And when I eat carbs such as fruit or whole grains I usually feel pretty spacey. If you are answering this and have tried or are on a low carb diet, do you find that without glucose you think slower?
“Ketones have been described as “magic” in their ability to increase metabolic efficiency, while decreasing production of free radicals, the damaging byproducts of normal metabolism. The heart and brain operate 25% more efficiently using ketones as a source of energy.”
I have no doubt that the first week or two with the fuel changeover that some people have problems, but when the body becomes fat adapted (it can take 3-6 weeks to become fat adapted sufficiently for athletic performance) the body is working most efficiently.
This is my problem with carb cycling programs, they never allow the body to become fully fat adapted, which I believe takes 6 weeks. I fear the metabolism will just shut down & await a return to glycolysis.
The body wants to be in glycolysis, it’s so much easier. The body uses alcohol even more efficiently than carbs to fuel the body, but there has never been dispute about the effects of alcohol in the destruction of the human body. Easy & efficient does not equate to healthy, the body has to have many defenses to counteract the damaging effects of glycolysis. Glycolysis creates production of free radicals which oxidizes the body (somewhat akin to rust oxidizing metal). The body also creates VLDL only during carbohydrate metabolism. My theory is to bandage the damage done by glycation which creates thick arterial walls reducing blood flow.
I think that ketosis is not the back up fuel plan. I think ketosis was meant to be primary fuel plan, that is easily overridden (one bite) by ingestion of carbs (or alcohol). The body is rarely allowed to become fully fat adapted, especially in these days of people using processed food formula to feed infants instead of breast milk. Carbs were never supposed to be available year around, only seasonally during harvest. The body can easily handle carbs even in excess occasionally, just not continuously. The body can also be fueled by protein (via gluconeogenesis) but long term protein synthesis creates the byproducts of ammonia & nitrogen. The body can easily handle clearing out these byproducts but if gluconeogenesis is used as the primary fuel source for long term, the body can be overwhelmed (poisoned) by the excess ammonia & nitrogen. It’s all contingent on balance but the body functions at optimal levels on more dietary fat & suboptimal levels on less dietary fat. The body is a self healing unit & has many defenses to rid the body of toxins. If you input more toxins faster than the body can clear them out, you create a breakdown in the entire system.
The body always has the ability to use ketone bodies as fuel. Even people in glycolysis (except those that are hyperinsulimic) burn some fat as they sleep, this helps preserve glycogen stores. Using fat as fuel & being fueled by fat are the difference in the body becoming fully fat adaped to being fueled by ketone bodies & glycerol.
It’s not an instantaneous process, athletes reach this stage when they “hit the wall” by depleting glycogen stores, but they still only just do a fuel changeover. It still takes time for the body to become fully fat adapted to being fueled by fat stores.
This study referenced:
show that the body (even for athletes) become fat adapted *with time* & allow unimpaired endurance performance despite nutritional ketosis.
“The most obvious of these is the time allotted (or not) for keto-adaptation. In this context, the prescient observation of Schwatka (that adaptation to “a diet of reindeer meat” takes 2–3 weeks) says it all. None of the comparative low-carbohydrate versus high-carbohydrate studies done in support of the carbohydrate loading hypothesis sustained the low carbohydrate diet for more than 2 weeks ….
There are to date no studies that carefully examine the optimum length of this keto-adaptation period, but it is clearly longer than one week and likely well advanced within 3–4 weeks. The process does not appear to happen any faster in highly trained athletes than in overweight or untrained individuals. This adaptation process also appears to require consistent adherence to carbohydrate restriction, as people who intermittently consume carbohydrates while attempting a ketogenic diet report subjectively reduced exercise tolerance.”
This also seems to suggest that after one has become fat adapted, endurance exercise performance returns to normal, but sprint performance remains poor. The suggested reason is that this type of exercise can not be fueled by fat, it must be fueled by glucose.
Glucose is the bodies preferred fuel (if you want to get technical, it actually burns alcohol most efficiently), the body can convert 100% of carbs, 58% of protein & 10% of dietary fat into glucose. The body can also be fueled by fat (dietary fat & fat cells) but only in the absence of carbs. Your brain actually prefers* to be fueled by ketones (part of the fat burning process), it does require glucose also, but glucose can be easily converted from excess protein if needed or dietary fat.
After 3 days of carb restriction, the liver synthesizes ketone bodies from precursors obtained from fatty acid breakdown. The brain uses these ketone bodies as fuel, thus cutting its need for glucose. After 3 days, the brain gets 30% of its energy from ketone bodies. After 4 days, this goes up to 70%. Thus, the production of ketone bodies & glycerol cuts the brain’s glucose requirement from 120 g per day to about 10 g per day.