Carb Confusion!

Setting the record straight

I have seen several articles here on Medium discussing various topics related to nutrition. Often, the author gets around to discussing carbohydrate — one of the three macronutrients. It is here that a common point of misinformation/misunderstanding comes out. Many authors claim something along the lines of “the brain needs carbohydrate to operate,” or “the brain’s primary source of energy is carbohydrate.” Some will suggest that the primary source of energy for the entire body is carbohydrate, and therefore, it’s important that we eat our carbs!

Chances are that the misinformation comes from nutrition textbooks.

The Oxford Handbook of Nutrition and Dietetics, published in 2012, for example, suggests that 46.8% of daily calories for men and 47.8% of daily calories for women come from carbohydrate. They offer no reason why there is a 1 percentage point difference between the recommendation for men and women, nor do they offer any reasons for the overall recommendation of nearly 50% of calories coming from carbohydrate.

Understanding Nutrition by Eleanor Whitney and May Hamilton, initially published in 1977 says about the same thing. There are any number of theories as to why the misinformation exists in recent publications — that it is missing in older pubs is understandable. Also, I don’t blame the practitioners for not knowing the latest information in this area. But I do blame those who refuse to even look at the latest information and cast it aside because it doesn’t line up with what they learned in school.

The goal of this article is to set the record straight with respect to carbs — what they are, how they are metabolized and how much we need. Hopefully I’ll accomplish this goal in a fun-to-read way. I also hope that nutritionists, doctors and personal trainers will be willing to put their textbook knowledge aside and draw on their clinical/practical experience in evaluating the science-based information presented here (see references at the end of this article). To do so, I think doctors and nutritionists need to understand that the low-fat bias over the past 70 years is not based on any scientific information. In fact, it all started with a fraudulent paper published in a hospital newsletter (google “the seven-country study”).

The impact of this unscientific bias against eating fat is that our diet replaced fat with carbohydrate. The reason for this is that carbs are cheaper than protein and have a longer shelf-life — so food producers prefer to swap out fats with carbs. Besides, people tend to prefer foods that are high in carbohydrate.

The Carbohydrate Basics [1]

Carbohydrate is sugar. There are several simple sugars, including Glucose, Fructose and Galactose. With these simple sugars, each exists as a single molecule. There are also double sugars that contain a mix of 2 sugar molecules. For example, lactose is a combination of Glucose and Galactose, and Sucrose (table sugar) is a combination of Glucose and Fructose.

There are also Polysaccharides (“many” sugars). These come in two families — digestible and non-digestible. The digestible polysaccharides are called Glycogen if they are animal-based, and Starch if plant-based.

The non-digestible “many” sugars can be either water soluble or non-water soluble, but in either case, these are referred to as fiber. So, fiber is a form of sugar that is just not digestible.

Carbohydrate and Energy Production

Our cells need to produce energy to do the work they do. Most of our cells have mitochondria inside them that convert nutrients (glucose, fatty acids, amino acids and/or ketones) into the chemical energy needed for their work. But red blood cells don’t have mitochondria and can only use glucose to produce the energy they need. Without glucose, red blood cells would die — and we would follow quickly after.

As mentioned above, glucose is a simple sugar found in some foods containing carbohydrate. Glucose can either be found on its own or in a more complex sugar, such as sucrose. How much glucose we need is yet to be determined and will likely be forever unknown. For sure, we need some for our red blood cells. There is also speculation that parts of our brain need some amount of glucose. This might be true, but we will likely never know. Why? Because to find out, we’d need to remove glucose from the body — and that would lead to the death of our red blood cells, and then us.

But even if the brain needs some glucose, we do know that glucose isn’t the only source of nutrient energy available to the brain. The issue with the brain is something called the brain-blood barrier — it’s basically a filter that keeps toxins from reaching the brain. Glucose can pass this barrier — but amino acids and fatty acids cannot. This is what led people to believe that glucose was the only energy source for the brain. But we now know that the brain can — and does — use ketone bodies (derived from fatty acids in the liver) for fuel. Ketones can pass the blood-brain barrier. After a few days on a very low-carb diet, the brain will use ketones for about 25% of its energy needs [2]. After about four weeks of a low-carb diet, ketone bodies satisfy up to two-thirds of the brain’s energy demand. [3]

Do we need to eat carbohydrate?

The U.S. Department of Health and Human Services and U.S. Department of Agriculture 2015–2020: The Dietary Guidelines for Americans [4] defines an Essential Nutrient as “A vitamin, mineral, fatty acid, or amino acid required for normal body functioning that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health, and thus must be obtained from a dietary source.” In other words, “essential nutrients” are defined as nutrients we need to eat to allow our bodies to function normally. Note, they do not mention carbohydrate in their list of essential nutrients. This is not an error on their part. In 2005, the Panel on Macronutrients: Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) [5] concluded “The lower limit of dietary carbohydrate apparently is zero, provided that adequate amounts of protein and fat are consumed.” You can see, by the fact that they added the word “apparently” in their report, that they were surprised by this finding as well!

So, no, we don’t need to eat any carbohydrate to function normally.

How can this be if we need glucose and glucose comes from carbohydrate?

The answer is the process of gluconeogenesis. This process takes place in the liver. Through the process of gluconeogenesis, the liver takes fat — including body fat — and converts it into glucose! Recall, in the definition of an essential nutrient above, we don’t need to eat a nutrient if the body can synthesize enough of it for us to function normally. Well, the liver synthesizes glucose out of fat (and/or protein). We evolved with a failsafe process that synthesizes the nutrient our blood (and maybe parts of our brain) needs to stay alive. I think that’s pretty cool!

To close the loop:

Do we need to eat carbohydrate? No.

Do we need glucose? Yes.

How do we get the glucose we need if we don’t eat carbohydrate? Our body will synthesize all the glucose we need from the protein and fat we eat.

Thank you for reading this article — hopefully it contained something you found useful.

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References:

1. Biochemistry, 9th edition, Berg et al. 2019, W.H. Freeman and Company, NY, NY.
2. Hasselbalch, SG; Knudsen, GM; Jakobsen, J; Hageman, LP; Holm, S; Paulson, OB (1994). “Brain metabolism during short-term starvation in humans”. Journal of Cerebral Blood Flow and Metabolism. 14 (1): 125–31. doi:10.1038/jcbfm.1994.17. PMID 8263048.

3. Cahill GF. Fuel metabolism in starvation. Annu Rev Nutr 2006;26:1–22

4. The U.S. Department of Health and Human Services and U.S. Department of Agriculture 2015–2020: The Dietary Guidelines for Americans. 8th edition. (p91)

5. Panel on Macronutrients: Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients): The National Academies Press, 2005:1357

This article is intended for informational and educational purposes only. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment. You should not rely on this information as a substitute for, or a replacement of, professional medical advice, diagnosis or treatment. This article is not intended to prevent, diagnose or cure any medical condition, nor should it be construed as advice on medical nutrition. All viewers of this content should consult their physicians before beginning any nutrition, supplement or lifestyle program.