Myth 1: The human brain burns 600 kcal per day glucose to meet its energy needs.
Myth 2: No one can follow a ketogenic diet long term.
The need for dietary carbohydrates is often a topic of misunderstanding and misinformation. Although some specific tissues in the body do have certain glucose requirements, these requirements are easily met by gluconeogenic sources within the body without the need for dietary carbohydrate intake. The fatigue, stress, impaired cognition and reduced performance that are often used to argue for the need for carbohydrate are more aptly attributable to improper implementation of a well-formulated ketogenic diet (WFKD), inadequate electrolyte replacement, and/or insufficient time for keto-adaptation. When used correctly, a ketogenic diet can be a safe and sustainable therapeutic tool as well as a means to help promote wellness and performance.
The specific topic that we want to address here is how both the brain and body can function as well – or even better – on a diet with little or no dietary carbohydrate compared to the typically promoted low fat, high carbohydrate ‘healthy diet.’
Published science has shown that ketones that are produced from either dietary fats or triglycerides stored in our adipose (fat) tissue reserves are an excellent fuel for the brain. Further, we now know that these ketones produced by the liver also have multiple beneficial effects on the heart, kidneys, and other organs that appear to translate into improved longevity.
Additionally, new research has highlighted that skeletal muscles, even those of competitive athletes, are not solely dependent on high dietary carbohydrate intake for glycogen replenishment and performance.
Ketones are a cleaner-burning fuel (i.e., producing fewer free-radicals) than glucose when used by the brain and other organs. The primary ketone beta-hydroxybutyrate (BOHB) can also function as a signal to activate genes that regulate our defenses against oxidative stress and inflammation.
The shifting they body’s energy source from carbohydrates to fats, which we have named ‘keto-adaptation,’ starts within days but takes a considerable period of time to fully develop. The result is maintenance of normal blood glucose and muscle glycogen levels that can be sustained without the need for dietary carbohydrate intake.
Physiologic Role of Carbohydrates
The presumed requirement for glucose by the brain is a conditional need that is based on the fuel sources dictated by one’s choice of diet. A ketone-suppressing diet (i.e., any diet supplying >30% of energy from the combined intakes of carbohydrate and protein) essentially forces the brain to rely on glucose for fuel.
It is true that some cells within the body do require glucose. But in all of these cases where glucose is broken down to lactate, the body can recycle that lactate back to glucose.
Evidence That the Brain Can Function on Ketones
The simplest experiment that demonstrates the brain’s ability to function on ketones is the observation that humans can tolerate total fasting with normal mental function for durations of 30-60 days. Elegantly done studies that measured glucose and ketone levels in arterial blood going into the brain compared to these fuels in the jugular vein coming out of the brain, indicated that ketones are in fact able to supply the great majority of the brain’s energy.
See the original Virta post for the studies.
What these studies demonstrated is clear evidence of normal brain function in the virtual absence of glucose when sufficient ketones are available. This offers us the unique perspective that when consuming a carbohydrate-rich diet the predominate source of fuel for the brain is glucose; not because it is needed but because the other natural and highly effective brain energy source has been shut off.Butunder conditions of consistent nutritional ketosis, the brain adapts to the presence of ketones by enhancing their uptake and oxidation, thus protecting cognitive and CNS (central nervous system) function.
Essentials of Keto-Adaptation – Glucose Conservation and Salvage
Just because one doesn’t consume dietary carbohydrate does not mean the body is completely lacking in glucose. Whether fasting or on a meat-and-fat-only ketogenic diet, blood glucose values remain in the normal range both at rest and during exercise. This occurs because the body is quite capable of synthesizing all of the glucose it needs from various gluconeogenic precursors, while at the same time strictly limiting its rate of carbohydrate oxidation.
There are at least five sources of these glucose precursors:
- breakdown of muscle to supply amino acids for gluconeogenesis;
- breakdown of dietary protein to supply amino acids for gluconeogenesis,
- glycerol released from the hydrolysis of adipose tissue triglyceride or dietary triglyceride;
- recycling lactate and pyruvate from glycolysis; and
- acetone produced by the spontaneous breakdown of acetoacetate to acetone that can be used for gluconeogenesis.
The conditions for and the amounts provided by these various sources of gluconeogenesis are shown in the following table.
What this table clearly demonstrates is that whether during a total fast or a ketogenic diet without carbohydrate containing foods, new or recycled gluconeogenic substrates provide for the generation of anywhere from 100-200 g/d of glucose. Add to this up to 50 g/d of dietary carbohydrate as part of a WFKD, and it becomes clear why nutritional ketosis is well tolerated under a variety of challenging conditions.
Lessons from Low Carbohydrate Athletes
Dr. Volek’s group recruited 20 competitive ultra-runners, 10 of whom followed a traditional high carbohydrate diet and the other 10 had been following a ketogenic diet for at least 6 months.
After baseline testing, these runners were asked to do a 3-hour run at race-pace on a treadmill. Surprisingly, both groups had similar muscle glycogen levels before the run, and they also both mobilized similar amounts (about 80%) of their glycogen during 3 hours on the treadmill.
But almost 90% of ketogenic runner’s net energy use was from fat. This is an astonishing example of being able to maintain normal muscle glycogen while consuming very little carbohydrate.
Please refer to the original Virta post for 2 more in depth studies.
Why Some Experts Still Claim that We Need Dietary Carbohydrates
There are some other arguments used to support the idea that we need to consume carbohydrates above levels that facilitate nutritional ketosis.
Thyroid dysfunction:The blood level of the active thyroid hormone T3 typically falls by 30-40% in the first few weeks of a WFKD, but this is not accompanied by any signs or symptoms of clinical hypothyroidism. This change is due to a marked reduction in thyroid hormone resistance during nutritional ketosis, which can be eased with adequate electrolytes intake. Therefore, this is a healthy response and not a sign of endocrine dysfunction.
Sleep patterns are disturbed by a ketogenic diet. In our study we found that global sleep quality, sleep disturbances, and daytime dysfunction parameters all were significantly improved. In addition, the proportion of patients reporting poor sleep was significantly reduced after 1 year.
We need more dietary fiber than is possible on a ketogenic diet.What we point out in our blog post on fiber is that the production of BOHB can provide many-fold more SCFAs to the brain than a very high fiber diet combined with an optimized microbiome. Thus, the moderate level of fiber that one can achieve with a real-food WFKD should be more than adequate to maintain health.
To learn more, please see my Blog Post, Fiber and Colon Health On A Well-Formulated Ketogenic Diet https://2healthyhabits.wordpress.com/2019/03/08/fiber-and-colon-health-on-a-well-formulated-ketogenic-diet-new-insights-question-its-role-as-an-unconditional-requirement/
This Post has been condensed from the original Virta Post: Why Humans Don’t Need Dietary Carbohydrates to Thrive By Stephen Phinney, MD, PhD, Brooke Bailey, Ph.D Jeff Volek, PhD, RD https://blog.virtahealth.com/why-dont-need-dietary-carbohydrates/?fbclid=IwAR0gDnfRCWEimOQgsK8sCEY7-Rh5R6E5TyyISAOd3VbSj71OsKOEekmTTO0
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