The Carbohydrate Brain Fuel Myth

Dr. Eades continues. If "you’re following a low-carb diet...the protein you eat is converted to glucose....If you keep the carbs low enough so that the liver still has to make some sugar, then you will be in fat-burning mode....How low is low enough? Well, when the ketosis process is humming along nicely and the brain and other tissues have converted to ketones for fuel, the requirement for glucose drops to about 120-130 gm per day. If you keep your carbs below that at, say, 60 grams per day, you’re liver will have to produce at least 60-70 grams of glucose to make up the deficit, so you will generate ketones that entire time."

In fact, I give the ADA credit for citing the primary source in its "Nutrition Recommendations." That source is a report by the Institute of Medicine's food and nutrition board titled Dietary Reference Intakes: Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. The National Academies Press in 2002 published this book. While the ADA fails to provide a link,  fortunately for those of us who like to go to primary sources you can find it online.

What is this Institute of Medicine and why should we trust it? The Institute of Medicine and its parent organization, the National Academy of Sciences, are hybrid governmental-private organizations. The U.S. government created these private organizations to advise it on scientific and technological matters. Among their functions they set the official recommended dietary allowances for the macronutrients and micronutrients in our diet.

The Institute of Medicine takes 17 dense pages -- from page 277 to 293 -- to consider the evidence for estimating the average requirement for carbohydrate. I've studied them and encourage you to study the source for yourself. I don't need to copy or summarize its recommendations because Gary Taubes did it so well in his ground-breaking new book, Good Calories, Bad Calories, which I have written about here and in several other articles.

The IOM sets an "estimated average requirement" of 100 grams of carbohydrates a day for adults, Taubes writes, so that the brain can run exclusively on glucose, "without having to rely on a partial replacement of glucose by [ketone bodies]." It then sets the "recommended dietary allowance" at 130 grams to allow a margin for error. But the IOM report also acknowledges that the brain will be fine without these carbohydrates, because it runs perfectly well on ketone bodies, glycerol, and protein-derived glucose.

Many people don't understand what ketone bodies (or "ketones") are, confusing it with a dangerous condition called ketoacidosis. Dr. Eades, however, provides a clear explanation of why ketones are good.

"The liver requires energy to convert the protein to glucose," he writes on his blog. "The energy comes from fat. As the liver breaks down the fat to release its energy to power gluconeogenesis, the conversion of protein to sugar, it produces ketones as a byproduct. And what a byproduct they are. Ketones are basically water soluble (meaning they dissolve in blood) fats that are a source of energy for many tissues including the muscles, brain and heart. In fact, ketones act as a stand in for sugar in the brain. Although ketones can’t totally replace all the sugar required by the brain, they can replace a pretty good chunk of it."