It’s frequently said in the Paleo blogosphere that carbs are unnecessary. Here’s an example from Don Matesz, an outstanding blogger who eats a diet extremely close to ours:
Protein is essential, carbs are not…. You can only cut protein so much, but you can cut carbs dramatically.
Dr. Michael Eades has mocked the idea of a carbohydrate deficiency disease:
Are there carbohydrate deficiency diseases, Mr. Harper, that you know about that the rest of the nutritional world doesn’t? I’ll clue you in: there aren’t. But there are both fat and protein deficiency diseases written about in every internal medicine textbook.
Such statements made an impression on me when I first started eating Paleo five years ago. But several years and health problems later, I realized that this view was mistaken.
Why Aren’t Carbohydrate Deficiency Diseases Known?
How do doctors discover the existence of a nutrient deficiency disease?
It’s not as easy as you might think. For example, the existence of essential fatty acid deficiency diseases in humans was in doubt right up into the 1950s, even though omega-6 deficiency disease had been discovered and characterized in rats in the 1920s. [1] The reason is that omega-6 and omega-3 deficiencies can occur only on unnatural diets. It was infants fed fat-free formula in the 1940s and 1950s who ended up proving the existence of omega-6 deficiency disease in humans.
Two difficulties have made it challenging for science to recognize a carbohydrate deficiency syndrome:
- Lack of an animal model.
- The rarity of zero-carb diets among humans.
Until recently, few people save the Inuit ate very low-carb diets, and the Inuit didn’t leave good medical records. As a result, few or no humans developed recorded carbohydrate deficiency syndromes.
This wouldn’t be a problem if it were possible to induce carbohydrate deficiency in animals. However, it isn’t.
Animals don’t get carbohydrate deficiency diseases because they have small brains, meaning low glucose needs, and big livers, meaning high glucose manufacturing capacity. Animals can generate all the glucose they need from protein or from volatile acids like propionate produced by bacterial fermentation in their digestive tracts.
But, as we note in the book, humans are more fragile. We have small livers and big brains, and so the possibility of glucose deficiency is real.
Here is a comparison of brain, liver, and gut sizes in humans and other primates [2]:
Organ | % body weight, humans | % body weight, other primates |
Brain | 2.0 | 0.7 |
Liver | 2.2 | 2.5 |
Gut | 1.7 | 2.9 |
The brain is the biggest determinant of glucose needs. While other primates need only about 7% of energy as glucose or ketones, humans need about 20%.
Compared to other primates, humans have a 12% smaller liver. This means we can’t manufacture as much glucose from protein as animals can. Humans also have a 40% smaller gut. This means we can’t manufacture many short-chain fatty acids, which supply ketones or glucogenic substrates, from plant fiber.
So, while animals can meet their tiny glucose needs (5% of calories) in their big livers, humans may not be able to meet our big glucose needs (20-30% of calories) from our small livers.
So any carbohydrate deficiency disease will strike humans only, not animals.
How Should We Look for a Carbohydrate Deficiency Disease?
To find a carbohydrate deficiency syndrome in humans, we should look at populations that eat very low-carb diets, such as:
- The Inuit on their traditional hunting diet.
- Epilepsy patients being treated with a ketogenic diet.
- Optimal Dieters in Poland, who have been following a very low-carb diet for more than 20 years.
- Very low-carb dieters in other countries, who took up low-carb dieting in the last 10 years as the Paleo movement gathered steam.
We should also have an idea what kind of symptoms we should be looking for. Major glucose-consuming parts of the body are:
- Brain and nerves.
- Immune system.
- Gut.
The body goes to great lengths to assure that the brain and nerves receive sufficient energy, so shortfalls in glucose are most likely to show up in immune and gut function.
So, we’ve mapped our project. Over the coming week, or however long it takes before we get tired, we’ll investigate the evidence for carbohydrate deficiency conditions in humans.
Related Posts
Other posts in this series:
- Dangers of Zero-Carb Diets, II: Mucus Deficiency and Gastrointestinal Cancers A Nov 15, 2010.
- Danger of Zero-Carb Diets III: Scurvy Nov 20, 2010.
- Dangers of Zero-Carb Diets, IV: Kidney Stones Nov 23, 2010.
References
[1] Holman RT. The slow discovery of the importance of omega 3 essential fatty acids in human health. J Nutr. 1998 Feb;128(2 Suppl):427S-433S. http://pmid.us/9478042
[2] Aiello LC, Wheeler P. The expensive tissue hypothesis: the brain and the digestive system in human and primate evolution. Current Anthropology 1995(Apr); 36(2):199-211.
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