much more important, the fats come from wild animals…
Wild-animal fats are different from both farm-animal fats and processed fats, says Dewailly. Farm animals, cooped up and stuffed with agricultural grains (carbohydrates) typically have lots of solid, highly saturated fat.
Wild animals that range freely and eat what nature intended, says Dewailly, have fat that is far more healthful. Less of their fat is saturated, and more of it is in the monounsaturated form (like olive oil). What’s more, cold-water fishes and sea mammals are particularly rich in polyunsaturated fats called n-3 fatty acids or omega-3 fatty acids. These fats appear to benefit the heart and vascular system. But the polyunsaturated fats in most Americans’ diets are the omega-6 fatty acids supplied by vegetable oils. By contrast, whale blubber consists of 70 percent monounsaturated fat and close to 30 percent omega-3s, says Dewailly"
Hunter-gatherers don’t eat meat, they eat animals. Lean muscle tissue is the least desirable part of an animal for them while fat, in the form of subcutaneous and organ fat, marrow, brain etc. is where it’s at. Eating just lean meat will quickly lead to severe diarrea and death (“rabbit starvation”). Fat dissipates protein toxicity, tastes better and contains more energy. Also, I can attest from personal experience that nothing boosts one’s morale in the cold winter woods more than a mouthful of hot animal fat.
Arctic plants have a much higher vitamin C content than their more southern relatives: a little goes a long way. Arctic sea mammals have appreciable vitamin C in their raw skin, as well.
In Western Alaska the natives got some berries from somewhere and beat them up with fat and made a candy bar like treat that was very popular with those who wanted to try the old traditional foods.
A curiosity that I have never seen explained, in the records found in transcription at the UAF library, the early European explorers reported scurvy worse in the late fall and early spring than it was in midwinter. I never found where anyone conjectured an explanation.
Early spring is exactly when I would expect scurvy to be worst. The body doesn’t store vitamin C, but it takes along time to deplete the stuff in circulation and for the symptoms of deficiency to be seen. So you would expect the symptoms to be worst at the end of a prolonged period without vegetable foods, which would logically be the end of winter and beginning of spring. Most of the common edible plants aren’t available until late spring or early summer at the earliest, so in early spring you would have had 6 months of so of no fresh vegetables available.
Late autumn is harder to explain. One would assume that by this stage an explorer living off the land would have been making the most of the berry harvest for several weeks at least, and other plant foods for several months.