Overview
Glucose is the cleanest fuel the body has and is the one our brain, red blood cells and most tissues prefer. Burning glucose in the mitochondria produces carbon dioxide, ATP, and heat, without the destructive byproducts that fat oxidation generates. When glucose oxidation is working, lactic acid stays low, the stress hormones are kept in check and cells maintain the energy reserve they need to do their work. When low thyroid, elevated free fatty acids, polyunsaturated fats, or genuine starvation impairs glucose oxidation, the body shifts into a primitive glycolytic metabolism. This produces lactic acid, drives inflammation, and accelerates aging and cancer. The popular idea that sugar feeds disease has the relationship backwards: it is the inability to use glucose properly, not glucose itself, that is destructive.
Key Points
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Glucose oxidation is the central energy process and it produces carbon dioxide as a stabilizing byproduct. When a cell burns glucose all the way through, it generates many times more ATP than glycolysis alone, and the carbon dioxide that streams out of the cell turns off lactic acid production, quiets excitation, and binds calcium so it can be carried to the bones rather than be deposited in soft tissues. Oxidizing fat does not produce nearly as much carbon dioxide, which is one reason a fat-burning metabolism tilts cells toward the inflammatory glycolytic state.
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Free fatty acids in the blood block the cell's ability to use glucose. This is the Randle effect, established in the 1960s. The moment fatty acids rise, pyruvate dehydrogenase, the enzyme that lets cells oxidize glucose, gets shut off. The result is functional diabetes regardless of insulin status, because glucose can no longer enter the oxidative pathway. Stress, fasting, polyunsaturated fats, and excess cortisol all liberate fatty acids and produce this blockade.
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Liver glycogen should hold roughly eight hours of glucose, and failure to store it activates the stress system. A healthy liver with adequate thyroid stores enough glycogen to get through the night without resorting to adrenaline or cortisol. When glycogen runs out, adrenaline rises first to squeeze out the last of the liver's reserves, producing shakiness, cold extremities, and waking. If adrenaline cannot mobilize enough, ACTH and cortisol take over and start dissolving the thymus, muscles, and other tissues to convert protein into glucose.
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Sugar lowers cortisol, and many "diabetics" actually have a cortisol problem. Cortisol drives blood sugar up by breaking down tissue, which can mimic diabetes on a glucose test. Ray observed that patients labeled diabetic often had high cortisol and that giving them sugar lowered the cortisol and produced a quick recovery.
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Glucose stimulates regeneration of pancreatic beta cells from stem cells. The pancreas is constantly attempting to renew its insulin-producing beta cells from stem cells via the alpha cells, and glucose is the signal that supports this regeneration. Polyunsaturated fats and the prostaglandins they form are toxic to newly formed beta cells, so without enough glucose to suppress fatty acid release, every newly born beta cell gets killed. The diabetes epidemic matches the rise in polyunsaturated fat consumption, not sugar consumption.
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The brain runs on glucose and cannot maintain itself without it. Without glycogen the brain fails the same way it does in sleep deprivation which leads to confusion, inability to think and eventually death. Sleep is the process by which glycogen gets restored so the brain can function on a pure glucose regime again. Removing carbohydrate forces the body to break down muscle, connective tissue, and glandular tissue to manufacture glucose, which keeps a person alive but degrades every functional system.
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A blood glucose spike followed by a clean drop is the sign of a healthy person. When a healthy person eats white rice, glucose rises, insulin rises, then both drop back to baseline. That is normal physiology. A diabetic is someone whose blood glucose spikes and stays up because their cells cannot oxidize the sugar. Chasing a flat blood sugar curve with allulose, acarbose, or pharmaceutical glucose-blunting drugs is treating the wrong target. Some health influencers brag about never letting blood sugar exceed 115, with no study showing that pursuing this produces any benefit.
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Sugar does not cause cancer; the inability to oxidize glucose properly is what cancer cells exhibit. Otto Warburg showed that cancer cells convert glucose to lactic acid even in the presence of oxygen because their mitochondria are impaired. He never said glucose causes cancer. Withholding sugar from a cancer patient accelerates wasting, because the body raises cortisol and breaks down healthy tissues faster to feed the tumor, which can run on amino acids and fats just as well. Intravenous glucose plus oxygen has been shown to revert the Ehrlich ascites carcinoma to normal metabolism.
