I was looking at some data with respect to meat only diets and the risk of developing Vitamin C deficiency. While these and other concerns are very real and need to be taken carefully into consideration if one decides to follow such a diet, unless one consumes lean meat only, chances of developing scurvy are not increased.
Scurvy is a life-threatening condition that appears on the background consuming less 10mg of vitamin C per day for several weeks. If this was the only problem of carnivore diets...
Okay, so, such a diet is also known as a zero carbohydrate diet and it can include eggs and other animal products with little to no carbohydrates. Technically, it's not zero because meat can contain glycogen and eggs have 0.3-0.5g of carbohydrates per egg. But for all intents and purposes this diet is very close to zero carbohydrates.
So, if one consumes liver and other organ meats, these are very nutrient rich (in fact, liver is one of the most nutrient rich foods), it contains vitamin C. For reference, 100g of liver contains about 28-30 mg of vitamin C. On top of that, vitamin C competes with glucose for absorption (see GLUT1 receptor) and on a background of little to no carbohydrate intake, more of Vitamin C would be absorbed.
Those on a carnivore diet could always take a vitamin C pill and forget about all this. However, there might be more implications to the diet, some positive, some less...
As a parallel, a ketogenic diet is still restrictive, but much more varied than a zero carb diet and it can include several servings of vegetables and some low-glycemic fruits which can meet most of the requirements for vitamins, minerals and micronutrients if formulated appropiately. But, this is not about the ketogenic diet...
A very long post about the carnivore diet was written by Sean Hyson at Onnit. I found it an interesting read and I'd suggest reading it if you find this subject appealing:
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Cristi Vlad Self-Experimenter and Author