"If the primary change in traditional diets with Westernization was the addition of sugar, flour and white rice, and this in turn occurred shortly before the appearance of chronic disease, then the most likely explanation was that those processed, refined carbohydrates were the cause of the disease. [...] This would explain why the same diseases appeared after Westernization in cultures that lived almost exclusively on animal products - the Inuit, the Masai, and Samburu nomads, Australian Aborigines, or Native Americans of the Great Plains - as well as in primarily agrarian cultures like the Hunza in the Himalayas or the Kikuyu in Kenya."
- Gary Taubes
The conventional wisdom says:
A varied diet is essential for good health.
A diet rich in meat and poor in plants is unhealthy and will lead to deficiencies.
These assumptions, still prevalent today, are based on studies of deficiency diseases. The problem is that deficiency diseases appeared in areas where the diet was high in refined carbohydrates and low in meat, fish, eggs.
A few examples of deficiency diseases:
Scurvy (vitamin C deficiency): On long sea voyages, it was important to prevent this condition. For example, in the middle of the 18th century, James Lind - British naval surgeon, added citrus juice to the sailors diet, composed of "water gruel sweetened with sugar in the morning, fresh mutton broth, light puddings, boiled biscuits with sugar, barley and raisins, rice and currants." Captain Cook prevented scurvy by "forcing" his crew to consume a small amount of sauerkraut every day, in addition the a diet of hard bread and salted meat.
Pellagra (vitamin B3 or niacin deficiency) was found in populations where the staple food was corn.
Beriberi (vitamin B1 or thiamine deficiency) is associated with a diet rich in polished rice rather than brown. Takaki Kanehiro, a British-trained Japanese medical doctor added meat and fish to the crewmen's original diet of almost exclusively white rice.
Where do we get the vitamins and minerals from?
Animal foods contain all of the essential amino acids necessary to build healthy body structures. Wheat is also rich in all essential amino acids, but we have to consume nearly 5 times more, to get the same amount of nutrients we get from meat. "Meat is a particularly concentrated source of vitamin A, E and the entire complex of B vitamins. Vitamins D and B12 are found only in animal products [...]." (Gary Taubes)
We can get all vitamins and minerals from animal foods and our capacity to absorb these nutrients is the highest when they are derived from animal products.
An example is vitamin A. This vitamin is found in high concentration in animal fat. Carotenoids are found plant foods, for example carrots, and leafy green vegetables. We have the ability to absorb and convert carotenoids to vitamin A, but I would call this conversion ratio ridiculously low. In one study the conversion ratio was roughly 0.05%. The absorption, on the other hand, from animal sources (liver, egg) is much higher, more than 50%.
It is interesting to note, only primates and guinea pigs are unable to manufacture vitamin C on their own, having lost the genetic information necessary to create this important dietary component. So, diet is the only way to supply our body with vitamin C. But how do we get our vitamin C if we do not consume, let's say oranges? And how did the Inuit, the Masai in Kenya and other populations get this nutrient if their diet was primarily animal food?
Citrus fruits, cabbage, broccoli... are a good source of vitamin C. Certain animal organ meats also contain this vitamin. The Inuit consumed the skin of a certain type of whale, which was very high in vitamin C. Native Americans found their vitamin C supply in organ meat.
"[...] The Indian kills a moose he opens it up and at the back of the moose just above the kidney there are what he described as two small balls in the fat. These he said the Indian would take and cut up into as many pieces as there were little and big Indians in the family and each one would eat his piece. They would eat also the walls of the second stomach. By eating these parts of the animal the Indians would keep free from scurvy, which is due to the lack of vitamin C. The Indians were getting vitamin C from the adrenal glands and organs. Modern science has very recently discovered that the adrenal glands are the richest sources of vitamin C in all animal or plant tissues."
- Weston Price
If these populations thrived eating a diet devoid of fruits and vegetables, it means that they were getting all the nutrients required for optimal health, no deficiencies have been observed in these populations. The amount of vitamin C consumed was lower than what we get on a high fruit and vegetable diet, but it seems that it was sufficient in order to thrive even in a harsh climate. I would like to emphasize here that refined carbohydrates and sugar were completely absent from their diet.
Now, about the biochemistry of vitamin C:
By the 1930s, nutritionist established that a diet high in carbohydrates depletes the body of the B vitamins. The same argument goes for vitamin C. Diabetics, for example, have 30% lower levels of this vitamin than normal people. We know that diabetics became diabetics because of their diet high in refined carbohydrates and sugar, which in turn causes high insulin levels. It is then a reasonable assumption that high level of insulin causes low levels of vitamin C.
High carbohydrates in the diet lead to low vitamin C levels.
This means, that if we eat a high carbohydrate diet, our requirement for vitamin C is higher and vice versa. If our diet is low in carbohydrates, even a small amount of vitamin C must be enough to thrive.
Why? Vitamin C has a very similar structure to glucose (blood sugar). These are transported in the blood by the same transport system wherever they are needed. "Glucose and vitamin C compete in this cellular-uptake process, like strangers trying to flag down the same taxicab simultaneously. Because glucose is greatly favoured in the contest, the uptake of vitamin C by cells is 'globally inhibited' when blood sugar levels are elevated. In effect, glucose regulates how much vitamin C is taken up by the cells, according to the University of Massachusetts nutritionist John Cunningham." (Gary Taubes).
The more glucose in the blood, the less vitamin C will be taken up by the cells, the more vitamin C will be lost in the urine. The key here, is not how much vitamin C we consume, but how much is absorbed by our body.
"It's not the absence of fruits and vegetables that causes scurvy; it's the presence of refined carbohydrates."
- Gary Taubes
So, the absence of a varied diet, might not be the cause of deficiencies, but rather the addition of refined carbohydrates and sugar may be the reason behind the appearance of vitamin and mineral deficiencies.