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Pure glucose and fast-digesting starch produce stronger insulin spikes than fruit, milk, or white sugar. Starch hits the bloodstream as pure glucose almost as quickly as a glucose tablet would, near the top of the glycemic index. That triggers a strong insulin response, which converts exess glucose into fat rather than glycogen and forces a rebound cortisol surge. The fructose in sucrose, fruit, and honey moderates the insulin response, slows absorption slightly, and directs more of the glucose to liver glycogen storage rather than adipose tissue.
Notable Quotes
"The diabetic can't produce any energy from glucose. So they have to tear down their protein and even that doesn't work. So they die by wasting away"
[Ray Peat — All Things Hormones, Metabolism and Health]
"Sugar deprivation turns on the Warburg effect."
[Ray Peat — The Metabolism of Cancer]
"The obvious way to stop the stress reaction is to provide enough glucose and oxygen along with the other nutrients."
[Ray Peat — Cortisol and Low Testosterone]
"If you arrive in a really critical condition in the hospital, one of the first things they do is hook you up to a glucose drip. They don't give you a fat drip. They don't give you a protein drip. They give you a glucose drip and they keep you on that glucose drip until you stabilize."
[Georgi Dinkov — Why You May Need More Carbs in Your Diet, Interview with Dr. Mercola]
Important Things To Consider
Pure glucose and starch alone, without other minerals, drive fat synthesis. A large dose of pure glucose or fast-cooked starch hits the liver faster than it can be stored as glycogen, so the excess gets converted to fat. Without potassium, magnesium, and other minerals from fruit or milk, the insulin response is stronger and more disruptive. This is one reason fruit and milk handle the same gram count of sugar more smoothly than bread or candy.
Low thyroid is the most common reason a liver cannot store glycogen. Without active thyroid hormone, the enzymes that build glycogen from glucose work poorly, regardless of how much sugar is eaten. Selenium deficiency compounds the problem because selenium is needed to activate thyroid. Eating sugar without addressing the underlying thyroid state produces only a transient effect and the person stays trapped in the high-stress-hormone pattern.
Bacterial overgrowth in the upper intestine can make sugar feel intolerable. People who have been low thyroid for a long time develop bacteria or even fungal growth high up in the small intestine. The bacteria intercept sugar before it can be absorbed, producing crashes, dizziness and, in rare cases, actual alcohol fermentation in the stomach. This presents as "sugar intolerance" but the real problem is the bacterial overgrowth driven by the underlying low thyroid state.
Eating only protein produces the same cortisol surge as fasting. A pure protein meal causes a sharp drop in blood sugar a few hours later, which triggers cortisol and starts the same wasting cascade as not eating at all. Protein needs to be eaten with sugar so the cortisol does not rise to convert the amino acids to glucose. Roughly 100 grams of carbohydrate per day is a minimum, and 200 to 300 grams may be appropriate for someone physically active.
De novo lipogenesis from sugar requires very high intake to be relevant. You need to eat upwards of a pound of sugar a day before the body's fat synthesis machinery kicks in meaningfully. Most people are nowhere near that. The "sugar makes you fat" claim is technically true at extreme intakes that almost nobody actually consumes.
The cell becomes alkaline when stressed, not acidic, even though it dumps acid into its surroundings. A healthy respiring cell sits around pH 6.8 because of the carbon dioxide it is constantly producing. Under stress the cell stops making carbon dioxide and starts making lactic acid, which it pumps out, raising the cell's internal pH and acidifying the surrounding tissue. The popular advice to "alkalize" the body misreads this entirely. The internal alkalinity is the disease state, and the carbon dioxide produced by burning glucose is what protects against it.
If glucose is poorly metabolized, the fix is reducing fat supply, not eliminating glucose. Niacinamide, aspirin, or vitamin E all suppress excessive lipolysis and restore the cell's ability to oxidize glucose. A single 300 mg dose of niacinamide dropped triglycerides by 75 percent in one study without any change to diet. Treating the fat side of the Randle cycle is more effective than restricting carbs.
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